systemd.exec - Execution environment configuration - man(5) - [phpMan]

Che Dong

SYSTEMD.EXEC(5) systemd.exec SYSTEMD.EXEC(5)

NAME
systemd.exec - Execution environment configuration

SYNOPSIS
service.service, socket.socket, mount.mount, swap.swap

DESCRIPTION
Unit configuration files for services, sockets, mount points, and swap devices share a subset
of configuration options which define the execution environment of spawned processes.

This man page lists the configuration options shared by these four unit types. See
systemd.unit(5) for the common options of all unit configuration files, and
systemd.service(5), systemd.socket(5), systemd.swap(5), and systemd.mount(5) for more
information on the specific unit configuration files. The execution specific configuration
options are configured in the [Service], [Socket], [Mount], or [Swap] sections, depending on
the unit type.

In addition, options which control resources through Linux Control Groups (cgroups) are
listed in systemd.resource-control(5). Those options complement options listed here.

IMPLICIT DEPENDENCIES
A few execution parameters result in additional, automatic dependencies to be added:

• Units with WorkingDirectory=, RootDirectory=, RootImage=, RuntimeDirectory=,
StateDirectory=, CacheDirectory=, LogsDirectory= or ConfigurationDirectory= set
automatically gain dependencies of type Requires= and After= on all mount units required
to access the specified paths. This is equivalent to having them listed explicitly in
RequiresMountsFor=.

• Similarly, units with PrivateTmp= enabled automatically get mount unit dependencies for
all mounts required to access /tmp/ and /var/tmp/. They will also gain an automatic
After= dependency on systemd-tmpfiles-setup.service(8).

• Units whose standard output or error output is connected to journal or kmsg (or their
combinations with console output, see below) automatically acquire dependencies of type
After= on systemd-journald.socket.

• Units using LogNamespace= will automatically gain ordering and requirement dependencies
on the two socket units associated with systemd-journald@.service instances.

PATHS
The following settings may be used to change a service's view of the filesystem. Please note
that the paths must be absolute and must not contain a ".." path component.

ExecSearchPath=
Takes a colon separated list of absolute paths relative to which the executable used by
the Exec*= (e.g. ExecStart=, ExecStop=, etc.) properties can be found. ExecSearchPath=
overrides $PATH if $PATH is not supplied by the user through Environment=,
EnvironmentFile= or PassEnvironment=. Assigning an empty string removes previous
assignments and setting ExecSearchPath= to a value multiple times will append to the
previous setting.

Added in version 250.

WorkingDirectory=
Takes a directory path relative to the service's root directory specified by
RootDirectory=, or the special value "~". Sets the working directory for executed
processes. If set to "~", the home directory of the user specified in User= is used. If
not set, defaults to the root directory when systemd is running as a system instance and
the respective user's home directory if run as user. If the setting is prefixed with the
"-" character, a missing working directory is not considered fatal. If
RootDirectory=/RootImage= is not set, then WorkingDirectory= is relative to the root of
the system running the service manager. Note that setting this parameter might result in
additional dependencies to be added to the unit (see above).

RootDirectory=
Takes a directory path relative to the host's root directory (i.e. the root of the system
running the service manager). Sets the root directory for executed processes, with the
chroot(2) system call. If this is used, it must be ensured that the process binary and
all its auxiliary files are available in the chroot() jail. Note that setting this
parameter might result in additional dependencies to be added to the unit (see above).

The MountAPIVFS= and PrivateUsers= settings are particularly useful in conjunction with
RootDirectory=. For details, see below.

If RootDirectory=/RootImage= are used together with NotifyAccess= the notification socket
is automatically mounted from the host into the root environment, to ensure the
notification interface can work correctly.

Note that services using RootDirectory=/RootImage= will not be able to log via the syslog
or journal protocols to the host logging infrastructure, unless the relevant sockets are
mounted from the host, specifically:

The host's os-release(5) file will be made available for the service (read-only) as
/run/host/os-release. It will be updated automatically on soft reboot (see: systemd-soft-
reboot.service(8)), in case the service is configured to survive it.

Example 1. Mounting logging sockets into root environment

BindReadOnlyPaths=/dev/log /run/systemd/journal/socket /run/systemd/journal/stdout

This option is only available for system services, or for services running in per-user
instances of the service manager in which case PrivateUsers= is implicitly enabled
(requires unprivileged user namespaces support to be enabled in the kernel via the
"kernel.unprivileged_userns_clone=" sysctl).

RootImage=
Takes a path to a block device node or regular file as argument. This call is similar to
RootDirectory= however mounts a file system hierarchy from a block device node or
loopback file instead of a directory. The device node or file system image file needs to
contain a file system without a partition table, or a file system within an MBR/MS-DOS or
GPT partition table with only a single Linux-compatible partition, or a set of file
systems within a GPT partition table that follows the Discoverable Partitions
Specification[1].

When DevicePolicy= is set to "closed" or "strict", or set to "auto" and DeviceAllow= is
set, then this setting adds /dev/loop-control with rw mode, "block-loop" and
"block-blkext" with rwm mode to DeviceAllow=. See systemd.resource-control(5) for the
details about DevicePolicy= or DeviceAllow=. Also, see PrivateDevices= below, as it may
change the setting of DevicePolicy=.

Units making use of RootImage= automatically gain an After= dependency on
systemd-udevd.service.

This option is only available for system services and is not supported for services
running in per-user instances of the service manager.

Added in version 233.

RootImageOptions=
Takes a comma-separated list of mount options that will be used on disk images specified
by RootImage=. Optionally a partition name can be prefixed, followed by colon, in case
the image has multiple partitions, otherwise partition name "root" is implied. Options
for multiple partitions can be specified in a single line with space separators.
Assigning an empty string removes previous assignments. Duplicated options are ignored.
For a list of valid mount options, please refer to mount(8).

Valid partition names follow the Discoverable Partitions Specification[1]: root, usr,
home, srv, esp, xbootldr, tmp, var.

This option is only available for system services and is not supported for services
running in per-user instances of the service manager.

Added in version 247.

RootEphemeral=
Takes a boolean argument. If enabled, executed processes will run in an ephemeral copy of
the root directory or root image. The ephemeral copy is placed in
/var/lib/systemd/ephemeral-trees/ while the service is active and is cleaned up when the
service is stopped or restarted. If RootDirectory= is used and the root directory is a
subvolume, the ephemeral copy will be created by making a snapshot of the subvolume.

To make sure making ephemeral copies can be made efficiently, the root directory or root
image should be located on the same filesystem as /var/lib/systemd/ephemeral-trees/. When
using RootEphemeral= with root directories, btrfs(5) should be used as the filesystem and
the root directory should ideally be a subvolume which systemd can snapshot to make the
ephemeral copy. For root images, a filesystem with support for reflinks should be used to
ensure an efficient ephemeral copy.

This option is only available for system services and is not supported for services
running in per-user instances of the service manager.

Added in version 254.

RootHash=
Takes a data integrity (dm-verity) root hash specified in hexadecimal, or the path to a
file containing a root hash in ASCII hexadecimal format. This option enables data
integrity checks using dm-verity, if the used image contains the appropriate integrity
data (see above) or if RootVerity= is used. The specified hash must match the root hash
of integrity data, and is usually at least 256 bits (and hence 64 formatted hexadecimal
characters) long (in case of SHA256 for example). If this option is not specified, but
the image file carries the "user.verity.roothash" extended file attribute (see xattr(7)),
then the root hash is read from it, also as formatted hexadecimal characters. If the
extended file attribute is not found (or is not supported by the underlying file system),
but a file with the .roothash suffix is found next to the image file, bearing otherwise
the same name (except if the image has the .raw suffix, in which case the root hash file
must not have it in its name), the root hash is read from it and automatically used, also
as formatted hexadecimal characters.

If the disk image contains a separate /usr/ partition it may also be Verity protected, in
which case the root hash may configured via an extended attribute "user.verity.usrhash"
or a .usrhash file adjacent to the disk image. There's currently no option to configure
the root hash for the /usr/ file system via the unit file directly.

This option is only available for system services and is not supported for services
running in per-user instances of the service manager.

Added in version 246.

RootHashSignature=
Takes a PKCS7 signature of the RootHash= option as a path to a DER-encoded signature
file, or as an ASCII base64 string encoding of a DER-encoded signature prefixed by
"base64:". The dm-verity volume will only be opened if the signature of the root hash is
valid and signed by a public key present in the kernel keyring. If this option is not
specified, but a file with the .roothash.p7s suffix is found next to the image file,
bearing otherwise the same name (except if the image has the .raw suffix, in which case
the signature file must not have it in its name), the signature is read from it and
automatically used.

If the disk image contains a separate /usr/ partition it may also be Verity protected, in
which case the signature for the root hash may configured via a .usrhash.p7s file
adjacent to the disk image. There's currently no option to configure the root hash
signature for the /usr/ via the unit file directly.

This option is only available for system services and is not supported for services
running in per-user instances of the service manager.

Added in version 246.

RootVerity=
Takes the path to a data integrity (dm-verity) file. This option enables data integrity
checks using dm-verity, if RootImage= is used and a root-hash is passed and if the used
image itself does not contain the integrity data. The integrity data must be matched by
the root hash. If this option is not specified, but a file with the .verity suffix is
found next to the image file, bearing otherwise the same name (except if the image has
the .raw suffix, in which case the verity data file must not have it in its name), the
verity data is read from it and automatically used.

This option is supported only for disk images that contain a single file system, without
an enveloping partition table. Images that contain a GPT partition table should instead
include both root file system and matching Verity data in the same image, implementing
the Discoverable Partitions Specification[1].

This option is only available for system services and is not supported for services
running in per-user instances of the service manager.

Added in version 246.

RootImagePolicy=, MountImagePolicy=, ExtensionImagePolicy=
Takes an image policy string as per systemd.image-policy(7) to use when mounting the disk
images (DDI) specified in RootImage=, MountImage=, ExtensionImage=, respectively. If not
specified the following policy string is the default for RootImagePolicy= and
MountImagePolicy:

root=verity+signed+encrypted+unprotected+absent: \
usr=verity+signed+encrypted+unprotected+absent: \
home=encrypted+unprotected+absent: \
srv=encrypted+unprotected+absent: \
tmp=encrypted+unprotected+absent: \
var=encrypted+unprotected+absent

The default policy for ExtensionImagePolicy= is:

root=verity+signed+encrypted+unprotected+absent: \
usr=verity+signed+encrypted+unprotected+absent

Added in version 254.

MountAPIVFS=
Takes a boolean argument. If on, a private mount namespace for the unit's processes is
created and the API file systems /proc/, /sys/, /dev/ and /run/ (as an empty "tmpfs") are
mounted inside of it, unless they are already mounted. Note that this option has no
effect unless used in conjunction with RootDirectory=/RootImage= as these four mounts are
generally mounted in the host anyway, and unless the root directory is changed, the
private mount namespace will be a 1:1 copy of the host's, and include these four mounts.
Note that the /dev/ file system of the host is bind mounted if this option is used
without PrivateDevices=. To run the service with a private, minimal version of /dev/,
combine this option with PrivateDevices=.

In order to allow propagating mounts at runtime in a safe manner, /run/systemd/propagate/
on the host will be used to set up new mounts, and /run/host/incoming/ in the private
namespace will be used as an intermediate step to store them before being moved to the
final mount point.

Added in version 233.

ProtectProc=
Takes one of "noaccess", "invisible", "ptraceable" or "default" (which it defaults to).
When set, this controls the "hidepid=" mount option of the "procfs" instance for the unit
that controls which directories with process metainformation (/proc/PID) are visible and
accessible: when set to "noaccess" the ability to access most of other users' process
metadata in /proc/ is taken away for processes of the service. When set to "invisible"
processes owned by other users are hidden from /proc/. If "ptraceable" all processes that
cannot be ptrace()'ed by a process are hidden to it. If "default" no restrictions on
/proc/ access or visibility are made. For further details see The /proc Filesystem[2]. It
is generally recommended to run most system services with this option set to "invisible".
This option is implemented via file system namespacing, and thus cannot be used with
services that shall be able to install mount points in the host file system hierarchy.
Note that the root user is unaffected by this option, so to be effective it has to be
used together with User= or DynamicUser=yes, and also without the "CAP_SYS_PTRACE"
capability, which also allows a process to bypass this feature. It cannot be used for
services that need to access metainformation about other users' processes. This option
implies MountAPIVFS=.

If the kernel doesn't support per-mount point hidepid= mount options this setting remains
without effect, and the unit's processes will be able to access and see other process as
if the option was not used.

This option is only available for system services and is not supported for services
running in per-user instances of the service manager.

Added in version 247.

ProcSubset=
Takes one of "all" (the default) and "pid". If "pid", all files and directories not
directly associated with process management and introspection are made invisible in the
/proc/ file system configured for the unit's processes. This controls the "subset=" mount
option of the "procfs" instance for the unit. For further details see The /proc
Filesystem[2]. Note that Linux exposes various kernel APIs via /proc/, which are made
unavailable with this setting. Since these APIs are used frequently this option is useful
only in a few, specific cases, and is not suitable for most non-trivial programs.

Much like ProtectProc= above, this is implemented via file system mount namespacing, and
hence the same restrictions apply: it is only available to system services, it disables
mount propagation to the host mount table, and it implies MountAPIVFS=. Also, like
ProtectProc= this setting is gracefully disabled if the used kernel does not support the
"subset=" mount option of "procfs".

Added in version 247.

BindPaths=, BindReadOnlyPaths=
Configures unit-specific bind mounts. A bind mount makes a particular file or directory
available at an additional place in the unit's view of the file system. Any bind mounts
created with this option are specific to the unit, and are not visible in the host's
mount table. This option expects a whitespace separated list of bind mount definitions.
Each definition consists of a colon-separated triple of source path, destination path and
option string, where the latter two are optional. If only a source path is specified the
source and destination is taken to be the same. The option string may be either "rbind"
or "norbind" for configuring a recursive or non-recursive bind mount. If the destination
path is omitted, the option string must be omitted too. Each bind mount definition may be
prefixed with "-", in which case it will be ignored when its source path does not exist.

BindPaths= creates regular writable bind mounts (unless the source file system mount is
already marked read-only), while BindReadOnlyPaths= creates read-only bind mounts. These
settings may be used more than once, each usage appends to the unit's list of bind
mounts. If the empty string is assigned to either of these two options the entire list of
bind mounts defined prior to this is reset. Note that in this case both read-only and
regular bind mounts are reset, regardless which of the two settings is used.

This option is particularly useful when RootDirectory=/RootImage= is used. In this case
the source path refers to a path on the host file system, while the destination path
refers to a path below the root directory of the unit.

Note that the destination directory must exist or systemd must be able to create it.
Thus, it is not possible to use those options for mount points nested underneath paths
specified in InaccessiblePaths=, or under /home/ and other protected directories if
ProtectHome=yes is specified. TemporaryFileSystem= with ":ro" or ProtectHome=tmpfs
should be used instead.

Added in version 233.

MountImages=
This setting is similar to RootImage= in that it mounts a file system hierarchy from a
block device node or loopback file, but the destination directory can be specified as
well as mount options. This option expects a whitespace separated list of mount
definitions. Each definition consists of a colon-separated tuple of source path and
destination definitions, optionally followed by another colon and a list of mount
options.

Mount options may be defined as a single comma-separated list of options, in which case
they will be implicitly applied to the root partition on the image, or a series of
colon-separated tuples of partition name and mount options. Valid partition names and
mount options are the same as for RootImageOptions= setting described above.

Each mount definition may be prefixed with "-", in which case it will be ignored when its
source path does not exist. The source argument is a path to a block device node or
regular file. If source or destination contain a ":", it needs to be escaped as "\:". The
device node or file system image file needs to follow the same rules as specified for
RootImage=. Any mounts created with this option are specific to the unit, and are not
visible in the host's mount table.

These settings may be used more than once, each usage appends to the unit's list of mount
paths. If the empty string is assigned, the entire list of mount paths defined prior to
this is reset.

This option is only available for system services and is not supported for services
running in per-user instances of the service manager.

Added in version 247.

ExtensionImages=
This setting is similar to MountImages= in that it mounts a file system hierarchy from a
block device node or loopback file, but instead of providing a destination path, an
overlay will be set up. This option expects a whitespace separated list of mount
definitions. Each definition consists of a source path, optionally followed by a colon
and a list of mount options.

A read-only OverlayFS will be set up on top of /usr/ and /opt/ hierarchies for sysext
images and /etc/ hierarchy for confext images. The order in which the images are listed
will determine the order in which the overlay is laid down: images specified first to
last will result in overlayfs layers bottom to top.

Each mount definition may be prefixed with "-", in which case it will be ignored when its
source path does not exist. The source argument is a path to a block device node or
regular file. If the source path contains a ":", it needs to be escaped as "\:". The
device node or file system image file needs to follow the same rules as specified for
RootImage=. Any mounts created with this option are specific to the unit, and are not
visible in the host's mount table.

These settings may be used more than once, each usage appends to the unit's list of image
paths. If the empty string is assigned, the entire list of mount paths defined prior to
this is reset.

Each sysext image must carry a /usr/lib/extension-release.d/extension-release.IMAGE file
while each confext image must carry a /etc/extension-release.d/extension-release.IMAGE
file, with the appropriate metadata which matches RootImage=/RootDirectory= or the host.
See: os-release(5). To disable the safety check that the extension-release file name
matches the image file name, the x-systemd.relax-extension-release-check mount option may
be appended.

This option is only available for system services and is not supported for services
running in per-user instances of the service manager.

Added in version 248.

ExtensionDirectories=
This setting is similar to BindReadOnlyPaths= in that it mounts a file system hierarchy
from a directory, but instead of providing a destination path, an overlay will be set up.
This option expects a whitespace separated list of source directories.

A read-only OverlayFS will be set up on top of /usr/ and /opt/ hierarchies for sysext
images and /etc/ hierarchy for confext images. The order in which the directories are
listed will determine the order in which the overlay is laid down: directories specified
first to last will result in overlayfs layers bottom to top.

Each directory listed in ExtensionDirectories= may be prefixed with "-", in which case it
will be ignored when its source path does not exist. Any mounts created with this option
are specific to the unit, and are not visible in the host's mount table.

These settings may be used more than once, each usage appends to the unit's list of
directories paths. If the empty string is assigned, the entire list of mount paths
defined prior to this is reset.

Each sysext directory must contain a /usr/lib/extension-release.d/extension-release.IMAGE
file while each confext directory must carry a
/etc/extension-release.d/extension-release.IMAGE file, with the appropriate metadata
which matches RootImage=/RootDirectory= or the host. See: os-release(5).

Note that usage from user units requires overlayfs support in unprivileged user
namespaces, which was first introduced in kernel v5.11.

Added in version 251.

USER/GROUP IDENTITY
These options are only available for system services and are not supported for services
running in per-user instances of the service manager.

User=, Group=
Set the UNIX user or group that the processes are executed as, respectively. Takes a
single user or group name, or a numeric ID as argument. For system services (services run
by the system service manager, i.e. managed by PID 1) and for user services of the root
user (services managed by root's instance of systemd --user), the default is "root", but
User= may be used to specify a different user. For user services of any other user,
switching user identity is not permitted, hence the only valid setting is the same user
the user's service manager is running as. If no group is set, the default group of the
user is used. This setting does not affect commands whose command line is prefixed with
"+".

Note that this enforces only weak restrictions on the user/group name syntax, but will
generate warnings in many cases where user/group names do not adhere to the following
rules: the specified name should consist only of the characters a-z, A-Z, 0-9, "_" and
"-", except for the first character which must be one of a-z, A-Z and "_" (i.e. digits
and "-" are not permitted as first character). The user/group name must have at least one
character, and at most 31. These restrictions are made in order to avoid ambiguities and
to ensure user/group names and unit files remain portable among Linux systems. For
further details on the names accepted and the names warned about see User/Group Name
Syntax[3].

When used in conjunction with DynamicUser= the user/group name specified is dynamically
allocated at the time the service is started, and released at the time the service is
stopped — unless it is already allocated statically (see below). If DynamicUser= is not
used the specified user and group must have been created statically in the user database
no later than the moment the service is started, for example using the sysusers.d(5)
facility, which is applied at boot or package install time. If the user does not exist by
then program invocation will fail.

If the User= setting is used the supplementary group list is initialized from the
specified user's default group list, as defined in the system's user and group database.
Additional groups may be configured through the SupplementaryGroups= setting (see below).

DynamicUser=
Takes a boolean parameter. If set, a UNIX user and group pair is allocated dynamically
when the unit is started, and released as soon as it is stopped. The user and group will
not be added to /etc/passwd or /etc/group, but are managed transiently during runtime.
The nss-systemd(8) glibc NSS module provides integration of these dynamic users/groups
into the system's user and group databases. The user and group name to use may be
configured via User= and Group= (see above). If these options are not used and dynamic
user/group allocation is enabled for a unit, the name of the dynamic user/group is
implicitly derived from the unit name. If the unit name without the type suffix qualifies
as valid user name it is used directly, otherwise a name incorporating a hash of it is
used. If a statically allocated user or group of the configured name already exists, it
is used and no dynamic user/group is allocated. Note that if User= is specified and the
static group with the name exists, then it is required that the static user with the name
already exists. Similarly, if Group= is specified and the static user with the name
exists, then it is required that the static group with the name already exists. Dynamic
users/groups are allocated from the UID/GID range 61184...65519. It is recommended to
avoid this range for regular system or login users. At any point in time each UID/GID
from this range is only assigned to zero or one dynamically allocated users/groups in
use. However, UID/GIDs are recycled after a unit is terminated. Care should be taken that
any processes running as part of a unit for which dynamic users/groups are enabled do not
leave files or directories owned by these users/groups around, as a different unit might
get the same UID/GID assigned later on, and thus gain access to these files or
directories. If DynamicUser= is enabled, RemoveIPC= and PrivateTmp= are implied (and
cannot be turned off). This ensures that the lifetime of IPC objects and temporary files
created by the executed processes is bound to the runtime of the service, and hence the
lifetime of the dynamic user/group. Since /tmp/ and /var/tmp/ are usually the only
world-writable directories on a system this ensures that a unit making use of dynamic
user/group allocation cannot leave files around after unit termination. Furthermore
NoNewPrivileges= and RestrictSUIDSGID= are implicitly enabled (and cannot be disabled),
to ensure that processes invoked cannot take benefit or create SUID/SGID files or
directories. Moreover ProtectSystem=strict and ProtectHome=read-only are implied, thus
prohibiting the service to write to arbitrary file system locations. In order to allow
the service to write to certain directories, they have to be allow-listed using
ReadWritePaths=, but care must be taken so that UID/GID recycling doesn't create security
issues involving files created by the service. Use RuntimeDirectory= (see below) in order
to assign a writable runtime directory to a service, owned by the dynamic user/group and
removed automatically when the unit is terminated. Use StateDirectory=, CacheDirectory=
and LogsDirectory= in order to assign a set of writable directories for specific purposes
to the service in a way that they are protected from vulnerabilities due to UID reuse
(see below). If this option is enabled, care should be taken that the unit's processes do
not get access to directories outside of these explicitly configured and managed ones.
Specifically, do not use BindPaths= and be careful with AF_UNIX file descriptor passing
for directory file descriptors, as this would permit processes to create files or
directories owned by the dynamic user/group that are not subject to the lifecycle and
access guarantees of the service. Note that this option is currently incompatible with
D-Bus policies, thus a service using this option may currently not allocate a D-Bus
service name (note that this does not affect calling into other D-Bus services). Defaults
to off.

Added in version 232.

SupplementaryGroups=
Sets the supplementary Unix groups the processes are executed as. This takes a
space-separated list of group names or IDs. This option may be specified more than once,
in which case all listed groups are set as supplementary groups. When the empty string is
assigned, the list of supplementary groups is reset, and all assignments prior to this
one will have no effect. In any way, this option does not override, but extends the list
of supplementary groups configured in the system group database for the user. This does
not affect commands prefixed with "+".

SetLoginEnvironment=
Takes a boolean parameter that controls whether to set $HOME, $LOGNAME, and $SHELL
environment variables. If unset, this is controlled by whether User= is set. If true,
they will always be set for system services, i.e. even when the default user "root" is
used. If false, the mentioned variables are not set by systemd, no matter whether User=
is used or not. This option normally has no effect on user services, since these
variables are typically inherited from user manager's own environment anyway.

Added in version 255.

PAMName=
Sets the PAM service name to set up a session as. If set, the executed process will be
registered as a PAM session under the specified service name. This is only useful in
conjunction with the User= setting, and is otherwise ignored. If not set, no PAM session
will be opened for the executed processes. See pam(8) for details.

Note that for each unit making use of this option a PAM session handler process will be
maintained as part of the unit and stays around as long as the unit is active, to ensure
that appropriate actions can be taken when the unit and hence the PAM session terminates.
This process is named "(sd-pam)" and is an immediate child process of the unit's main
process.

Note that when this option is used for a unit it is very likely (depending on PAM
configuration) that the main unit process will be migrated to its own session scope unit
when it is activated. This process will hence be associated with two units: the unit it
was originally started from (and for which PAMName= was configured), and the session
scope unit. Any child processes of that process will however be associated with the
session scope unit only. This has implications when used in combination with
NotifyAccess=all, as these child processes will not be able to affect changes in the
original unit through notification messages. These messages will be considered belonging
to the session scope unit and not the original unit. It is hence not recommended to use
PAMName= in combination with NotifyAccess=all.

CAPABILITIES
These options are only available for system services, or for services running in per-user
instances of the service manager in which case PrivateUsers= is implicitly enabled (requires
unprivileged user namespaces support to be enabled in the kernel via the
"kernel.unprivileged_userns_clone=" sysctl).

CapabilityBoundingSet=
Controls which capabilities to include in the capability bounding set for the executed
process. See capabilities(7) for details. Takes a whitespace-separated list of capability
names, e.g. CAP_SYS_ADMIN, CAP_DAC_OVERRIDE, CAP_SYS_PTRACE. Capabilities listed will be
included in the bounding set, all others are removed. If the list of capabilities is
prefixed with "~", all but the listed capabilities will be included, the effect of the
assignment inverted. Note that this option also affects the respective capabilities in
the effective, permitted and inheritable capability sets. If this option is not used, the
capability bounding set is not modified on process execution, hence no limits on the
capabilities of the process are enforced. This option may appear more than once, in which
case the bounding sets are merged by OR, or by AND if the lines are prefixed with "~"
(see below). If the empty string is assigned to this option, the bounding set is reset to
the empty capability set, and all prior settings have no effect. If set to "~" (without
any further argument), the bounding set is reset to the full set of available
capabilities, also undoing any previous settings. This does not affect commands prefixed
with "+".

Use systemd-analyze(1)'s capability command to retrieve a list of capabilities defined on
the local system.

Example: if a unit has the following,

CapabilityBoundingSet=CAP_A CAP_B
CapabilityBoundingSet=CAP_B CAP_C

then CAP_A, CAP_B, and CAP_C are set. If the second line is prefixed with "~", e.g.,

CapabilityBoundingSet=CAP_A CAP_B
CapabilityBoundingSet=~CAP_B CAP_C

then, only CAP_A is set.

AmbientCapabilities=
Controls which capabilities to include in the ambient capability set for the executed
process. Takes a whitespace-separated list of capability names, e.g. CAP_SYS_ADMIN,
CAP_DAC_OVERRIDE, CAP_SYS_PTRACE. This option may appear more than once, in which case
the ambient capability sets are merged (see the above examples in
CapabilityBoundingSet=). If the list of capabilities is prefixed with "~", all but the
listed capabilities will be included, the effect of the assignment inverted. If the empty
string is assigned to this option, the ambient capability set is reset to the empty
capability set, and all prior settings have no effect. If set to "~" (without any further
argument), the ambient capability set is reset to the full set of available capabilities,
also undoing any previous settings. Note that adding capabilities to the ambient
capability set adds them to the process's inherited capability set.

Ambient capability sets are useful if you want to execute a process as a non-privileged
user but still want to give it some capabilities. Note that in this case option keep-caps
is automatically added to SecureBits= to retain the capabilities over the user change.
AmbientCapabilities= does not affect commands prefixed with "+".

Added in version 229.

SECURITY
NoNewPrivileges=
Takes a boolean argument. If true, ensures that the service process and all its children
can never gain new privileges through execve() (e.g. via setuid or setgid bits, or
filesystem capabilities). This is the simplest and most effective way to ensure that a
process and its children can never elevate privileges again. Defaults to false. In case
the service will be run in a new mount namespace anyway and SELinux is disabled, all file
systems are mounted with MS_NOSUID flag. Also see No New Privileges Flag[4].

Note that this setting only has an effect on the unit's processes themselves (or any
processes directly or indirectly forked off them). It has no effect on processes
potentially invoked on request of them through tools such as at(1), crontab(1), systemd-
run(1), or arbitrary IPC services.

Added in version 187.

SecureBits=
Controls the secure bits set for the executed process. Takes a space-separated
combination of options from the following list: keep-caps, keep-caps-locked,
no-setuid-fixup, no-setuid-fixup-locked, noroot, and noroot-locked. This option may
appear more than once, in which case the secure bits are ORed. If the empty string is
assigned to this option, the bits are reset to 0. This does not affect commands prefixed
with "+". See capabilities(7) for details.

MANDATORY ACCESS CONTROL
These options are only available for system services and are not supported for services
running in per-user instances of the service manager.

SELinuxContext=
Set the SELinux security context of the executed process. If set, this will override the
automated domain transition. However, the policy still needs to authorize the transition.
This directive is ignored if SELinux is disabled. If prefixed by "-", failing to set the
SELinux security context will be ignored, but it's still possible that the subsequent
execve() may fail if the policy doesn't allow the transition for the non-overridden
context. This does not affect commands prefixed with "+". See setexeccon(3) for details.

Added in version 209.

AppArmorProfile=
Takes a profile name as argument. The process executed by the unit will switch to this
profile when started. Profiles must already be loaded in the kernel, or the unit will
fail. If prefixed by "-", all errors will be ignored. This setting has no effect if
AppArmor is not enabled. This setting does not affect commands prefixed with "+".

Added in version 210.

SmackProcessLabel=
Takes a SMACK64 security label as argument. The process executed by the unit will be
started under this label and SMACK will decide whether the process is allowed to run or
not, based on it. The process will continue to run under the label specified here unless
the executable has its own SMACK64EXEC label, in which case the process will transition
to run under that label. When not specified, the label that systemd is running under is
used. This directive is ignored if SMACK is disabled.

The value may be prefixed by "-", in which case all errors will be ignored. An empty
value may be specified to unset previous assignments. This does not affect commands
prefixed with "+".

Added in version 218.

PROCESS PROPERTIES
LimitCPU=, LimitFSIZE=, LimitDATA=, LimitSTACK=, LimitCORE=, LimitRSS=, LimitNOFILE=,
LimitAS=, LimitNPROC=, LimitMEMLOCK=, LimitLOCKS=, LimitSIGPENDING=, LimitMSGQUEUE=,
LimitNICE=, LimitRTPRIO=, LimitRTTIME=
Set soft and hard limits on various resources for executed processes. See setrlimit(2)
for details on the process resource limit concept. Process resource limits may be
specified in two formats: either as single value to set a specific soft and hard limit to
the same value, or as colon-separated pair soft:hard to set both limits individually
(e.g. "LimitAS=4G:16G"). Use the string infinity to configure no limit on a specific
resource. The multiplicative suffixes K, M, G, T, P and E (to the base 1024) may be used
for resource limits measured in bytes (e.g. "LimitAS=16G"). For the limits referring to
time values, the usual time units ms, s, min, h and so on may be used (see
systemd.time(7) for details). Note that if no time unit is specified for LimitCPU= the
default unit of seconds is implied, while for LimitRTTIME= the default unit of
microseconds is implied. Also, note that the effective granularity of the limits might
influence their enforcement. For example, time limits specified for LimitCPU= will be
rounded up implicitly to multiples of 1s. For LimitNICE= the value may be specified in
two syntaxes: if prefixed with "+" or "-", the value is understood as regular Linux nice
value in the range -20...19. If not prefixed like this the value is understood as raw
resource limit parameter in the range 0...40 (with 0 being equivalent to 1).

Note that most process resource limits configured with these options are per-process, and
processes may fork in order to acquire a new set of resources that are accounted
independently of the original process, and may thus escape limits set. Also note that
LimitRSS= is not implemented on Linux, and setting it has no effect. Often it is
advisable to prefer the resource controls listed in systemd.resource-control(5) over
these per-process limits, as they apply to services as a whole, may be altered
dynamically at runtime, and are generally more expressive. For example, MemoryMax= is a
more powerful (and working) replacement for LimitRSS=.

Note that LimitNPROC= will limit the number of processes from one (real) UID and not the
number of processes started (forked) by the service. Therefore the limit is cumulative
for all processes running under the same UID. Please also note that the LimitNPROC= will
not be enforced if the service is running as root (and not dropping privileges). Due to
these limitations, TasksMax= (see systemd.resource-control(5)) is typically a better
choice than LimitNPROC=.

Resource limits not configured explicitly for a unit default to the value configured in
the various DefaultLimitCPU=, DefaultLimitFSIZE=, ... options available in systemd-
system.conf(5), and – if not configured there – the kernel or per-user defaults, as
defined by the OS (the latter only for user services, see below).

For system units these resource limits may be chosen freely. When these settings are
configured in a user service (i.e. a service run by the per-user instance of the service
manager) they cannot be used to raise the limits above those set for the user manager
itself when it was first invoked, as the user's service manager generally lacks the
privileges to do so. In user context these configuration options are hence only useful to
lower the limits passed in or to raise the soft limit to the maximum of the hard limit as
configured for the user. To raise the user's limits further, the available configuration
mechanisms differ between operating systems, but typically require privileges. In most
cases it is possible to configure higher per-user resource limits via PAM or by setting
limits on the system service encapsulating the user's service manager, i.e. the user's
instance of user@.service. After making such changes, make sure to restart the user's
service manager.

Table 1. Resource limit directives, their equivalent ulimit shell commands and the unit
used
┌──────────────────┬───────────────────┬─────────────────────┬──────────────────────┐
│ Directive │ ulimit equivalent │ Unit │ Notes │
├──────────────────┼───────────────────┼─────────────────────┼──────────────────────┤
│ LimitCPU= │ ulimit -t │ Seconds │ - │
├──────────────────┼───────────────────┼─────────────────────┼──────────────────────┤
│ LimitFSIZE= │ ulimit -f │ Bytes │ - │
├──────────────────┼───────────────────┼─────────────────────┼──────────────────────┤
│ LimitDATA= │ ulimit -d │ Bytes │ Don't use. This │
│ │ │ │ limits the allowed │
│ │ │ │ address range, not │
│ │ │ │ memory use! Defaults │
│ │ │ │ to unlimited and │
│ │ │ │ should not be │
│ │ │ │ lowered. To limit │
│ │ │ │ memory use, see │
│ │ │ │ MemoryMax= in │
│ │ │ │ systemd.resource- │
│ │ │ │ control(5). │
├──────────────────┼───────────────────┼─────────────────────┼──────────────────────┤
│ LimitSTACK= │ ulimit -s │ Bytes │ - │
├──────────────────┼───────────────────┼─────────────────────┼──────────────────────┤
│ LimitCORE= │ ulimit -c │ Bytes │ - │
├──────────────────┼───────────────────┼─────────────────────┼──────────────────────┤
│ LimitRSS= │ ulimit -m │ Bytes │ Don't use. No effect │
│ │ │ │ on Linux. │
├──────────────────┼───────────────────┼─────────────────────┼──────────────────────┤
│ LimitNOFILE= │ ulimit -n │ Number of File │ Don't use. Be │
│ │ │ Descriptors │ careful when raising │
│ │ │ │ the soft limit above │
│ │ │ │ 1024, since │
│ │ │ │ select(2) cannot │
│ │ │ │ function with file │
│ │ │ │ descriptors above │
│ │ │ │ 1023 on Linux. │
│ │ │ │ Nowadays, the hard │
│ │ │ │ limit defaults to │
│ │ │ │ 524288, a very high │
│ │ │ │ value compared to │
│ │ │ │ historical defaults. │
│ │ │ │ Typically │
│ │ │ │ applications should │
│ │ │ │ increase their soft │
│ │ │ │ limit to the hard │
│ │ │ │ limit on their own, │
│ │ │ │ if they are OK with │
│ │ │ │ working with file │
│ │ │ │ descriptors above │
│ │ │ │ 1023, i.e. do not │
│ │ │ │ use select(2). Note │
│ │ │ │ that file │
│ │ │ │ descriptors are │
│ │ │ │ nowadays accounted │
│ │ │ │ like any other form │
│ │ │ │ of memory, thus │
│ │ │ │ there should not be │
│ │ │ │ any need to lower │
│ │ │ │ the hard limit. Use │
│ │ │ │ MemoryMax= to │
│ │ │ │ control overall │
│ │ │ │ service memory use, │
│ │ │ │ including file │
│ │ │ │ descriptor memory. │
├──────────────────┼───────────────────┼─────────────────────┼──────────────────────┤
│ LimitAS= │ ulimit -v │ Bytes │ Don't use. This │
│ │ │ │ limits the allowed │
│ │ │ │ address range, not │
│ │ │ │ memory use! Defaults │
│ │ │ │ to unlimited and │
│ │ │ │ should not be │
│ │ │ │ lowered. To limit │
│ │ │ │ memory use, see │
│ │ │ │ MemoryMax= in │
│ │ │ │ systemd.resource- │
│ │ │ │ control(5). │
├──────────────────┼───────────────────┼─────────────────────┼──────────────────────┤
│ LimitNPROC= │ ulimit -u │ Number of Processes │ This limit is │
│ │ │ │ enforced based on │
│ │ │ │ the number of │
│ │ │ │ processes belonging │
│ │ │ │ to the user. │
│ │ │ │ Typically it's │
│ │ │ │ better to track │
│ │ │ │ processes per │
│ │ │ │ service, i.e. use │
│ │ │ │ TasksMax=, see │
│ │ │ │ systemd.resource- │
│ │ │ │ control(5). │
├──────────────────┼───────────────────┼─────────────────────┼──────────────────────┤
│ LimitMEMLOCK= │ ulimit -l │ Bytes │ - │
├──────────────────┼───────────────────┼─────────────────────┼──────────────────────┤
│ LimitLOCKS= │ ulimit -x │ Number of Locks │ - │
├──────────────────┼───────────────────┼─────────────────────┼──────────────────────┤
│ LimitSIGPENDING= │ ulimit -i │ Number of Queued │ - │
│ │ │ Signals │ │
├──────────────────┼───────────────────┼─────────────────────┼──────────────────────┤
│ LimitMSGQUEUE= │ ulimit -q │ Bytes │ - │
├──────────────────┼───────────────────┼─────────────────────┼──────────────────────┤
│ LimitNICE= │ ulimit -e │ Nice Level │ - │
├──────────────────┼───────────────────┼─────────────────────┼──────────────────────┤
│ LimitRTPRIO= │ ulimit -r │ Realtime Priority │ - │
├──────────────────┼───────────────────┼─────────────────────┼──────────────────────┤
│ LimitRTTIME= │ ulimit -R │ Microseconds │ - │
└──────────────────┴───────────────────┴─────────────────────┴──────────────────────┘

UMask=
Controls the file mode creation mask. Takes an access mode in octal notation. See
umask(2) for details. Defaults to 0022 for system units. For user units the default value
is inherited from the per-user service manager (whose default is in turn inherited from
the system service manager, and thus typically also is 0022 — unless overridden by a PAM
module). In order to change the per-user mask for all user services, consider setting the
UMask= setting of the user's user@.service system service instance. The per-user umask
may also be set via the umask field of a user's JSON User Record[5] (for users managed by
systemd-homed.service(8) this field may be controlled via homectl --umask=). It may also
be set via a PAM module, such as pam_umask(8).

CoredumpFilter=
Controls which types of memory mappings will be saved if the process dumps core (using
the /proc/pid/coredump_filter file). Takes a whitespace-separated combination of mapping
type names or numbers (with the default base 16). Mapping type names are
private-anonymous, shared-anonymous, private-file-backed, shared-file-backed,
elf-headers, private-huge, shared-huge, private-dax, shared-dax, and the special values
all (all types) and default (the kernel default of "private-anonymous shared-anonymous
elf-headers private-huge"). See core(5) for the meaning of the mapping types. When
specified multiple times, all specified masks are ORed. When not set, or if the empty
value is assigned, the inherited value is not changed.

Example 2. Add DAX pages to the dump filter

CoredumpFilter=default private-dax shared-dax

Added in version 246.

KeyringMode=
Controls how the kernel session keyring is set up for the service (see session-keyring(7)
for details on the session keyring). Takes one of inherit, private, shared. If set to
inherit no special keyring setup is done, and the kernel's default behaviour is applied.
If private is used a new session keyring is allocated when a service process is invoked,
and it is not linked up with any user keyring. This is the recommended setting for system
services, as this ensures that multiple services running under the same system user ID
(in particular the root user) do not share their key material among each other. If shared
is used a new session keyring is allocated as for private, but the user keyring of the
user configured with User= is linked into it, so that keys assigned to the user may be
requested by the unit's processes. In this mode multiple units running processes under
the same user ID may share key material. Unless inherit is selected the unique invocation
ID for the unit (see below) is added as a protected key by the name "invocation_id" to
the newly created session keyring. Defaults to private for services of the system service
manager and to inherit for non-service units and for services of the user service
manager.

Added in version 235.

OOMScoreAdjust=
Sets the adjustment value for the Linux kernel's Out-Of-Memory (OOM) killer score for
executed processes. Takes an integer between -1000 (to disable OOM killing of processes
of this unit) and 1000 (to make killing of processes of this unit under memory pressure
very likely). See The /proc Filesystem[6] for details. If not specified defaults to the
OOM score adjustment level of the service manager itself, which is normally at 0.

Use the OOMPolicy= setting of service units to configure how the service manager shall
react to the kernel OOM killer or systemd-oomd terminating a process of the service. See
systemd.service(5) for details.

TimerSlackNSec=
Sets the timer slack in nanoseconds for the executed processes. The timer slack controls
the accuracy of wake-ups triggered by timers. See prctl(2) for more information. Note
that in contrast to most other time span definitions this parameter takes an integer
value in nano-seconds if no unit is specified. The usual time units are understood too.

Personality=
Controls which kernel architecture uname(2) shall report, when invoked by unit processes.
Takes one of the architecture identifiers arm64, arm64-be, arm, arm-be, x86, x86-64, ppc,
ppc-le, ppc64, ppc64-le, s390 or s390x. Which personality architectures are supported
depends on the kernel's native architecture. Usually the 64-bit versions of the various
system architectures support their immediate 32-bit personality architecture counterpart,
but no others. For example, x86-64 systems support the x86-64 and x86 personalities but
no others. The personality feature is useful when running 32-bit services on a 64-bit
host system. If not specified, the personality is left unmodified and thus reflects the
personality of the host system's kernel. This option is not useful on architectures for
which only one native word width was ever available, such as m68k (32-bit only) or alpha
(64-bit only).

Added in version 209.

IgnoreSIGPIPE=
Takes a boolean argument. If true, SIGPIPE is ignored in the executed process. Defaults
to true since SIGPIPE is generally only useful in shell pipelines.

SCHEDULING
Nice=
Sets the default nice level (scheduling priority) for executed processes. Takes an
integer between -20 (highest priority) and 19 (lowest priority). In case of resource
contention, smaller values mean more resources will be made available to the unit's
processes, larger values mean less resources will be made available. See setpriority(2)
for details.

CPUSchedulingPolicy=
Sets the CPU scheduling policy for executed processes. Takes one of other, batch, idle,
fifo or rr. See sched_setscheduler(2) for details.

CPUSchedulingPriority=
Sets the CPU scheduling priority for executed processes. The available priority range
depends on the selected CPU scheduling policy (see above). For real-time scheduling
policies an integer between 1 (lowest priority) and 99 (highest priority) can be used. In
case of CPU resource contention, smaller values mean less CPU time is made available to
the service, larger values mean more. See sched_setscheduler(2) for details.

CPUSchedulingResetOnFork=
Takes a boolean argument. If true, elevated CPU scheduling priorities and policies will
be reset when the executed processes call fork(2), and can hence not leak into child
processes. See sched_setscheduler(2) for details. Defaults to false.

CPUAffinity=
Controls the CPU affinity of the executed processes. Takes a list of CPU indices or
ranges separated by either whitespace or commas. Alternatively, takes a special "numa"
value in which case systemd automatically derives allowed CPU range based on the value of
NUMAMask= option. CPU ranges are specified by the lower and upper CPU indices separated
by a dash. This option may be specified more than once, in which case the specified CPU
affinity masks are merged. If the empty string is assigned, the mask is reset, all
assignments prior to this will have no effect. See sched_setaffinity(2) for details.

NUMAPolicy=
Controls the NUMA memory policy of the executed processes. Takes a policy type, one of:
default, preferred, bind, interleave and local. A list of NUMA nodes that should be
associated with the policy must be specified in NUMAMask=. For more details on each
policy please see, set_mempolicy(2). For overall overview of NUMA support in Linux see,
numa(7).

Added in version 243.

NUMAMask=
Controls the NUMA node list which will be applied alongside with selected NUMA policy.
Takes a list of NUMA nodes and has the same syntax as a list of CPUs for CPUAffinity=
option or special "all" value which will include all available NUMA nodes in the mask.
Note that the list of NUMA nodes is not required for default and local policies and for
preferred policy we expect a single NUMA node.

Added in version 243.

IOSchedulingClass=
Sets the I/O scheduling class for executed processes. Takes one of the strings realtime,
best-effort or idle. The kernel's default scheduling class is best-effort at a priority
of 4. If the empty string is assigned to this option, all prior assignments to both
IOSchedulingClass= and IOSchedulingPriority= have no effect. See ioprio_set(2) for
details.

IOSchedulingPriority=
Sets the I/O scheduling priority for executed processes. Takes an integer between 0
(highest priority) and 7 (lowest priority). In case of I/O contention, smaller values
mean more I/O bandwidth is made available to the unit's processes, larger values mean
less bandwidth. The available priorities depend on the selected I/O scheduling class (see
above). If the empty string is assigned to this option, all prior assignments to both
IOSchedulingClass= and IOSchedulingPriority= have no effect. For the kernel's default
scheduling class (best-effort) this defaults to 4. See ioprio_set(2) for details.

SANDBOXING
The following sandboxing options are an effective way to limit the exposure of the system
towards the unit's processes. It is recommended to turn on as many of these options for each
unit as is possible without negatively affecting the process' ability to operate. Note that
many of these sandboxing features are gracefully turned off on systems where the underlying
security mechanism is not available. For example, ProtectSystem= has no effect if the kernel
is built without file system namespacing or if the service manager runs in a container
manager that makes file system namespacing unavailable to its payload. Similarly,
RestrictRealtime= has no effect on systems that lack support for SECCOMP system call
filtering, or in containers where support for this is turned off.

Also note that some sandboxing functionality is generally not available in user services
(i.e. services run by the per-user service manager). Specifically, the various settings
requiring file system namespacing support (such as ProtectSystem=) are not available, as the
underlying kernel functionality is only accessible to privileged processes. However, most
namespacing settings, that will not work on their own in user services, will work when used
in conjunction with PrivateUsers=true.

ProtectSystem=
Takes a boolean argument or the special values "full" or "strict". If true, mounts the
/usr/ and the boot loader directories (/boot and /efi) read-only for processes invoked by
this unit. If set to "full", the /etc/ directory is mounted read-only, too. If set to
"strict" the entire file system hierarchy is mounted read-only, except for the API file
system subtrees /dev/, /proc/ and /sys/ (protect these directories using PrivateDevices=,
ProtectKernelTunables=, ProtectControlGroups=). This setting ensures that any
modification of the vendor-supplied operating system (and optionally its configuration,
and local mounts) is prohibited for the service. It is recommended to enable this setting
for all long-running services, unless they are involved with system updates or need to
modify the operating system in other ways. If this option is used, ReadWritePaths= may be
used to exclude specific directories from being made read-only. This setting is implied
if DynamicUser= is set. This setting cannot ensure protection in all cases. In general it
has the same limitations as ReadOnlyPaths=, see below. Defaults to off.

Added in version 214.

ProtectHome=
Takes a boolean argument or the special values "read-only" or "tmpfs". If true, the
directories /home/, /root, and /run/user are made inaccessible and empty for processes
invoked by this unit. If set to "read-only", the three directories are made read-only
instead. If set to "tmpfs", temporary file systems are mounted on the three directories
in read-only mode. The value "tmpfs" is useful to hide home directories not relevant to
the processes invoked by the unit, while still allowing necessary directories to be made
visible when listed in BindPaths= or BindReadOnlyPaths=.

Setting this to "yes" is mostly equivalent to setting the three directories in
InaccessiblePaths=. Similarly, "read-only" is mostly equivalent to ReadOnlyPaths=, and
"tmpfs" is mostly equivalent to TemporaryFileSystem= with ":ro".

It is recommended to enable this setting for all long-running services (in particular
network-facing ones), to ensure they cannot get access to private user data, unless the
services actually require access to the user's private data. This setting is implied if
DynamicUser= is set. This setting cannot ensure protection in all cases. In general it
has the same limitations as ReadOnlyPaths=, see below.

Added in version 214.

RuntimeDirectory=, StateDirectory=, CacheDirectory=, LogsDirectory=, ConfigurationDirectory=
These options take a whitespace-separated list of directory names. The specified
directory names must be relative, and may not include "..". If set, when the unit is
started, one or more directories by the specified names will be created (including their
parents) below the locations defined in the following table. Also, the corresponding
environment variable will be defined with the full paths of the directories. If multiple
directories are set, then in the environment variable the paths are concatenated with
colon (":").

Table 2. Automatic directory creation and environment variables
┌─────────────────────────┬────────────────┬──────────────────────┬──────────────────────────┐
│ Directory │ Below path for │ Below path for user │ Environment variable │
│ │ system units │ units │ set │
├─────────────────────────┼────────────────┼──────────────────────┼──────────────────────────┤
│ RuntimeDirectory= │ /run/ │ $XDG_RUNTIME_DIR │ $RUNTIME_DIRECTORY │
├─────────────────────────┼────────────────┼──────────────────────┼──────────────────────────┤
│ StateDirectory= │ /var/lib/ │ $XDG_STATE_HOME │ $STATE_DIRECTORY │
├─────────────────────────┼────────────────┼──────────────────────┼──────────────────────────┤
│ CacheDirectory= │ /var/cache/ │ $XDG_CACHE_HOME │ $CACHE_DIRECTORY │
├─────────────────────────┼────────────────┼──────────────────────┼──────────────────────────┤
│ LogsDirectory= │ /var/log/ │ $XDG_STATE_HOME/log/ │ $LOGS_DIRECTORY │
├─────────────────────────┼────────────────┼──────────────────────┼──────────────────────────┤
│ ConfigurationDirectory= │ /etc/ │ $XDG_CONFIG_HOME │ $CONFIGURATION_DIRECTORY │
└─────────────────────────┴────────────────┴──────────────────────┴──────────────────────────┘

In case of RuntimeDirectory= the innermost subdirectories are removed when the unit is
stopped. It is possible to preserve the specified directories in this case if
RuntimeDirectoryPreserve= is configured to restart or yes (see below). The directories
specified with StateDirectory=, CacheDirectory=, LogsDirectory=, ConfigurationDirectory=
are not removed when the unit is stopped.

Except in case of ConfigurationDirectory=, the innermost specified directories will be
owned by the user and group specified in User= and Group=. If the specified directories
already exist and their owning user or group do not match the configured ones, all files
and directories below the specified directories as well as the directories themselves
will have their file ownership recursively changed to match what is configured. As an
optimization, if the specified directories are already owned by the right user and group,
files and directories below of them are left as-is, even if they do not match what is
requested. The innermost specified directories will have their access mode adjusted to
the what is specified in RuntimeDirectoryMode=, StateDirectoryMode=, CacheDirectoryMode=,
LogsDirectoryMode= and ConfigurationDirectoryMode=.

These options imply BindPaths= for the specified paths. When combined with RootDirectory=
or RootImage= these paths always reside on the host and are mounted from there into the
unit's file system namespace.

If DynamicUser= is used, the logic for CacheDirectory=, LogsDirectory= and
StateDirectory= is slightly altered: the directories are created below
/var/cache/private, /var/log/private and /var/lib/private, respectively, which are host
directories made inaccessible to unprivileged users, which ensures that access to these
directories cannot be gained through dynamic user ID recycling. Symbolic links are
created to hide this difference in behaviour. Both from perspective of the host and from
inside the unit, the relevant directories hence always appear directly below /var/cache,
/var/log and /var/lib.

Use RuntimeDirectory= to manage one or more runtime directories for the unit and bind
their lifetime to the daemon runtime. This is particularly useful for unprivileged
daemons that cannot create runtime directories in /run/ due to lack of privileges, and to
make sure the runtime directory is cleaned up automatically after use. For runtime
directories that require more complex or different configuration or lifetime guarantees,
please consider using tmpfiles.d(5).

RuntimeDirectory=, StateDirectory=, CacheDirectory= and LogsDirectory= optionally support
a second parameter, separated by ":". The second parameter will be interpreted as a
destination path that will be created as a symlink to the directory. The symlinks will be
created after any BindPaths= or TemporaryFileSystem= options have been set up, to make
ephemeral symlinking possible. The same source can have multiple symlinks, by using the
same first parameter, but a different second parameter.

The directories defined by these options are always created under the standard paths used
by systemd (/var/, /run/, /etc/, ...). If the service needs directories in a different
location, a different mechanism has to be used to create them.

tmpfiles.d(5) provides functionality that overlaps with these options. Using these
options is recommended, because the lifetime of the directories is tied directly to the
lifetime of the unit, and it is not necessary to ensure that the tmpfiles.d configuration
is executed before the unit is started.

To remove any of the directories created by these settings, use the systemctl clean ...
command on the relevant units, see systemctl(1) for details.

Example: if a system service unit has the following,

RuntimeDirectory=foo/bar baz

the service manager creates /run/foo (if it does not exist), /run/foo/bar, and /run/baz.
The directories /run/foo/bar and /run/baz except /run/foo are owned by the user and group
specified in User= and Group=, and removed when the service is stopped.

Example: if a system service unit has the following,

RuntimeDirectory=foo/bar
StateDirectory=aaa/bbb ccc

then the environment variable "RUNTIME_DIRECTORY" is set with "/run/foo/bar", and
"STATE_DIRECTORY" is set with "/var/lib/aaa/bbb:/var/lib/ccc".

Example: if a system service unit has the following,

RuntimeDirectory=foo:bar foo:baz

the service manager creates /run/foo (if it does not exist), and /run/bar plus /run/baz
as symlinks to /run/foo.

Added in version 211.

RuntimeDirectoryMode=, StateDirectoryMode=, CacheDirectoryMode=, LogsDirectoryMode=,
ConfigurationDirectoryMode=
Specifies the access mode of the directories specified in RuntimeDirectory=,
StateDirectory=, CacheDirectory=, LogsDirectory=, or ConfigurationDirectory=,
respectively, as an octal number. Defaults to 0755. See "Permissions" in
path_resolution(7) for a discussion of the meaning of permission bits.

Added in version 234.

RuntimeDirectoryPreserve=
Takes a boolean argument or restart. If set to no (the default), the directories
specified in RuntimeDirectory= are always removed when the service stops. If set to
restart the directories are preserved when the service is both automatically and manually
restarted. Here, the automatic restart means the operation specified in Restart=, and
manual restart means the one triggered by systemctl restart foo.service. If set to yes,
then the directories are not removed when the service is stopped. Note that since the
runtime directory /run/ is a mount point of "tmpfs", then for system services the
directories specified in RuntimeDirectory= are removed when the system is rebooted.

Added in version 235.

TimeoutCleanSec=
Configures a timeout on the clean-up operation requested through systemctl clean ..., see
systemctl(1) for details. Takes the usual time values and defaults to infinity, i.e. by
default no timeout is applied. If a timeout is configured the clean operation will be
aborted forcibly when the timeout is reached, potentially leaving resources on disk.

Added in version 244.

ReadWritePaths=, ReadOnlyPaths=, InaccessiblePaths=, ExecPaths=, NoExecPaths=
Sets up a new file system namespace for executed processes. These options may be used to
limit access a process has to the file system. Each setting takes a space-separated list
of paths relative to the host's root directory (i.e. the system running the service
manager). Note that if paths contain symlinks, they are resolved relative to the root
directory set with RootDirectory=/RootImage=.

Paths listed in ReadWritePaths= are accessible from within the namespace with the same
access modes as from outside of it. Paths listed in ReadOnlyPaths= are accessible for
reading only, writing will be refused even if the usual file access controls would permit
this. Nest ReadWritePaths= inside of ReadOnlyPaths= in order to provide writable
subdirectories within read-only directories. Use ReadWritePaths= in order to allow-list
specific paths for write access if ProtectSystem=strict is used. Note that
ReadWritePaths= cannot be used to gain write access to a file system whose superblock is
mounted read-only. On Linux, for each mount point write access is granted only if the
mount point itself and the file system superblock backing it are not marked read-only.
ReadWritePaths= only controls the former, not the latter, hence a read-only file system
superblock remains protected.

Paths listed in InaccessiblePaths= will be made inaccessible for processes inside the
namespace along with everything below them in the file system hierarchy. This may be more
restrictive than desired, because it is not possible to nest ReadWritePaths=,
ReadOnlyPaths=, BindPaths=, or BindReadOnlyPaths= inside it. For a more flexible option,
see TemporaryFileSystem=.

Content in paths listed in NoExecPaths= are not executable even if the usual file access
controls would permit this. Nest ExecPaths= inside of NoExecPaths= in order to provide
executable content within non-executable directories.

Non-directory paths may be specified as well. These options may be specified more than
once, in which case all paths listed will have limited access from within the namespace.
If the empty string is assigned to this option, the specific list is reset, and all prior
assignments have no effect.

Paths in ReadWritePaths=, ReadOnlyPaths=, InaccessiblePaths=, ExecPaths= and NoExecPaths=
may be prefixed with "-", in which case they will be ignored when they do not exist. If
prefixed with "+" the paths are taken relative to the root directory of the unit, as
configured with RootDirectory=/RootImage=, instead of relative to the root directory of
the host (see above). When combining "-" and "+" on the same path make sure to specify
"-" first, and "+" second.

Note that these settings will disconnect propagation of mounts from the unit's processes
to the host. This means that this setting may not be used for services which shall be
able to install mount points in the main mount namespace. For ReadWritePaths= and
ReadOnlyPaths=, propagation in the other direction is not affected, i.e. mounts created
on the host generally appear in the unit processes' namespace, and mounts removed on the
host also disappear there too. In particular, note that mount propagation from host to
unit will result in unmodified mounts to be created in the unit's namespace, i.e.
writable mounts appearing on the host will be writable in the unit's namespace too, even
when propagated below a path marked with ReadOnlyPaths=! Restricting access with these
options hence does not extend to submounts of a directory that are created later on. This
means the lock-down offered by that setting is not complete, and does not offer full
protection.

Note that the effect of these settings may be undone by privileged processes. In order to
set up an effective sandboxed environment for a unit it is thus recommended to combine
these settings with either CapabilityBoundingSet=~CAP_SYS_ADMIN or
SystemCallFilter=~@mount.

Please be extra careful when applying these options to API file systems (a list of them
could be found in MountAPIVPS=), since they may be required for basic system
functionalities. Moreover, /run/ needs to be writable for setting up mount namespace and
propagation.

Simple allow-list example using these directives:

[Service]
ReadOnlyPaths=/
ReadWritePaths=/var /run
InaccessiblePaths=-/lost+found
NoExecPaths=/
ExecPaths=/usr/sbin/my_daemon /usr/lib /usr/lib64

These options are only available for system services, or for services running in per-user
instances of the service manager in which case PrivateUsers= is implicitly enabled
(requires unprivileged user namespaces support to be enabled in the kernel via the
"kernel.unprivileged_userns_clone=" sysctl).

Added in version 231.

TemporaryFileSystem=
Takes a space-separated list of mount points for temporary file systems (tmpfs). If set,
a new file system namespace is set up for executed processes, and a temporary file system
is mounted on each mount point. This option may be specified more than once, in which
case temporary file systems are mounted on all listed mount points. If the empty string
is assigned to this option, the list is reset, and all prior assignments have no effect.
Each mount point may optionally be suffixed with a colon (":") and mount options such as
"size=10%" or "ro". By default, each temporary file system is mounted with
"nodev,strictatime,mode=0755". These can be disabled by explicitly specifying the
corresponding mount options, e.g., "dev" or "nostrictatime".

This is useful to hide files or directories not relevant to the processes invoked by the
unit, while necessary files or directories can be still accessed by combining with
BindPaths= or BindReadOnlyPaths=:

Example: if a unit has the following,

TemporaryFileSystem=/var:ro
BindReadOnlyPaths=/var/lib/systemd

then the invoked processes by the unit cannot see any files or directories under /var/
except for /var/lib/systemd or its contents.

Added in version 238.

PrivateTmp=
Takes a boolean argument. If true, sets up a new file system namespace for the executed
processes and mounts private /tmp/ and /var/tmp/ directories inside it that are not
shared by processes outside of the namespace. This is useful to secure access to
temporary files of the process, but makes sharing between processes via /tmp/ or
/var/tmp/ impossible. If true, all temporary files created by a service in these
directories will be removed after the service is stopped. Defaults to false. It is
possible to run two or more units within the same private /tmp/ and /var/tmp/ namespace
by using the JoinsNamespaceOf= directive, see systemd.unit(5) for details. This setting
is implied if DynamicUser= is set. For this setting, the same restrictions regarding
mount propagation and privileges apply as for ReadOnlyPaths= and related calls, see
above. Enabling this setting has the side effect of adding Requires= and After=
dependencies on all mount units necessary to access /tmp/ and /var/tmp/. Moreover an
implicitly After= ordering on systemd-tmpfiles-setup.service(8) is added.

Note that the implementation of this setting might be impossible (for example if mount
namespaces are not available), and the unit should be written in a way that does not
solely rely on this setting for security.

PrivateDevices=
Takes a boolean argument. If true, sets up a new /dev/ mount for the executed processes
and only adds API pseudo devices such as /dev/null, /dev/zero or /dev/random (as well as
the pseudo TTY subsystem) to it, but no physical devices such as /dev/sda, system memory
/dev/mem, system ports /dev/port and others. This is useful to turn off physical device
access by the executed process. Defaults to false.

Enabling this option will install a system call filter to block low-level I/O system
calls that are grouped in the @raw-io set, remove CAP_MKNOD and CAP_SYS_RAWIO from the
capability bounding set for the unit, and set DevicePolicy=closed (see systemd.resource-
control(5) for details). Note that using this setting will disconnect propagation of
mounts from the service to the host (propagation in the opposite direction continues to
work). This means that this setting may not be used for services which shall be able to
install mount points in the main mount namespace. The new /dev/ will be mounted read-only
and 'noexec'. The latter may break old programs which try to set up executable memory by
using mmap(2) of /dev/zero instead of using MAP_ANON. For this setting the same
restrictions regarding mount propagation and privileges apply as for ReadOnlyPaths= and
related calls, see above.

When access to some but not all devices must be possible, the DeviceAllow= setting might
be used instead. See systemd.resource-control(5).

Added in version 209.

PrivateNetwork=
Takes a boolean argument. If true, sets up a new network namespace for the executed
processes and configures only the loopback network device "lo" inside it. No other
network devices will be available to the executed process. This is useful to turn off
network access by the executed process. Defaults to false. It is possible to run two or
more units within the same private network namespace by using the JoinsNamespaceOf=
directive, see systemd.unit(5) for details. Note that this option will disconnect all
socket families from the host, including AF_NETLINK and AF_UNIX. Effectively, for
AF_NETLINK this means that device configuration events received from systemd-
udevd.service(8) are not delivered to the unit's processes. And for AF_UNIX this has the
effect that AF_UNIX sockets in the abstract socket namespace of the host will become
unavailable to the unit's processes (however, those located in the file system will
continue to be accessible).

Note that the implementation of this setting might be impossible (for example if network
namespaces are not available), and the unit should be written in a way that does not
solely rely on this setting for security.

When this option is enabled, PrivateMounts= is implied unless it is explicitly disabled,
and /sys will be remounted to associate it with the new network namespace.

When this option is used on a socket unit any sockets bound on behalf of this unit will
be bound within a private network namespace. This may be combined with JoinsNamespaceOf=
to listen on sockets inside of network namespaces of other services.

NetworkNamespacePath=
Takes an absolute file system path referring to a Linux network namespace pseudo-file
(i.e. a file like /proc/$PID/ns/net or a bind mount or symlink to one). When set the
invoked processes are added to the network namespace referenced by that path. The path
has to point to a valid namespace file at the moment the processes are forked off. If
this option is used PrivateNetwork= has no effect. If this option is used together with
JoinsNamespaceOf= then it only has an effect if this unit is started before any of the
listed units that have PrivateNetwork= or NetworkNamespacePath= configured, as otherwise
the network namespace of those units is reused.

When this option is enabled, PrivateMounts= is implied unless it is explicitly disabled,
and /sys will be remounted to associate it with the new network namespace.

When this option is used on a socket unit any sockets bound on behalf of this unit will
be bound within the specified network namespace.

Added in version 242.

PrivateIPC=
Takes a boolean argument. If true, sets up a new IPC namespace for the executed
processes. Each IPC namespace has its own set of System V IPC identifiers and its own
POSIX message queue file system. This is useful to avoid name clash of IPC identifiers.
Defaults to false. It is possible to run two or more units within the same private IPC
namespace by using the JoinsNamespaceOf= directive, see systemd.unit(5) for details.

Note that IPC namespacing does not have an effect on AF_UNIX sockets, which are the most
common form of IPC used on Linux. Instead, AF_UNIX sockets in the file system are subject
to mount namespacing, and those in the abstract namespace are subject to network
namespacing. IPC namespacing only has an effect on SysV IPC (which is mostly legacy) as
well as POSIX message queues (for which AF_UNIX/SOCK_SEQPACKET sockets are typically a
better replacement). IPC namespacing also has no effect on POSIX shared memory (which is
subject to mount namespacing) either. See ipc_namespaces(7) for the details.

Note that the implementation of this setting might be impossible (for example if IPC
namespaces are not available), and the unit should be written in a way that does not
solely rely on this setting for security.

Added in version 248.

IPCNamespacePath=
Takes an absolute file system path referring to a Linux IPC namespace pseudo-file (i.e. a
file like /proc/$PID/ns/ipc or a bind mount or symlink to one). When set the invoked
processes are added to the network namespace referenced by that path. The path has to
point to a valid namespace file at the moment the processes are forked off. If this
option is used PrivateIPC= has no effect. If this option is used together with
JoinsNamespaceOf= then it only has an effect if this unit is started before any of the
listed units that have PrivateIPC= or IPCNamespacePath= configured, as otherwise the
network namespace of those units is reused.

Added in version 248.

MemoryKSM=
Takes a boolean argument. When set, it enables KSM (kernel samepage merging) for the
processes. KSM is a memory-saving de-duplication feature. Anonymous memory pages with
identical content can be replaced by a single write-protected page. This feature should
only be enabled for jobs that share the same security domain. For details, see Kernel
Samepage Merging[7] in the kernel documentation.

Note that this functionality might not be available, for example if KSM is disabled in
the kernel, or the kernel doesn't support controlling KSM at the process level through
prctl(2).

Added in version 254.

PrivateUsers=
Takes a boolean argument. If true, sets up a new user namespace for the executed
processes and configures a minimal user and group mapping, that maps the "root" user and
group as well as the unit's own user and group to themselves and everything else to the
"nobody" user and group. This is useful to securely detach the user and group databases
used by the unit from the rest of the system, and thus to create an effective sandbox
environment. All files, directories, processes, IPC objects and other resources owned by
users/groups not equaling "root" or the unit's own will stay visible from within the unit
but appear owned by the "nobody" user and group. If this mode is enabled, all unit
processes are run without privileges in the host user namespace (regardless if the unit's
own user/group is "root" or not). Specifically this means that the process will have zero
process capabilities on the host's user namespace, but full capabilities within the
service's user namespace. Settings such as CapabilityBoundingSet= will affect only the
latter, and there's no way to acquire additional capabilities in the host's user
namespace. Defaults to off.

When this setting is set up by a per-user instance of the service manager, the mapping of
the "root" user and group to itself is omitted (unless the user manager is root).
Additionally, in the per-user instance manager case, the user namespace will be set up
before most other namespaces. This means that combining PrivateUsers=true with other
namespaces will enable use of features not normally supported by the per-user instances
of the service manager.

This setting is particularly useful in conjunction with RootDirectory=/RootImage=, as the
need to synchronize the user and group databases in the root directory and on the host is
reduced, as the only users and groups who need to be matched are "root", "nobody" and the
unit's own user and group.

Note that the implementation of this setting might be impossible (for example if user
namespaces are not available), and the unit should be written in a way that does not
solely rely on this setting for security.

Added in version 232.

ProtectHostname=
Takes a boolean argument. When set, sets up a new UTS namespace for the executed
processes. In addition, changing hostname or domainname is prevented. Defaults to off.

Note that the implementation of this setting might be impossible (for example if UTS
namespaces are not available), and the unit should be written in a way that does not
solely rely on this setting for security.

Note that when this option is enabled for a service hostname changes no longer propagate
from the system into the service, it is hence not suitable for services that need to take
notice of system hostname changes dynamically.

Added in version 242.

ProtectClock=
Takes a boolean argument. If set, writes to the hardware clock or system clock will be
denied. Defaults to off. Enabling this option removes CAP_SYS_TIME and CAP_WAKE_ALARM
from the capability bounding set for this unit, installs a system call filter to block
calls that can set the clock, and DeviceAllow=char-rtc r is implied. Note that the system
calls are blocked altogether, the filter does not take into account that some of the
calls can be used to read the clock state with some parameter combinations. Effectively,
/dev/rtc0, /dev/rtc1, etc. are made read-only to the service. See systemd.resource-
control(5) for the details about DeviceAllow=.

It is recommended to turn this on for most services that do not need modify the clock or
check its state.

Added in version 245.

ProtectKernelTunables=
Takes a boolean argument. If true, kernel variables accessible through /proc/sys/, /sys/,
/proc/sysrq-trigger, /proc/latency_stats, /proc/acpi, /proc/timer_stats, /proc/fs and
/proc/irq will be made read-only to all processes of the unit. Usually, tunable kernel
variables should be initialized only at boot-time, for example with the sysctl.d(5)
mechanism. Few services need to write to these at runtime; it is hence recommended to
turn this on for most services. For this setting the same restrictions regarding mount
propagation and privileges apply as for ReadOnlyPaths= and related calls, see above.
Defaults to off. Note that this option does not prevent indirect changes to kernel
tunables effected by IPC calls to other processes. However, InaccessiblePaths= may be
used to make relevant IPC file system objects inaccessible. If ProtectKernelTunables= is
set, MountAPIVFS=yes is implied.

Added in version 232.

ProtectKernelModules=
Takes a boolean argument. If true, explicit module loading will be denied. This allows
module load and unload operations to be turned off on modular kernels. It is recommended
to turn this on for most services that do not need special file systems or extra kernel
modules to work. Defaults to off. Enabling this option removes CAP_SYS_MODULE from the
capability bounding set for the unit, and installs a system call filter to block module
system calls, also /usr/lib/modules is made inaccessible. For this setting the same
restrictions regarding mount propagation and privileges apply as for ReadOnlyPaths= and
related calls, see above. Note that limited automatic module loading due to user
configuration or kernel mapping tables might still happen as side effect of requested
user operations, both privileged and unprivileged. To disable module auto-load feature
please see sysctl.d(5) kernel.modules_disabled mechanism and
/proc/sys/kernel/modules_disabled documentation.

Added in version 232.

ProtectKernelLogs=
Takes a boolean argument. If true, access to the kernel log ring buffer will be denied.
It is recommended to turn this on for most services that do not need to read from or
write to the kernel log ring buffer. Enabling this option removes CAP_SYSLOG from the
capability bounding set for this unit, and installs a system call filter to block the
syslog(2) system call (not to be confused with the libc API syslog(3) for userspace
logging). The kernel exposes its log buffer to userspace via /dev/kmsg and /proc/kmsg. If
enabled, these are made inaccessible to all the processes in the unit.

Added in version 244.

ProtectControlGroups=
Takes a boolean argument. If true, the Linux Control Groups (cgroups(7)) hierarchies
accessible through /sys/fs/cgroup/ will be made read-only to all processes of the unit.
Except for container managers no services should require write access to the control
groups hierarchies; it is hence recommended to turn this on for most services. For this
setting the same restrictions regarding mount propagation and privileges apply as for
ReadOnlyPaths= and related calls, see above. Defaults to off. If ProtectControlGroups= is
set, MountAPIVFS=yes is implied.

This option is only available for system services and is not supported for services
running in per-user instances of the service manager.

Added in version 232.

RestrictAddressFamilies=
Restricts the set of socket address families accessible to the processes of this unit.
Takes "none", or a space-separated list of address family names to allow-list, such as
AF_UNIX, AF_INET or AF_INET6. When "none" is specified, then all address families will be
denied. When prefixed with "~" the listed address families will be applied as deny list,
otherwise as allow list. Note that this restricts access to the socket(2) system call
only. Sockets passed into the process by other means (for example, by using socket
activation with socket units, see systemd.socket(5)) are unaffected. Also, sockets
created with socketpair() (which creates connected AF_UNIX sockets only) are unaffected.
Note that this option has no effect on 32-bit x86, s390, s390x, mips, mips-le, ppc,
ppc-le, ppc64, ppc64-le and is ignored (but works correctly on other ABIs, including
x86-64). Note that on systems supporting multiple ABIs (such as x86/x86-64) it is
recommended to turn off alternative ABIs for services, so that they cannot be used to
circumvent the restrictions of this option. Specifically, it is recommended to combine
this option with SystemCallArchitectures=native or similar. By default, no restrictions
apply, all address families are accessible to processes. If assigned the empty string,
any previous address family restriction changes are undone. This setting does not affect
commands prefixed with "+".

Use this option to limit exposure of processes to remote access, in particular via exotic
and sensitive network protocols, such as AF_PACKET. Note that in most cases, the local
AF_UNIX address family should be included in the configured allow list as it is
frequently used for local communication, including for syslog(2) logging.

Added in version 211.

RestrictFileSystems=
Restricts the set of filesystems processes of this unit can open files on. Takes a
space-separated list of filesystem names. Any filesystem listed is made accessible to the
unit's processes, access to filesystem types not listed is prohibited (allow-listing). If
the first character of the list is "~", the effect is inverted: access to the filesystems
listed is prohibited (deny-listing). If the empty string is assigned, access to
filesystems is not restricted.

If you specify both types of this option (i.e. allow-listing and deny-listing), the first
encountered will take precedence and will dictate the default action (allow access to the
filesystem or deny it). Then the next occurrences of this option will add or delete the
listed filesystems from the set of the restricted filesystems, depending on its type and
the default action.

Example: if a unit has the following,

RestrictFileSystems=ext4 tmpfs
RestrictFileSystems=ext2 ext4

then access to ext4, tmpfs, and ext2 is allowed and access to other filesystems is
denied.

Example: if a unit has the following,

RestrictFileSystems=ext4 tmpfs
RestrictFileSystems=~ext4

then only access tmpfs is allowed.

Example: if a unit has the following,

RestrictFileSystems=~ext4 tmpfs
RestrictFileSystems=ext4

then only access to tmpfs is denied.

As the number of possible filesystems is large, predefined sets of filesystems are
provided. A set starts with "@" character, followed by name of the set.

Table 3. Currently predefined filesystem sets
┌───────────────────┬───────────────────────────────────┐
│ Set │ Description │
├───────────────────┼───────────────────────────────────┤
│ @basic-api │ Basic filesystem API. │
├───────────────────┼───────────────────────────────────┤
│ @auxiliary-api │ Auxiliary filesystem API. │
├───────────────────┼───────────────────────────────────┤
│ @common-block │ Common block device filesystems. │
├───────────────────┼───────────────────────────────────┤
│ @historical-block │ Historical block device │
│ │ filesystems. │
├───────────────────┼───────────────────────────────────┤
│ @network │ Well-known network filesystems. │
├───────────────────┼───────────────────────────────────┤
│ @privileged-api │ Privileged filesystem API. │
├───────────────────┼───────────────────────────────────┤
│ @temporary │ Temporary filesystems: tmpfs, │
│ │ ramfs. │
├───────────────────┼───────────────────────────────────┤
│ @known │ All known filesystems defined by │
│ │ the kernel. This list is defined │
│ │ statically in systemd based on a │
│ │ kernel version that was available │
│ │ when this systemd version was │
│ │ released. It will become │
│ │ progressively more out-of-date as │
│ │ the kernel is updated. │
└───────────────────┴───────────────────────────────────┘

Use systemd-analyze(1)'s filesystems command to retrieve a list of filesystems defined on
the local system.

Note that this setting might not be supported on some systems (for example if the LSM
eBPF hook is not enabled in the underlying kernel or if not using the unified control
group hierarchy). In that case this setting has no effect.

This option cannot be bypassed by prefixing "+" to the executable path in the service
unit, as it applies to the whole control group.

Added in version 250.

RestrictNamespaces=
Restricts access to Linux namespace functionality for the processes of this unit. For
details about Linux namespaces, see namespaces(7). Either takes a boolean argument, or a
space-separated list of namespace type identifiers. If false (the default), no
restrictions on namespace creation and switching are made. If true, access to any kind of
namespacing is prohibited. Otherwise, a space-separated list of namespace type
identifiers must be specified, consisting of any combination of: cgroup, ipc, net, mnt,
pid, user and uts. Any namespace type listed is made accessible to the unit's processes,
access to namespace types not listed is prohibited (allow-listing). By prepending the
list with a single tilde character ("~") the effect may be inverted: only the listed
namespace types will be made inaccessible, all unlisted ones are permitted
(deny-listing). If the empty string is assigned, the default namespace restrictions are
applied, which is equivalent to false. This option may appear more than once, in which
case the namespace types are merged by OR, or by AND if the lines are prefixed with "~"
(see examples below). Internally, this setting limits access to the unshare(2), clone(2)
and setns(2) system calls, taking the specified flags parameters into account. Note that
— if this option is used — in addition to restricting creation and switching of the
specified types of namespaces (or all of them, if true) access to the setns() system call
with a zero flags parameter is prohibited. This setting is only supported on x86, x86-64,
mips, mips-le, mips64, mips64-le, mips64-n32, mips64-le-n32, ppc64, ppc64-le, s390 and
s390x, and enforces no restrictions on other architectures.

Example: if a unit has the following,

RestrictNamespaces=cgroup ipc
RestrictNamespaces=cgroup net

then cgroup, ipc, and net are set. If the second line is prefixed with "~", e.g.,

RestrictNamespaces=cgroup ipc
RestrictNamespaces=~cgroup net

then, only ipc is set.

Added in version 233.

LockPersonality=
Takes a boolean argument. If set, locks down the personality(2) system call so that the
kernel execution domain may not be changed from the default or the personality selected
with Personality= directive. This may be useful to improve security, because odd
personality emulations may be poorly tested and source of vulnerabilities.

Added in version 235.

MemoryDenyWriteExecute=
Takes a boolean argument. If set, attempts to create memory mappings that are writable
and executable at the same time, or to change existing memory mappings to become
executable, or mapping shared memory segments as executable, are prohibited.
Specifically, a system call filter is added (or preferably, an equivalent kernel check is
enabled with prctl(2)) that rejects mmap(2) system calls with both PROT_EXEC and
PROT_WRITE set, mprotect(2) or pkey_mprotect(2) system calls with PROT_EXEC set and
shmat(2) system calls with SHM_EXEC set. Note that this option is incompatible with
programs and libraries that generate program code dynamically at runtime, including JIT
execution engines, executable stacks, and code "trampoline" feature of various C
compilers. This option improves service security, as it makes harder for software
exploits to change running code dynamically. However, the protection can be circumvented,
if the service can write to a filesystem, which is not mounted with noexec (such as
/dev/shm), or it can use memfd_create(). This can be prevented by making such file
systems inaccessible to the service (e.g. InaccessiblePaths=/dev/shm) and installing
further system call filters (SystemCallFilter=~memfd_create). Note that this feature is
fully available on x86-64, and partially on x86. Specifically, the shmat() protection is
not available on x86. Note that on systems supporting multiple ABIs (such as x86/x86-64)
it is recommended to turn off alternative ABIs for services, so that they cannot be used
to circumvent the restrictions of this option. Specifically, it is recommended to combine
this option with SystemCallArchitectures=native or similar.

Added in version 231.

RestrictRealtime=
Takes a boolean argument. If set, any attempts to enable realtime scheduling in a process
of the unit are refused. This restricts access to realtime task scheduling policies such
as SCHED_FIFO, SCHED_RR or SCHED_DEADLINE. See sched(7) for details about these
scheduling policies. Realtime scheduling policies may be used to monopolize CPU time for
longer periods of time, and may hence be used to lock up or otherwise trigger
Denial-of-Service situations on the system. It is hence recommended to restrict access to
realtime scheduling to the few programs that actually require them. Defaults to off.

Added in version 231.

RestrictSUIDSGID=
Takes a boolean argument. If set, any attempts to set the set-user-ID (SUID) or
set-group-ID (SGID) bits on files or directories will be denied (for details on these
bits see inode(7)). As the SUID/SGID bits are mechanisms to elevate privileges, and allow
users to acquire the identity of other users, it is recommended to restrict creation of
SUID/SGID files to the few programs that actually require them. Note that this restricts
marking of any type of file system object with these bits, including both regular files
and directories (where the SGID is a different meaning than for files, see
documentation). This option is implied if DynamicUser= is enabled. Defaults to off.

Added in version 242.

RemoveIPC=
Takes a boolean parameter. If set, all System V and POSIX IPC objects owned by the user
and group the processes of this unit are run as are removed when the unit is stopped.
This setting only has an effect if at least one of User=, Group= and DynamicUser= are
used. It has no effect on IPC objects owned by the root user. Specifically, this removes
System V semaphores, as well as System V and POSIX shared memory segments and message
queues. If multiple units use the same user or group the IPC objects are removed when the
last of these units is stopped. This setting is implied if DynamicUser= is set.

This option is only available for system services and is not supported for services
running in per-user instances of the service manager.

Added in version 232.

PrivateMounts=
Takes a boolean parameter. If set, the processes of this unit will be run in their own
private file system (mount) namespace with all mount propagation from the processes
towards the host's main file system namespace turned off. This means any file system
mount points established or removed by the unit's processes will be private to them and
not be visible to the host. However, file system mount points established or removed on
the host will be propagated to the unit's processes. See mount_namespaces(7) for details
on file system namespaces. Defaults to off.

When turned on, this executes three operations for each invoked process: a new
CLONE_NEWNS namespace is created, after which all existing mounts are remounted to
MS_SLAVE to disable propagation from the unit's processes to the host (but leaving
propagation in the opposite direction in effect). Finally, the mounts are remounted again
to the propagation mode configured with MountFlags=, see below.

File system namespaces are set up individually for each process forked off by the service
manager. Mounts established in the namespace of the process created by ExecStartPre= will
hence be cleaned up automatically as soon as that process exits and will not be available
to subsequent processes forked off for ExecStart= (and similar applies to the various
other commands configured for units). Similarly, JoinsNamespaceOf= does not permit
sharing kernel mount namespaces between units, it only enables sharing of the /tmp/ and
/var/tmp/ directories.

Other file system namespace unit settings — PrivateMounts=, PrivateTmp=, PrivateDevices=,
ProtectSystem=, ProtectHome=, ReadOnlyPaths=, InaccessiblePaths=, ReadWritePaths=, ... —
also enable file system namespacing in a fashion equivalent to this option. Hence it is
primarily useful to explicitly request this behaviour if none of the other settings are
used.

Added in version 239.

MountFlags=
Takes a mount propagation setting: shared, slave or private, which controls whether file
system mount points in the file system namespaces set up for this unit's processes will
receive or propagate mounts and unmounts from other file system namespaces. See mount(2)
for details on mount propagation, and the three propagation flags in particular.

This setting only controls the final propagation setting in effect on all mount points of
the file system namespace created for each process of this unit. Other file system
namespacing unit settings (see the discussion in PrivateMounts= above) will implicitly
disable mount and unmount propagation from the unit's processes towards the host by
changing the propagation setting of all mount points in the unit's file system namespace
to slave first. Setting this option to shared does not reestablish propagation in that
case.

If not set – but file system namespaces are enabled through another file system namespace
unit setting – shared mount propagation is used, but — as mentioned — as slave is applied
first, propagation from the unit's processes to the host is still turned off.

It is not recommended to use private mount propagation for units, as this means temporary
mounts (such as removable media) of the host will stay mounted and thus indefinitely busy
in forked off processes, as unmount propagation events won't be received by the file
system namespace of the unit.

Usually, it is best to leave this setting unmodified, and use higher level file system
namespacing options instead, in particular PrivateMounts=, see above.

SYSTEM CALL FILTERING
SystemCallFilter=
Takes a space-separated list of system call names. If this setting is used, all system
calls executed by the unit processes except for the listed ones will result in immediate
process termination with the SIGSYS signal (allow-listing). (See SystemCallErrorNumber=
below for changing the default action). If the first character of the list is "~", the
effect is inverted: only the listed system calls will result in immediate process
termination (deny-listing). Deny-listed system calls and system call groups may
optionally be suffixed with a colon (":") and "errno" error number (between 0 and 4095)
or errno name such as EPERM, EACCES or EUCLEAN (see errno(3) for a full list). This value
will be returned when a deny-listed system call is triggered, instead of terminating the
processes immediately. Special setting "kill" can be used to explicitly specify killing.
This value takes precedence over the one given in SystemCallErrorNumber=, see below. This
feature makes use of the Secure Computing Mode 2 interfaces of the kernel ('seccomp
filtering') and is useful for enforcing a minimal sandboxing environment. Note that the
execve(), exit(), exit_group(), getrlimit(), rt_sigreturn(), sigreturn() system calls and
the system calls for querying time and sleeping are implicitly allow-listed and do not
need to be listed explicitly. This option may be specified more than once, in which case
the filter masks are merged. If the empty string is assigned, the filter is reset, all
prior assignments will have no effect. This does not affect commands prefixed with "+".

Note that on systems supporting multiple ABIs (such as x86/x86-64) it is recommended to
turn off alternative ABIs for services, so that they cannot be used to circumvent the
restrictions of this option. Specifically, it is recommended to combine this option with
SystemCallArchitectures=native or similar.

Note that strict system call filters may impact execution and error handling code paths
of the service invocation. Specifically, access to the execve() system call is required
for the execution of the service binary — if it is blocked service invocation will
necessarily fail. Also, if execution of the service binary fails for some reason (for
example: missing service executable), the error handling logic might require access to an
additional set of system calls in order to process and log this failure correctly. It
might be necessary to temporarily disable system call filters in order to simplify
debugging of such failures.

If you specify both types of this option (i.e. allow-listing and deny-listing), the first
encountered will take precedence and will dictate the default action (termination or
approval of a system call). Then the next occurrences of this option will add or delete
the listed system calls from the set of the filtered system calls, depending of its type
and the default action. (For example, if you have started with an allow list rule for
read() and write(), and right after it add a deny list rule for write(), then write()
will be removed from the set.)

As the number of possible system calls is large, predefined sets of system calls are
provided. A set starts with "@" character, followed by name of the set.

Table 4. Currently predefined system call sets
┌─────────────────┬───────────────────────────────────┐
│ Set │ Description │
├─────────────────┼───────────────────────────────────┤
│ @aio │ Asynchronous I/O (io_setup(2), │
│ │ io_submit(2), and related calls) │
├─────────────────┼───────────────────────────────────┤
│ @basic-io │ System calls for basic I/O: │
│ │ reading, writing, seeking, file │
│ │ descriptor duplication and │
│ │ closing (read(2), write(2), and │
│ │ related calls) │
├─────────────────┼───────────────────────────────────┤
│ @chown │ Changing file ownership │
│ │ (chown(2), fchownat(2), and │
│ │ related calls) │
├─────────────────┼───────────────────────────────────┤
│ @clock │ System calls for changing the │
│ │ system clock (adjtimex(2), │
│ │ settimeofday(2), and related │
│ │ calls) │
├─────────────────┼───────────────────────────────────┤
│ @cpu-emulation │ System calls for CPU emulation │
│ │ functionality (vm86(2) and │
│ │ related calls) │
├─────────────────┼───────────────────────────────────┤
│ @debug │ Debugging, performance monitoring │
│ │ and tracing functionality │
│ │ (ptrace(2), perf_event_open(2) │
│ │ and related calls) │
├─────────────────┼───────────────────────────────────┤
│ @file-system │ File system operations: opening, │
│ │ creating files and directories │
│ │ for read and write, renaming and │
│ │ removing them, reading file │
│ │ properties, or creating hard and │
│ │ symbolic links │
├─────────────────┼───────────────────────────────────┤
│ @io-event │ Event loop system calls (poll(2), │
│ │ select(2), epoll(7), eventfd(2) │
│ │ and related calls) │
├─────────────────┼───────────────────────────────────┤
│ @ipc │ Pipes, SysV IPC, POSIX Message │
│ │ Queues and other IPC │
│ │ (mq_overview(7), svipc(7)) │
├─────────────────┼───────────────────────────────────┤
│ @keyring │ Kernel keyring access (keyctl(2) │
│ │ and related calls) │
├─────────────────┼───────────────────────────────────┤
│ @memlock │ Locking of memory in RAM │
│ │ (mlock(2), mlockall(2) and │
│ │ related calls) │
├─────────────────┼───────────────────────────────────┤
│ @module │ Loading and unloading of kernel │
│ │ modules (init_module(2), │
│ │ delete_module(2) and related │
│ │ calls) │
├─────────────────┼───────────────────────────────────┤
│ @mount │ Mounting and unmounting of file │
│ │ systems (mount(2), chroot(2), and │
│ │ related calls) │
├─────────────────┼───────────────────────────────────┤
│ @network-io │ Socket I/O (including local │
│ │ AF_UNIX): socket(7), unix(7) │
├─────────────────┼───────────────────────────────────┤
│ @obsolete │ Unusual, obsolete or │
│ │ unimplemented (create_module(2), │
│ │ gtty(2), ...) │
├─────────────────┼───────────────────────────────────┤
│ @pkey │ System calls that deal with │
│ │ memory protection keys (pkeys(7)) │
├─────────────────┼───────────────────────────────────┤
│ @privileged │ All system calls which need │
│ │ super-user capabilities │
│ │ (capabilities(7)) │
├─────────────────┼───────────────────────────────────┤
│ @process │ Process control, execution, │
│ │ namespacing operations (clone(2), │
│ │ kill(2), namespaces(7), ...) │
├─────────────────┼───────────────────────────────────┤
│ @raw-io │ Raw I/O port access (ioperm(2), │
│ │ iopl(2), pciconfig_read(), ...) │
├─────────────────┼───────────────────────────────────┤
│ @reboot │ System calls for rebooting and │
│ │ reboot preparation (reboot(2), │
│ │ kexec(), ...) │
├─────────────────┼───────────────────────────────────┤
│ @resources │ System calls for changing │
│ │ resource limits, memory and │
│ │ scheduling parameters │
│ │ (setrlimit(2), setpriority(2), │
│ │ ...) │
├─────────────────┼───────────────────────────────────┤
│ @sandbox │ System calls for sandboxing │
│ │ programs (seccomp(2), Landlock │
│ │ system calls, ...) │
├─────────────────┼───────────────────────────────────┤
│ @setuid │ System calls for changing user ID │
│ │ and group ID credentials, │
│ │ (setuid(2), setgid(2), │
│ │ setresuid(2), ...) │
├─────────────────┼───────────────────────────────────┤
│ @signal │ System calls for manipulating and │
│ │ handling process signals │
│ │ (signal(2), sigprocmask(2), ...) │
├─────────────────┼───────────────────────────────────┤
│ @swap │ System calls for │
│ │ enabling/disabling swap devices │
│ │ (swapon(2), swapoff(2)) │
├─────────────────┼───────────────────────────────────┤
│ @sync │ Synchronizing files and memory to │
│ │ disk (fsync(2), msync(2), and │
│ │ related calls) │
├─────────────────┼───────────────────────────────────┤
│ @system-service │ A reasonable set of system calls │
│ │ used by common system services, │
│ │ excluding any special purpose │
│ │ calls. This is the recommended │
│ │ starting point for allow-listing │
│ │ system calls for system services, │
│ │ as it contains what is typically │
│ │ needed by system services, but │
│ │ excludes overly specific │
│ │ interfaces. For example, the │
│ │ following APIs are excluded: │
│ │ "@clock", "@mount", "@swap", │
│ │ "@reboot". │
├─────────────────┼───────────────────────────────────┤
│ @timer │ System calls for scheduling │
│ │ operations by time (alarm(2), │
│ │ timer_create(2), ...) │
├─────────────────┼───────────────────────────────────┤
│ @known │ All system calls defined by the │
│ │ kernel. This list is defined │
│ │ statically in systemd based on a │
│ │ kernel version that was available │
│ │ when this systemd version was │
│ │ released. It will become │
│ │ progressively more out-of-date as │
│ │ the kernel is updated. │
└─────────────────┴───────────────────────────────────┘

Note, that as new system calls are added to the kernel, additional system calls might be
added to the groups above. Contents of the sets may also change between systemd versions.
In addition, the list of system calls depends on the kernel version and architecture for
which systemd was compiled. Use systemd-analyze syscall-filter to list the actual list of
system calls in each filter.

Generally, allow-listing system calls (rather than deny-listing) is the safer mode of
operation. It is recommended to enforce system call allow lists for all long-running
system services. Specifically, the following lines are a relatively safe basic choice for
the majority of system services:

[Service]
SystemCallFilter=@system-service
SystemCallErrorNumber=EPERM

Note that various kernel system calls are defined redundantly: there are multiple system
calls for executing the same operation. For example, the pidfd_send_signal() system call
may be used to execute operations similar to what can be done with the older kill()
system call, hence blocking the latter without the former only provides weak protection.
Since new system calls are added regularly to the kernel as development progresses,
keeping system call deny lists comprehensive requires constant work. It is thus
recommended to use allow-listing instead, which offers the benefit that new system calls
are by default implicitly blocked until the allow list is updated.

Also note that a number of system calls are required to be accessible for the dynamic
linker to work. The dynamic linker is required for running most regular programs
(specifically: all dynamic ELF binaries, which is how most distributions build packaged
programs). This means that blocking these system calls (which include open(), openat() or
mmap()) will make most programs typically shipped with generic distributions unusable.

It is recommended to combine the file system namespacing related options with
SystemCallFilter=~@mount, in order to prohibit the unit's processes to undo the mappings.
Specifically these are the options PrivateTmp=, PrivateDevices=, ProtectSystem=,
ProtectHome=, ProtectKernelTunables=, ProtectControlGroups=, ProtectKernelLogs=,
ProtectClock=, ReadOnlyPaths=, InaccessiblePaths= and ReadWritePaths=.

Added in version 187.

SystemCallErrorNumber=
Takes an "errno" error number (between 1 and 4095) or errno name such as EPERM, EACCES or
EUCLEAN, to return when the system call filter configured with SystemCallFilter= is
triggered, instead of terminating the process immediately. See errno(3) for a full list
of error codes. When this setting is not used, or when the empty string or the special
setting "kill" is assigned, the process will be terminated immediately when the filter is
triggered.

Added in version 209.

SystemCallArchitectures=
Takes a space-separated list of architecture identifiers to include in the system call
filter. The known architecture identifiers are the same as for ConditionArchitecture=
described in systemd.unit(5), as well as x32, mips64-n32, mips64-le-n32, and the special
identifier native. The special identifier native implicitly maps to the native
architecture of the system (or more precisely: to the architecture the system manager is
compiled for). By default, this option is set to the empty list, i.e. no filtering is
applied.

If this setting is used, processes of this unit will only be permitted to call native
system calls, and system calls of the specified architectures. For the purposes of this
option, the x32 architecture is treated as including x86-64 system calls. However, this
setting still fulfills its purpose, as explained below, on x32.

System call filtering is not equally effective on all architectures. For example, on x86
filtering of network socket-related calls is not possible, due to ABI limitations — a
limitation that x86-64 does not have, however. On systems supporting multiple ABIs at the
same time — such as x86/x86-64 — it is hence recommended to limit the set of permitted
system call architectures so that secondary ABIs may not be used to circumvent the
restrictions applied to the native ABI of the system. In particular, setting
SystemCallArchitectures=native is a good choice for disabling non-native ABIs.

System call architectures may also be restricted system-wide via the
SystemCallArchitectures= option in the global configuration. See systemd-system.conf(5)
for details.

Added in version 209.

SystemCallLog=
Takes a space-separated list of system call names. If this setting is used, all system
calls executed by the unit processes for the listed ones will be logged. If the first
character of the list is "~", the effect is inverted: all system calls except the listed
system calls will be logged. This feature makes use of the Secure Computing Mode 2
interfaces of the kernel ('seccomp filtering') and is useful for auditing or setting up a
minimal sandboxing environment. This option may be specified more than once, in which
case the filter masks are merged. If the empty string is assigned, the filter is reset,
all prior assignments will have no effect. This does not affect commands prefixed with
"+".

Added in version 247.

ENVIRONMENT
Environment=
Sets environment variables for executed processes. Each line is unquoted using the rules
described in "Quoting" section in systemd.syntax(7) and becomes a list of variable
assignments. If you need to assign a value containing spaces or the equals sign to a
variable, put quotes around the whole assignment. Variable expansion is not performed
inside the strings and the "$" character has no special meaning. Specifier expansion is
performed, see the "Specifiers" section in systemd.unit(5).

This option may be specified more than once, in which case all listed variables will be
set. If the same variable is listed twice, the later setting will override the earlier
setting. If the empty string is assigned to this option, the list of environment
variables is reset, all prior assignments have no effect.

The names of the variables can contain ASCII letters, digits, and the underscore
character. Variable names cannot be empty or start with a digit. In variable values, most
characters are allowed, but non-printable characters are currently rejected.

Example:

Environment="VAR1=word1 word2" VAR2=word3 "VAR3=$word 5 6"

gives three variables "VAR1", "VAR2", "VAR3" with the values "word1 word2", "word3",
"$word 5 6".

See environ(7) for details about environment variables.

Note that environment variables are not suitable for passing secrets (such as passwords,
key material, ...) to service processes. Environment variables set for a unit are exposed
to unprivileged clients via D-Bus IPC, and generally not understood as being data that
requires protection. Moreover, environment variables are propagated down the process
tree, including across security boundaries (such as setuid/setgid executables), and hence
might leak to processes that should not have access to the secret data. Use
LoadCredential=, LoadCredentialEncrypted= or SetCredentialEncrypted= (see below) to pass
data to unit processes securely.

EnvironmentFile=
Similar to Environment=, but reads the environment variables from a text file. The text
file should contain newline-separated variable assignments. Empty lines, lines without an
"=" separator, or lines starting with ";" or "#" will be ignored, which may be used for
commenting. The file must be encoded with UTF-8. Valid characters are unicode scalar
values[8] other than unicode noncharacters[9], U+0000 NUL, and U+FEFF unicode byte order
mark[10]. Control codes other than NUL are allowed.

In the file, an unquoted value after the "=" is parsed with the same backslash-escape
rules as POSIX shell unquoted text[11], but unlike in a shell, interior whitespace is
preserved and quotes after the first non-whitespace character are preserved. Leading and
trailing whitespace (space, tab, carriage return) is discarded, but interior whitespace
within the line is preserved verbatim. A line ending with a backslash will be continued
to the following one, with the newline itself discarded. A backslash "\" followed by any
character other than newline will preserve the following character, so that "\\" will
become the value "\".

In the file, a "'"-quoted value after the "=" can span multiple lines and contain any
character verbatim other than single quote, like POSIX shell single-quoted text[12]. No
backslash-escape sequences are recognized. Leading and trailing whitespace outside of the
single quotes is discarded.

In the file, a """-quoted value after the "=" can span multiple lines, and the same
escape sequences are recognized as in POSIX shell double-quoted text[13]. Backslash ("\")
followed by any of ""\`$" will preserve that character. A backslash followed by newline
is a line continuation, and the newline itself is discarded. A backslash followed by any
other character is ignored; both the backslash and the following character are preserved
verbatim. Leading and trailing whitespace outside of the double quotes is discarded.

The argument passed should be an absolute filename or wildcard expression, optionally
prefixed with "-", which indicates that if the file does not exist, it will not be read
and no error or warning message is logged. This option may be specified more than once in
which case all specified files are read. If the empty string is assigned to this option,
the list of file to read is reset, all prior assignments have no effect.

The files listed with this directive will be read shortly before the process is executed
(more specifically, after all processes from a previous unit state terminated. This means
you can generate these files in one unit state, and read it with this option in the next.
The files are read from the file system of the service manager, before any file system
changes like bind mounts take place).

Settings from these files override settings made with Environment=. If the same variable
is set twice from these files, the files will be read in the order they are specified and
the later setting will override the earlier setting.

PassEnvironment=
Pass environment variables set for the system service manager to executed processes.
Takes a space-separated list of variable names. This option may be specified more than
once, in which case all listed variables will be passed. If the empty string is assigned
to this option, the list of environment variables to pass is reset, all prior assignments
have no effect. Variables specified that are not set for the system manager will not be
passed and will be silently ignored. Note that this option is only relevant for the
system service manager, as system services by default do not automatically inherit any
environment variables set for the service manager itself. However, in case of the user
service manager all environment variables are passed to the executed processes anyway,
hence this option is without effect for the user service manager.

Variables set for invoked processes due to this setting are subject to being overridden
by those configured with Environment= or EnvironmentFile=.

Example:

PassEnvironment=VAR1 VAR2 VAR3

passes three variables "VAR1", "VAR2", "VAR3" with the values set for those variables in
PID1.

See environ(7) for details about environment variables.

Added in version 228.

UnsetEnvironment=
Explicitly unset environment variable assignments that would normally be passed from the
service manager to invoked processes of this unit. Takes a space-separated list of
variable names or variable assignments. This option may be specified more than once, in
which case all listed variables/assignments will be unset. If the empty string is
assigned to this option, the list of environment variables/assignments to unset is reset.
If a variable assignment is specified (that is: a variable name, followed by "=",
followed by its value), then any environment variable matching this precise assignment is
removed. If a variable name is specified (that is a variable name without any following
"=" or value), then any assignment matching the variable name, regardless of its value is
removed. Note that the effect of UnsetEnvironment= is applied as final step when the
environment list passed to executed processes is compiled. That means it may undo
assignments from any configuration source, including assignments made through
Environment= or EnvironmentFile=, inherited from the system manager's global set of
environment variables, inherited via PassEnvironment=, set by the service manager itself
(such as $NOTIFY_SOCKET and such), or set by a PAM module (in case PAMName= is used).

See "Environment Variables in Spawned Processes" below for a description of how those
settings combine to form the inherited environment. See environ(7) for general
information about environment variables.

Added in version 235.

LOGGING AND STANDARD INPUT/OUTPUT
StandardInput=
Controls where file descriptor 0 (STDIN) of the executed processes is connected to. Takes
one of null, tty, tty-force, tty-fail, data, file:path, socket or fd:name.

If null is selected, standard input will be connected to /dev/null, i.e. all read
attempts by the process will result in immediate EOF.

If tty is selected, standard input is connected to a TTY (as configured by TTYPath=, see
below) and the executed process becomes the controlling process of the terminal. If the
terminal is already being controlled by another process, the executed process waits until
the current controlling process releases the terminal.

tty-force is similar to tty, but the executed process is forcefully and immediately made
the controlling process of the terminal, potentially removing previous controlling
processes from the terminal.

tty-fail is similar to tty, but if the terminal already has a controlling process
start-up of the executed process fails.

The data option may be used to configure arbitrary textual or binary data to pass via
standard input to the executed process. The data to pass is configured via
StandardInputText=/StandardInputData= (see below). Note that the actual file descriptor
type passed (memory file, regular file, UNIX pipe, ...) might depend on the kernel and
available privileges. In any case, the file descriptor is read-only, and when read
returns the specified data followed by EOF.

The file:path option may be used to connect a specific file system object to standard
input. An absolute path following the ":" character is expected, which may refer to a
regular file, a FIFO or special file. If an AF_UNIX socket in the file system is
specified, a stream socket is connected to it. The latter is useful for connecting
standard input of processes to arbitrary system services.

The socket option is valid in socket-activated services only, and requires the relevant
socket unit file (see systemd.socket(5) for details) to have Accept=yes set, or to
specify a single socket only. If this option is set, standard input will be connected to
the socket the service was activated from, which is primarily useful for compatibility
with daemons designed for use with the traditional inetd(8) socket activation daemon
($LISTEN_FDS (and related) environment variables are not passed when socket value is
configured).

The fd:name option connects standard input to a specific, named file descriptor provided
by a socket unit. The name may be specified as part of this option, following a ":"
character (e.g. "fd:foobar"). If no name is specified, the name "stdin" is implied (i.e.
"fd" is equivalent to "fd:stdin"). At least one socket unit defining the specified name
must be provided via the Sockets= option, and the file descriptor name may differ from
the name of its containing socket unit. If multiple matches are found, the first one will
be used. See FileDescriptorName= in systemd.socket(5) for more details about named file
descriptors and their ordering.

This setting defaults to null, unless StandardInputText=/StandardInputData= are set, in
which case it defaults to data.

StandardOutput=
Controls where file descriptor 1 (stdout) of the executed processes is connected to.
Takes one of inherit, null, tty, journal, kmsg, journal+console, kmsg+console, file:path,
append:path, truncate:path, socket or fd:name.

inherit duplicates the file descriptor of standard input for standard output.

null connects standard output to /dev/null, i.e. everything written to it will be lost.

tty connects standard output to a tty (as configured via TTYPath=, see below). If the TTY
is used for output only, the executed process will not become the controlling process of
the terminal, and will not fail or wait for other processes to release the terminal.

journal connects standard output with the journal, which is accessible via journalctl(1).
Note that everything that is written to kmsg (see below) is implicitly stored in the
journal as well, the specific option listed below is hence a superset of this one. (Also
note that any external, additional syslog daemons receive their log data from the
journal, too, hence this is the option to use when logging shall be processed with such a
daemon.)

kmsg connects standard output with the kernel log buffer which is accessible via
dmesg(1), in addition to the journal. The journal daemon might be configured to send all
logs to kmsg anyway, in which case this option is no different from journal.

journal+console and kmsg+console work in a similar way as the two options above but copy
the output to the system console as well.

The file:path option may be used to connect a specific file system object to standard
output. The semantics are similar to the same option of StandardInput=, see above. If
path refers to a regular file on the filesystem, it is opened (created if it doesn't
exist yet) for writing at the beginning of the file, but without truncating it. If
standard input and output are directed to the same file path, it is opened only once —
for reading as well as writing — and duplicated. This is particularly useful when the
specified path refers to an AF_UNIX socket in the file system, as in that case only a
single stream connection is created for both input and output.

append:path is similar to file:path above, but it opens the file in append mode.

truncate:path is similar to file:path above, but it truncates the file when opening it.
For units with multiple command lines, e.g. Type=oneshot services with multiple
ExecStart=, or services with ExecCondition=, ExecStartPre= or ExecStartPost=, the output
file is reopened and therefore re-truncated for each command line. If the output file is
truncated while another process still has the file open, e.g. by an ExecReload= running
concurrently with an ExecStart=, and the other process continues writing to the file
without adjusting its offset, then the space between the file pointers of the two
processes may be filled with NUL bytes, producing a sparse file. Thus, truncate:path is
typically only useful for units where only one process runs at a time, such as services
with a single ExecStart= and no ExecStartPost=, ExecReload=, ExecStop= or similar.

socket connects standard output to a socket acquired via socket activation. The semantics
are similar to the same option of StandardInput=, see above.

The fd:name option connects standard output to a specific, named file descriptor provided
by a socket unit. A name may be specified as part of this option, following a ":"
character (e.g. "fd:foobar"). If no name is specified, the name "stdout" is implied
(i.e. "fd" is equivalent to "fd:stdout"). At least one socket unit defining the
specified name must be provided via the Sockets= option, and the file descriptor name may
differ from the name of its containing socket unit. If multiple matches are found, the
first one will be used. See FileDescriptorName= in systemd.socket(5) for more details
about named descriptors and their ordering.

If the standard output (or error output, see below) of a unit is connected to the journal
or the kernel log buffer, the unit will implicitly gain a dependency of type After= on
systemd-journald.socket (also see the "Implicit Dependencies" section above). Also note
that in this case stdout (or stderr, see below) will be an AF_UNIX stream socket, and not
a pipe or FIFO that can be re-opened. This means when executing shell scripts the
construct echo "hello" > /dev/stderr for writing text to stderr will not work. To
mitigate this use the construct echo "hello" >&2 instead, which is mostly equivalent and
avoids this pitfall.

If StandardInput= is set to one of tty, tty-force, tty-fail, socket, or fd:name, this
setting defaults to inherit.

In other cases, this setting defaults to the value set with DefaultStandardOutput= in
systemd-system.conf(5), which defaults to journal. Note that setting this parameter might
result in additional dependencies to be added to the unit (see above).

StandardError=
Controls where file descriptor 2 (stderr) of the executed processes is connected to. The
available options are identical to those of StandardOutput=, with some exceptions: if set
to inherit the file descriptor used for standard output is duplicated for standard error,
while fd:name will use a default file descriptor name of "stderr".

This setting defaults to the value set with DefaultStandardError= in systemd-
system.conf(5), which defaults to inherit. Note that setting this parameter might result
in additional dependencies to be added to the unit (see above).

StandardInputText=, StandardInputData=
Configures arbitrary textual or binary data to pass via file descriptor 0 (STDIN) to the
executed processes. These settings have no effect unless StandardInput= is set to data
(which is the default if StandardInput= is not set otherwise, but
StandardInputText=/StandardInputData= is). Use this option to embed process input data
directly in the unit file.

StandardInputText= accepts arbitrary textual data. C-style escapes for special characters
as well as the usual "%"-specifiers are resolved. Each time this setting is used the
specified text is appended to the per-unit data buffer, followed by a newline character
(thus every use appends a new line to the end of the buffer). Note that leading and
trailing whitespace of lines configured with this option is removed. If an empty line is
specified the buffer is cleared (hence, in order to insert an empty line, add an
additional "\n" to the end or beginning of a line).

StandardInputData= accepts arbitrary binary data, encoded in Base64[14]. No escape
sequences or specifiers are resolved. Any whitespace in the encoded version is ignored
during decoding.

Note that StandardInputText= and StandardInputData= operate on the same data buffer, and
may be mixed in order to configure both binary and textual data for the same input
stream. The textual or binary data is joined strictly in the order the settings appear in
the unit file. Assigning an empty string to either will reset the data buffer.

Please keep in mind that in order to maintain readability long unit file settings may be
split into multiple lines, by suffixing each line (except for the last) with a "\"
character (see systemd.unit(5) for details). This is particularly useful for large data
configured with these two options. Example:

...
StandardInput=data
StandardInputData=V2XigLJyZSBubyBzdHJhbmdlcnMgdG8gbG92ZQpZb3Uga25vdyB0aGUgcnVsZXMgYW5kIHNvIGRv \
IEkKQSBmdWxsIGNvbW1pdG1lbnQncyB3aGF0IEnigLJtIHRoaW5raW5nIG9mCllvdSB3b3VsZG4n \
dCBnZXQgdGhpcyBmcm9tIGFueSBvdGhlciBndXkKSSBqdXN0IHdhbm5hIHRlbGwgeW91IGhvdyBJ \
J20gZmVlbGluZwpHb3R0YSBtYWtlIHlvdSB1bmRlcnN0YW5kCgpOZXZlciBnb25uYSBnaXZlIHlv \
dSB1cApOZXZlciBnb25uYSBsZXQgeW91IGRvd24KTmV2ZXIgZ29ubmEgcnVuIGFyb3VuZCBhbmQg \
ZGVzZXJ0IHlvdQpOZXZlciBnb25uYSBtYWtlIHlvdSBjcnkKTmV2ZXIgZ29ubmEgc2F5IGdvb2Ri \
eWUKTmV2ZXIgZ29ubmEgdGVsbCBhIGxpZSBhbmQgaHVydCB5b3UK
...

Added in version 236.

LogLevelMax=
Configures filtering by log level of log messages generated by this unit. Takes a syslog
log level, one of emerg (lowest log level, only highest priority messages), alert, crit,
err, warning, notice, info, debug (highest log level, also lowest priority messages). See
syslog(3) for details. By default no filtering is applied (i.e. the default maximum log
level is debug). Use this option to configure the logging system to drop log messages of
a specific service above the specified level. For example, set LogLevelMax=info in order
to turn off debug logging of a particularly chatty unit. Note that the configured level
is applied to any log messages written by any of the processes belonging to this unit, as
well as any log messages written by the system manager process (PID 1) in reference to
this unit, sent via any supported logging protocol. The filtering is applied early in the
logging pipeline, before any kind of further processing is done. Moreover, messages which
pass through this filter successfully might still be dropped by filters applied at a
later stage in the logging subsystem. For example, MaxLevelStore= configured in
journald.conf(5) might prohibit messages of higher log levels to be stored on disk, even
though the per-unit LogLevelMax= permitted it to be processed.

Added in version 236.

LogExtraFields=
Configures additional log metadata fields to include in all log records generated by
processes associated with this unit, including systemd. This setting takes one or more
journal field assignments in the format "FIELD=VALUE" separated by whitespace. See
systemd.journal-fields(7) for details on the journal field concept. Even though the
underlying journal implementation permits binary field values, this setting accepts only
valid UTF-8 values. To include space characters in a journal field value, enclose the
assignment in double quotes ("). The usual specifiers are expanded in all assignments
(see below). Note that this setting is not only useful for attaching additional metadata
to log records of a unit, but given that all fields and values are indexed may also be
used to implement cross-unit log record matching. Assign an empty string to reset the
list.

Added in version 236.

LogRateLimitIntervalSec=, LogRateLimitBurst=
Configures the rate limiting that is applied to log messages generated by this unit. If,
in the time interval defined by LogRateLimitIntervalSec=, more messages than specified in
LogRateLimitBurst= are logged by a service, all further messages within the interval are
dropped until the interval is over. A message about the number of dropped messages is
generated. The time specification for LogRateLimitIntervalSec= may be specified in the
following units: "s", "min", "h", "ms", "us". See systemd.time(7) for details. The
default settings are set by RateLimitIntervalSec= and RateLimitBurst= configured in
journald.conf(5). Note that this only applies to log messages that are processed by the
logging subsystem, i.e. by systemd-journald.service(8). This means that if you connect a
service's stderr directly to a file via StandardOutput=file:... or a similar setting,
the rate limiting will not be applied to messages written that way (but it will be
enforced for messages generated via syslog(3) and similar functions).

Added in version 240.

LogFilterPatterns=
Define an extended regular expression to filter log messages based on the MESSAGE= field
of the structured message. If the first character of the pattern is "~", log entries
matching the pattern should be discarded. This option takes a single pattern as an
argument but can be used multiple times to create a list of allowed and denied patterns.
If the empty string is assigned, the filter is reset, and all prior assignments will have
no effect.

Because the "~" character is used to define denied patterns, it must be replaced with
"\x7e" to allow a message starting with "~". For example, "~foobar" would add a pattern
matching "foobar" to the deny list, while "\x7efoobar" would add a pattern matching
"~foobar" to the allow list.

Log messages are tested against denied patterns (if any), then against allowed patterns
(if any). If a log message matches any of the denied patterns, it will be discarded,
whatever the allowed patterns. Then, remaining log messages are tested against allowed
patterns. Messages matching against none of the allowed pattern are discarded. If no
allowed patterns are defined, then all messages are processed directly after going
through denied filters.

Filtering is based on the unit for which LogFilterPatterns= is defined, meaning log
messages coming from systemd(1) about the unit are not taken into account. Filtered log
messages won't be forwarded to traditional syslog daemons, the kernel log buffer (kmsg),
the systemd console, or sent as wall messages to all logged-in users.

Added in version 253.

LogNamespace=
Run the unit's processes in the specified journal namespace. Expects a short user-defined
string identifying the namespace. If not used the processes of the service are run in the
default journal namespace, i.e. their log stream is collected and processed by
systemd-journald.service. If this option is used any log data generated by processes of
this unit (regardless if via the syslog(), journal native logging or stdout/stderr
logging) is collected and processed by an instance of the systemd-journald@.service
template unit, which manages the specified namespace. The log data is stored in a data
store independent from the default log namespace's data store. See systemd-
journald.service(8) for details about journal namespaces.

Internally, journal namespaces are implemented through Linux mount namespacing and
over-mounting the directory that contains the relevant AF_UNIX sockets used for logging
in the unit's mount namespace. Since mount namespaces are used this setting disconnects
propagation of mounts from the unit's processes to the host, similarly to how
ReadOnlyPaths= and similar settings describe above work. Journal namespaces may hence not
be used for services that need to establish mount points on the host.

When this option is used the unit will automatically gain ordering and requirement
dependencies on the two socket units associated with the systemd-journald@.service
instance so that they are automatically established prior to the unit starting up. Note
that when this option is used log output of this service does not appear in the regular
journalctl(1) output, unless the --namespace= option is used.

This option is only available for system services and is not supported for services
running in per-user instances of the service manager.

Added in version 245.

SyslogIdentifier=
Sets the process name ("syslog tag") to prefix log lines sent to the logging system or
the kernel log buffer with. If not set, defaults to the process name of the executed
process. This option is only useful when StandardOutput= or StandardError= are set to
journal or kmsg (or to the same settings in combination with +console) and only applies
to log messages written to stdout or stderr.

SyslogFacility=
Sets the syslog facility identifier to use when logging. One of kern, user, mail, daemon,
auth, syslog, lpr, news, uucp, cron, authpriv, ftp, local0, local1, local2, local3,
local4, local5, local6 or local7. See syslog(3) for details. This option is only useful
when StandardOutput= or StandardError= are set to journal or kmsg (or to the same
settings in combination with +console), and only applies to log messages written to
stdout or stderr. Defaults to daemon.

SyslogLevel=
The default syslog log level to use when logging to the logging system or the kernel log
buffer. One of emerg, alert, crit, err, warning, notice, info, debug. See syslog(3) for
details. This option is only useful when StandardOutput= or StandardError= are set to
journal or kmsg (or to the same settings in combination with +console), and only applies
to log messages written to stdout or stderr. Note that individual lines output by
executed processes may be prefixed with a different log level which can be used to
override the default log level specified here. The interpretation of these prefixes may
be disabled with SyslogLevelPrefix=, see below. For details, see sd-daemon(3). Defaults
to info.

SyslogLevelPrefix=
Takes a boolean argument. If true and StandardOutput= or StandardError= are set to
journal or kmsg (or to the same settings in combination with +console), log lines written
by the executed process that are prefixed with a log level will be processed with this
log level set but the prefix removed. If set to false, the interpretation of these
prefixes is disabled and the logged lines are passed on as-is. This only applies to log
messages written to stdout or stderr. For details about this prefixing see sd-daemon(3).
Defaults to true.

TTYPath=
Sets the terminal device node to use if standard input, output, or error are connected to
a TTY (see above). Defaults to /dev/console.

TTYReset=
Reset the terminal device specified with TTYPath= before and after execution. Defaults to
"no".

TTYVHangup=
Disconnect all clients which have opened the terminal device specified with TTYPath=
before and after execution. Defaults to "no".

TTYRows=, TTYColumns=
Configure the size of the TTY specified with TTYPath=. If unset or set to the empty
string, the kernel default is used.

Added in version 250.

TTYVTDisallocate=
If the terminal device specified with TTYPath= is a virtual console terminal, try to
deallocate the TTY before and after execution. This ensures that the screen and
scrollback buffer is cleared. Defaults to "no".

CREDENTIALS
LoadCredential=ID[:PATH], LoadCredentialEncrypted=ID[:PATH]
Pass a credential to the unit. Credentials are limited-size binary or textual objects
that may be passed to unit processes. They are primarily used for passing cryptographic
keys (both public and private) or certificates, user account information or identity
information from host to services. The data is accessible from the unit's processes via
the file system, at a read-only location that (if possible and permitted) is backed by
non-swappable memory. The data is only accessible to the user associated with the unit,
via the User=/DynamicUser= settings (as well as the superuser). When available, the
location of credentials is exported as the $CREDENTIALS_DIRECTORY environment variable to
the unit's processes.

The LoadCredential= setting takes a textual ID to use as name for a credential plus a
file system path, separated by a colon. The ID must be a short ASCII string suitable as
filename in the filesystem, and may be chosen freely by the user. If the specified path
is absolute it is opened as regular file and the credential data is read from it. If the
absolute path refers to an AF_UNIX stream socket in the file system a connection is made
to it (only once at unit start-up) and the credential data read from the connection,
providing an easy IPC integration point for dynamically transferring credentials from
other services.

If the specified path is not absolute and itself qualifies as valid credential identifier
it is attempted to find a credential that the service manager itself received under the
specified name — which may be used to propagate credentials from an invoking environment
(e.g. a container manager that invoked the service manager) into a service. If no
matching system credential is found, the directories /etc/credstore/, /run/credstore/ and
/usr/lib/credstore/ are searched for files under the credential's name — which hence are
recommended locations for credential data on disk. If LoadCredentialEncrypted= is used
/run/credstore.encrypted/, /etc/credstore.encrypted/, and /usr/lib/credstore.encrypted/
are searched as well.

If the file system path is omitted it is chosen identical to the credential name, i.e.
this is a terse way to declare credentials to inherit from the service manager into a
service. This option may be used multiple times, each time defining an additional
credential to pass to the unit.

If an absolute path referring to a directory is specified, every file in that directory
(recursively) will be loaded as a separate credential. The ID for each credential will be
the provided ID suffixed with "_$FILENAME" (e.g., "Key_file1"). When loading from a
directory, symlinks will be ignored.

The contents of the file/socket may be arbitrary binary or textual data, including
newline characters and NUL bytes.

The LoadCredentialEncrypted= setting is identical to LoadCredential=, except that the
credential data is decrypted and authenticated before being passed on to the executed
processes. Specifically, the referenced path should refer to a file or socket with an
encrypted credential, as implemented by systemd-creds(1). This credential is loaded,
decrypted, authenticated and then passed to the application in plaintext form, in the
same way a regular credential specified via LoadCredential= would be. A credential
configured this way may be symmetrically encrypted/authenticated with a secret key
derived from the system's TPM2 security chip, or with a secret key stored in
/var/lib/systemd/credentials.secret, or with both. Using encrypted and authenticated
credentials improves security as credentials are not stored in plaintext and only
authenticated and decrypted into plaintext the moment a service requiring them is
started. Moreover, credentials may be bound to the local hardware and installations, so
that they cannot easily be analyzed offline, or be generated externally. When
DevicePolicy= is set to "closed" or "strict", or set to "auto" and DeviceAllow= is set,
or PrivateDevices= is set, then this setting adds /dev/tpmrm0 with rw mode to
DeviceAllow=. See systemd.resource-control(5) for the details about DevicePolicy= or
DeviceAllow=.

The credential files/IPC sockets must be accessible to the service manager, but don't
have to be directly accessible to the unit's processes: the credential data is read and
copied into separate, read-only copies for the unit that are accessible to appropriately
privileged processes. This is particularly useful in combination with DynamicUser= as
this way privileged data can be made available to processes running under a dynamic UID
(i.e. not a previously known one) without having to open up access to all users.

In order to reference the path a credential may be read from within a ExecStart= command
line use "${CREDENTIALS_DIRECTORY}/mycred", e.g. "ExecStart=cat
${CREDENTIALS_DIRECTORY}/mycred". In order to reference the path a credential may be read
from within a Environment= line use "%d/mycred", e.g.
"Environment=MYCREDPATH=%d/mycred". For system services the path may also be referenced
as "/run/credentials/UNITNAME" in cases where no interpolation is possible, e.g.
configuration files of software that does not yet support credentials natively.
$CREDENTIALS_DIRECTORY is considered the primary interface to look for credentials,
though, since it also works for user services.

Currently, an accumulated credential size limit of 1 MB per unit is enforced.

The service manager itself may receive system credentials that can be propagated to
services from a hosting container manager or VM hypervisor. See the Container
Interface[15] documentation for details about the former. For the latter, pass
DMI/SMBIOS[16] OEM string table entries (field type 11) with a prefix of
"io.systemd.credential:" or "io.systemd.credential.binary:". In both cases a key/value
pair separated by "=" is expected, in the latter case the right-hand side is Base64
decoded when parsed (thus permitting binary data to be passed in). Example qemu[17]
switch: "-smbios type=11,value=io.systemd.credential:xx=yy", or "-smbios
type=11,value=io.systemd.credential.binary:rick=TmV2ZXIgR29ubmEgR2l2ZSBZb3UgVXA=".
Alternatively, use the qemu "fw_cfg" node "opt/io.systemd.credentials/". Example qemu
switch: "-fw_cfg name=opt/io.systemd.credentials/mycred,string=supersecret". They may
also be passed from the UEFI firmware environment via systemd-stub(7), from the initrd
(see systemd(1)), or be specified on the kernel command line using the
"systemd.set_credential=" and "systemd.set_credential_binary=" switches (see systemd(1) –
this is not recommended since unprivileged userspace can read the kernel command line).

If referencing an AF_UNIX stream socket to connect to, the connection will originate from
an abstract namespace socket, that includes information about the unit and the credential
ID in its socket name. Use getpeername(2) to query this information. The returned socket
name is formatted as NUL RANDOM "/unit/" UNIT "/" ID, i.e. a NUL byte (as required for
abstract namespace socket names), followed by a random string (consisting of alphadecimal
characters), followed by the literal string "/unit/", followed by the requesting unit
name, followed by the literal character "/", followed by the textual credential ID
requested. Example: "\0adf9d86b6eda275e/unit/foobar.service/credx" in case the credential
"credx" is requested for a unit "foobar.service". This functionality is useful for using
a single listening socket to serve credentials to multiple consumers.

For further information see System and Service Credentials[18] documentation.

Added in version 247.

ImportCredential=GLOB
Pass one or more credentials to the unit. Takes a credential name for which we'll attempt
to find a credential that the service manager itself received under the specified name —
which may be used to propagate credentials from an invoking environment (e.g. a container
manager that invoked the service manager) into a service. If the credential name is a
glob, all credentials matching the glob are passed to the unit. Matching credentials are
searched for in the system credentials, the encrypted system credentials, and under
/etc/credstore/, /run/credstore/, /usr/lib/credstore/, /run/credstore.encrypted/,
/etc/credstore.encrypted/, and /usr/lib/credstore.encrypted/ in that order. When multiple
credentials of the same name are found, the first one found is used.

The globbing expression implements a restrictive subset of glob(7): only a single
trailing "*" wildcard may be specified. Both "?" and "[]" wildcards are not permitted,
nor are "*" wildcards anywhere except at the end of the glob expression.

When multiple credentials of the same name are found, credentials found by
LoadCredential= and LoadCredentialEncrypted= take priority over credentials found by
ImportCredential=.

Added in version 254.

SetCredential=ID:VALUE, SetCredentialEncrypted=ID:VALUE
The SetCredential= setting is similar to LoadCredential= but accepts a literal value to
use as data for the credential, instead of a file system path to read the data from. Do
not use this option for data that is supposed to be secret, as it is accessible to
unprivileged processes via IPC. It's only safe to use this for user IDs, public key
material and similar non-sensitive data. For everything else use LoadCredential=. In
order to embed binary data into the credential data use C-style escaping (i.e. "\n" to
embed a newline, or "\x00" to embed a NUL byte).

The SetCredentialEncrypted= setting is identical to SetCredential= but expects an
encrypted credential in literal form as value. This allows embedding confidential
credentials securely directly in unit files. Use systemd-creds(1)' -p switch to generate
suitable SetCredentialEncrypted= lines directly from plaintext credentials. For further
details see LoadCredentialEncrypted= above.

When multiple credentials of the same name are found, credentials found by
LoadCredential=, LoadCredentialEncrypted= and ImportCredential= take priority over
credentials found by SetCredential=. As such, SetCredential= will act as default if no
credentials are found by any of the former. In this case not being able to retrieve the
credential from the path specified in LoadCredential= or LoadCredentialEncrypted= is not
considered fatal.

Added in version 247.

SYSTEM V COMPATIBILITY
UtmpIdentifier=
Takes a four character identifier string for an utmp(5) and wtmp entry for this service.
This should only be set for services such as getty implementations (such as agetty(8))
where utmp/wtmp entries must be created and cleared before and after execution, or for
services that shall be executed as if they were run by a getty process (see below). If
the configured string is longer than four characters, it is truncated and the terminal
four characters are used. This setting interprets %I style string replacements. This
setting is unset by default, i.e. no utmp/wtmp entries are created or cleaned up for this
service.

UtmpMode=
Takes one of "init", "login" or "user". If UtmpIdentifier= is set, controls which type of
utmp(5)/wtmp entries for this service are generated. This setting has no effect unless
UtmpIdentifier= is set too. If "init" is set, only an INIT_PROCESS entry is generated and
the invoked process must implement a getty-compatible utmp/wtmp logic. If "login" is set,
first an INIT_PROCESS entry, followed by a LOGIN_PROCESS entry is generated. In this
case, the invoked process must implement a login(1)-compatible utmp/wtmp logic. If "user"
is set, first an INIT_PROCESS entry, then a LOGIN_PROCESS entry and finally a
USER_PROCESS entry is generated. In this case, the invoked process may be any process
that is suitable to be run as session leader. Defaults to "init".

Added in version 225.

ENVIRONMENT VARIABLES IN SPAWNED PROCESSES
Processes started by the service manager are executed with an environment variable block
assembled from multiple sources. Processes started by the system service manager generally do
not inherit environment variables set for the service manager itself (but this may be altered
via PassEnvironment=), but processes started by the user service manager instances generally
do inherit all environment variables set for the service manager itself.

For each invoked process the list of environment variables set is compiled from the following
sources:

• Variables globally configured for the service manager, using the DefaultEnvironment=
setting in systemd-system.conf(5), the kernel command line option systemd.setenv=
understood by systemd(1), or via systemctl(1) set-environment verb.

• Variables defined by the service manager itself (see the list below).

• Variables set in the service manager's own environment variable block (subject to
PassEnvironment= for the system service manager).

• Variables set via Environment= in the unit file.

• Variables read from files specified via EnvironmentFile= in the unit file.

• Variables set by any PAM modules in case PAMName= is in effect, cf. pam_env(8).

If the same environment variable is set by multiple of these sources, the later source —
according to the order of the list above — wins. Note that as the final step all variables
listed in UnsetEnvironment= are removed from the compiled environment variable list,
immediately before it is passed to the executed process.

The general philosophy is to expose a small curated list of environment variables to
processes. Services started by the system manager (PID 1) will be started, without additional
service-specific configuration, with just a few environment variables. The user manager
inherits environment variables as any other system service, but in addition may receive
additional environment variables from PAM, and, typically, additional imported variables when
the user starts a graphical session. It is recommended to keep the environment blocks in both
the system and user managers lean. Importing all variables inherited by the graphical session
or by one of the user shells is strongly discouraged.

Hint: systemd-run -P env and systemd-run --user -P env print the effective system and user
service environment blocks.

Environment Variables Set or Propagated by the Service Manager
The following environment variables are propagated by the service manager or generated
internally for each invoked process:

$PATH
Colon-separated list of directories to use when launching executables. systemd uses a
fixed value of "/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin" in the system manager.
In case of the user manager, a different path may be configured by the distribution. It
is recommended to not rely on the order of entries, and have only one program with a
given name in $PATH.

Added in version 208.

$LANG
Locale. Can be set in locale.conf(5) or on the kernel command line (see systemd(1) and
kernel-command-line(7)).

Added in version 208.

$USER, $LOGNAME, $HOME, $SHELL
User name (twice), home directory, and the login shell. $USER is set unconditionally,
while $HOME, $LOGNAME, and $SHELL are only set for the units that have User= set and
SetLoginEnvironment= unset or set to true. For user services, these variables are
typically inherited from the user manager itself. See passwd(5).

Added in version 208.

$INVOCATION_ID
Contains a randomized, unique 128-bit ID identifying each runtime cycle of the unit,
formatted as 32 character hexadecimal string. A new ID is assigned each time the unit
changes from an inactive state into an activating or active state, and may be used to
identify this specific runtime cycle, in particular in data stored offline, such as the
journal. The same ID is passed to all processes run as part of the unit.

Added in version 232.

$XDG_RUNTIME_DIR
The directory to use for runtime objects (such as IPC objects) and volatile state. Set
for all services run by the user systemd instance, as well as any system services that
use PAMName= with a PAM stack that includes pam_systemd. See below and pam_systemd(8) for
more information.

Added in version 208.

$RUNTIME_DIRECTORY, $STATE_DIRECTORY, $CACHE_DIRECTORY, $LOGS_DIRECTORY,
$CONFIGURATION_DIRECTORY
Absolute paths to the directories defined with RuntimeDirectory=, StateDirectory=,
CacheDirectory=, LogsDirectory=, and ConfigurationDirectory= when those settings are
used.

Added in version 244.

$CREDENTIALS_DIRECTORY
An absolute path to the per-unit directory with credentials configured via
ImportCredential=/LoadCredential=/SetCredential=. The directory is marked read-only and
is placed in unswappable memory (if supported and permitted), and is only accessible to
the UID associated with the unit via User= or DynamicUser= (and the superuser).

Added in version 247.

$MAINPID
The PID of the unit's main process if it is known. This is only set for control processes
as invoked by ExecReload= and similar.

Added in version 209.

$MANAGERPID
The PID of the user systemd instance, set for processes spawned by it.

Added in version 208.

$LISTEN_FDS, $LISTEN_PID, $LISTEN_FDNAMES
Information about file descriptors passed to a service for socket activation. See
sd_listen_fds(3).

Added in version 208.

$NOTIFY_SOCKET
The socket sd_notify() talks to. See sd_notify(3).

Added in version 229.

$WATCHDOG_PID, $WATCHDOG_USEC
Information about watchdog keep-alive notifications. See sd_watchdog_enabled(3).

Added in version 229.

$SYSTEMD_EXEC_PID
The PID of the unit process (e.g. process invoked by ExecStart=). The child process can
use this information to determine whether the process is directly invoked by the service
manager or indirectly as a child of another process by comparing this value with the
current PID (similarly to the scheme used in sd_listen_fds(3) with $LISTEN_PID and
$LISTEN_FDS).

Added in version 248.

$TERM
Terminal type, set only for units connected to a terminal (StandardInput=tty,
StandardOutput=tty, or StandardError=tty). See termcap(5).

Added in version 209.

$LOG_NAMESPACE
Contains the name of the selected logging namespace when the LogNamespace= service
setting is used.

Added in version 246.

$JOURNAL_STREAM
If the standard output or standard error output of the executed processes are connected
to the journal (for example, by setting StandardError=journal) $JOURNAL_STREAM contains
the device and inode numbers of the connection file descriptor, formatted in decimal,
separated by a colon (":"). This permits invoked processes to safely detect whether their
standard output or standard error output are connected to the journal. The device and
inode numbers of the file descriptors should be compared with the values set in the
environment variable to determine whether the process output is still connected to the
journal. Note that it is generally not sufficient to only check whether $JOURNAL_STREAM
is set at all as services might invoke external processes replacing their standard output
or standard error output, without unsetting the environment variable.

If both standard output and standard error of the executed processes are connected to the
journal via a stream socket, this environment variable will contain information about the
standard error stream, as that's usually the preferred destination for log data. (Note
that typically the same stream is used for both standard output and standard error, hence
very likely the environment variable contains device and inode information matching both
stream file descriptors.)

This environment variable is primarily useful to allow services to optionally upgrade
their used log protocol to the native journal protocol (using sd_journal_print(3) and
other functions) if their standard output or standard error output is connected to the
journal anyway, thus enabling delivery of structured metadata along with logged messages.

Added in version 231.

$SERVICE_RESULT
Only used for the service unit type. This environment variable is passed to all ExecStop=
and ExecStopPost= processes, and encodes the service "result". Currently, the following
values are defined:

Table 5. Defined $SERVICE_RESULT values
┌───────────────────┬───────────────────────────────────┐
│ Value │ Meaning │
├───────────────────┼───────────────────────────────────┤
│ "success" │ The service ran successfully and │
│ │ exited cleanly. │
├───────────────────┼───────────────────────────────────┤
│ "protocol" │ A protocol violation occurred: │
│ │ the service did not take the │
│ │ steps required by its unit │
│ │ configuration (specifically what │
│ │ is configured in its Type= │
│ │ setting). │
├───────────────────┼───────────────────────────────────┤
│ "timeout" │ One of the steps timed out. │
├───────────────────┼───────────────────────────────────┤
│ "exit-code" │ Service process exited with a │
│ │ non-zero exit code; see │
│ │ $EXIT_CODE below for the actual │
│ │ exit code returned. │
├───────────────────┼───────────────────────────────────┤
│ "signal" │ A service process was terminated │
│ │ abnormally by a signal, without │
│ │ dumping core. See $EXIT_CODE │
│ │ below for the actual signal │
│ │ causing the termination. │
├───────────────────┼───────────────────────────────────┤
│ "core-dump" │ A service process terminated │
│ │ abnormally with a signal and │
│ │ dumped core. See $EXIT_CODE below │
│ │ for the signal causing the │
│ │ termination. │
├───────────────────┼───────────────────────────────────┤
│ "watchdog" │ Watchdog keep-alive ping was │
│ │ enabled for the service, but the │
│ │ deadline was missed. │
├───────────────────┼───────────────────────────────────┤
│ "exec-condition" │ Service did not run because │
│ │ ExecCondition= failed. │
├───────────────────┼───────────────────────────────────┤
│ "oom-kill" │ A service process was terminated │
│ │ by the Out-Of-Memory (OOM) │
│ │ killer. │
├───────────────────┼───────────────────────────────────┤
│ "start-limit-hit" │ A start limit was defined for the │
│ │ unit and it was hit, causing the │
│ │ unit to fail to start. See │
│ │ systemd.unit(5)'s │
│ │ StartLimitIntervalSec= and │
│ │ StartLimitBurst= for details. │
├───────────────────┼───────────────────────────────────┤
│ "resources" │ A catch-all condition in case a │
│ │ system operation failed. │
└───────────────────┴───────────────────────────────────┘

This environment variable is useful to monitor failure or successful termination of a
service. Even though this variable is available in both ExecStop= and ExecStopPost=, it
is usually a better choice to place monitoring tools in the latter, as the former is only
invoked for services that managed to start up correctly, and the latter covers both
services that failed during their start-up and those which failed during their runtime.

Added in version 232.

$EXIT_CODE, $EXIT_STATUS
Only defined for the service unit type. These environment variables are passed to all
ExecStop=, ExecStopPost= processes and contain exit status/code information of the main
process of the service. For the precise definition of the exit code and status, see
wait(2). $EXIT_CODE is one of "exited", "killed", "dumped". $EXIT_STATUS contains the
numeric exit code formatted as string if $EXIT_CODE is "exited", and the signal name in
all other cases. Note that these environment variables are only set if the service
manager succeeded to start and identify the main process of the service.

Table 6. Summary of possible service result variable values
┌───────────────────────┬──────────────────────┬──────────────────────────────┐
│ $SERVICE_RESULT │ $EXIT_CODE │$EXIT_STATUS │
├───────────────────────┼──────────────────────┼──────────────────────────────┤
│ "success" │ "killed" │"HUP", "INT", "TERM", │
│ │ │"PIPE" │
│ ├──────────────────────┼──────────────────────────────┤
│ │ "exited" │"0" │
├───────────────────────┼──────────────────────┼──────────────────────────────┤
│ "protocol" │ not set │not set │
│ ├──────────────────────┼──────────────────────────────┤
│ │ "exited" │"0" │
├───────────────────────┼──────────────────────┼──────────────────────────────┤
│ "timeout" │ "killed" │"TERM", "KILL" │
│ ├──────────────────────┼──────────────────────────────┤
│ │ "exited" │"0", "1", "2", "3", ..., │
│ │ │"255" │
├───────────────────────┼──────────────────────┼──────────────────────────────┤
│ "exit-code" │ "exited" │"1", "2", "3", ..., "255" │
├───────────────────────┼──────────────────────┼──────────────────────────────┤
│ "signal" │ "killed" │"HUP", "INT", "KILL", ... │
├───────────────────────┼──────────────────────┼──────────────────────────────┤
│ "core-dump" │ "dumped" │"ABRT", "SEGV", "QUIT", │
│ │ │... │
├───────────────────────┼──────────────────────┼──────────────────────────────┤
│ "watchdog" │ "dumped" │"ABRT" │
│ ├──────────────────────┼──────────────────────────────┤
│ │ "killed" │"TERM", "KILL" │
│ ├──────────────────────┼──────────────────────────────┤
│ │ "exited" │"0", "1", "2", "3", ..., │
│ │ │"255" │
├───────────────────────┼──────────────────────┼──────────────────────────────┤
│ "exec-condition" │ "exited" │"1", "2", "3", "4", ..., │
│ │ │"254" │
├───────────────────────┼──────────────────────┼──────────────────────────────┤
│ "oom-kill" │ "killed" │"TERM", "KILL" │
├───────────────────────┼──────────────────────┼──────────────────────────────┤
│ "start-limit-hit" │ not set │not set │
├───────────────────────┼──────────────────────┼──────────────────────────────┤
│ "resources" │ any of the above │any of the above │
├───────────────────────┴──────────────────────┴──────────────────────────────┤
│ Note: the process may be also terminated by a signal not sent by systemd. │
│ In particular the process may send an arbitrary signal to itself in a │
│ handler for any of the non-maskable signals. Nevertheless, in the "timeout" │
│ and "watchdog" rows above only the signals that systemd sends have been │
│ included. Moreover, using SuccessExitStatus= additional exit statuses may │
│ be declared to indicate clean termination, which is not reflected by this │
│ table. │
└─────────────────────────────────────────────────────────────────────────────┘

Added in version 232.

$MONITOR_SERVICE_RESULT, $MONITOR_EXIT_CODE, $MONITOR_EXIT_STATUS, $MONITOR_INVOCATION_ID,
$MONITOR_UNIT
Only defined for the service unit type. Those environment variables are passed to all
ExecStart= and ExecStartPre= processes which run in services triggered by OnFailure= or
OnSuccess= dependencies.

Variables $MONITOR_SERVICE_RESULT, $MONITOR_EXIT_CODE and $MONITOR_EXIT_STATUS take the
same values as for ExecStop= and ExecStopPost= processes. Variables
$MONITOR_INVOCATION_ID and $MONITOR_UNIT are set to the invocation id and unit name of
the service which triggered the dependency.

Note that when multiple services trigger the same unit, those variables will be not be
passed. Consider using a template handler unit for that case instead:
"OnFailure=handler@%n.service" for non-templated units, or
"OnFailure=handler@%p-%i.service" for templated units.

Added in version 251.

$PIDFILE
The path to the configured PID file, in case the process is forked off on behalf of a
service that uses the PIDFile= setting, see systemd.service(5) for details. Service code
may use this environment variable to automatically generate a PID file at the location
configured in the unit file. This field is set to an absolute path in the file system.

Added in version 242.

$REMOTE_ADDR, $REMOTE_PORT
If this is a unit started via per-connection socket activation (i.e. via a socket unit
with Accept=yes), these environment variables contain the IP address and port number of
the remote peer of the socket connection.

Added in version 254.

$TRIGGER_UNIT, $TRIGGER_PATH, $TRIGGER_TIMER_REALTIME_USEC, $TRIGGER_TIMER_MONOTONIC_USEC
If the unit was activated dynamically (e.g.: a corresponding path unit or timer unit),
the unit that triggered it and other type-dependent information will be passed via these
variables. Note that this information is provided in a best-effort way. For example,
multiple triggers happening one after another will be coalesced and only one will be
reported, with no guarantee as to which one it will be. Because of this, in most cases
this variable will be primarily informational, i.e. useful for debugging purposes, is
lossy, and should not be relied upon to propagate a comprehensive reason for activation.

Added in version 252.

$MEMORY_PRESSURE_WATCH, $MEMORY_PRESSURE_WRITE
If memory pressure monitoring is enabled for this service unit, the path to watch and the
data to write into it. See Memory Pressure Handling[19] for details about these variables
and the service protocol data they convey.

Added in version 254.

$FDSTORE
The maximum number of file descriptors that may be stored in the manager for the service.
This variable is set when the file descriptor store is enabled for the service, i.e.
FileDescriptorStoreMax= is set to a non-zero value (see systemd.service(5) for details).
Applications may check this environment variable before sending file descriptors to the
service manager via sd_pid_notify_with_fds(3).

Added in version 254.

For system services, when PAMName= is enabled and pam_systemd is part of the selected PAM
stack, additional environment variables defined by systemd may be set for services.
Specifically, these are $XDG_SEAT, $XDG_VTNR, see pam_systemd(8) for details.

PROCESS EXIT CODES
When invoking a unit process the service manager possibly fails to apply the execution
parameters configured with the settings above. In that case the already created service
process will exit with a non-zero exit code before the configured command line is executed.
(Or in other words, the child process possibly exits with these error codes, after having
been created by the fork(2) system call, but before the matching execve(2) system call is
called.) Specifically, exit codes defined by the C library, by the LSB specification and by
the systemd service manager itself are used.

The following basic service exit codes are defined by the C library.

Table 7. Basic C library exit codes
┌───────────┬───────────────┬───────────────────────┐
│ Exit Code │ Symbolic Name │ Description │
├───────────┼───────────────┼───────────────────────┤
│ 0 │ EXIT_SUCCESS │ Generic success code. │
├───────────┼───────────────┼───────────────────────┤
│ 1 │ EXIT_FAILURE │ Generic failure or │
│ │ │ unspecified error. │
└───────────┴───────────────┴───────────────────────┘

The following service exit codes are defined by the LSB specification[20].

Table 8. LSB service exit codes
┌───────────┬──────────────────────┬───────────────────────────┐
│ Exit Code │ Symbolic Name │ Description │
├───────────┼──────────────────────┼───────────────────────────┤
│ 2 │ EXIT_INVALIDARGUMENT │ Invalid or excess │
│ │ │ arguments. │
├───────────┼──────────────────────┼───────────────────────────┤
│ 3 │ EXIT_NOTIMPLEMENTED │ Unimplemented feature. │
├───────────┼──────────────────────┼───────────────────────────┤
│ 4 │ EXIT_NOPERMISSION │ The user has insufficient │
│ │ │ privileges. │
├───────────┼──────────────────────┼───────────────────────────┤
│ 5 │ EXIT_NOTINSTALLED │ The program is not │
│ │ │ installed. │
├───────────┼──────────────────────┼───────────────────────────┤
│ 6 │ EXIT_NOTCONFIGURED │ The program is not │
│ │ │ configured. │
├───────────┼──────────────────────┼───────────────────────────┤
│ 7 │ EXIT_NOTRUNNING │ The program is not │
│ │ │ running. │
└───────────┴──────────────────────┴───────────────────────────┘

The LSB specification suggests that error codes 200 and above are reserved for
implementations. Some of them are used by the service manager to indicate problems during
process invocation:

Table 9. systemd-specific exit codes
┌───────────┬──────────────────────────────┬─────────────────────────────────────────────┐
│ Exit Code │ Symbolic Name │ Description │
├───────────┼──────────────────────────────┼─────────────────────────────────────────────┤
│ 200 │ EXIT_CHDIR │ Changing to the requested │
│ │ │ working directory failed. │
│ │ │ See WorkingDirectory= │
│ │ │ above. │
├───────────┼──────────────────────────────┼─────────────────────────────────────────────┤
│ 201 │ EXIT_NICE │ Failed to set up process │
│ │ │ scheduling priority (nice │
│ │ │ level). See Nice= above. │
├───────────┼──────────────────────────────┼─────────────────────────────────────────────┤
│ 202 │ EXIT_FDS │ Failed to close unwanted │
│ │ │ file descriptors, or to │
│ │ │ adjust passed file │
│ │ │ descriptors. │
├───────────┼──────────────────────────────┼─────────────────────────────────────────────┤
│ 203 │ EXIT_EXEC │ The actual process │
│ │ │ execution failed │
│ │ │ (specifically, the │
│ │ │ execve(2) system call). │
│ │ │ Most likely this is │
│ │ │ caused by a missing or │
│ │ │ non-accessible executable │
│ │ │ file. │
├───────────┼──────────────────────────────┼─────────────────────────────────────────────┤
│ 204 │ EXIT_MEMORY │ Failed to perform an │
│ │ │ action due to memory │
│ │ │ shortage. │
├───────────┼──────────────────────────────┼─────────────────────────────────────────────┤
│ 205 │ EXIT_LIMITS │ Failed to adjust resource │
│ │ │ limits. See LimitCPU= and │
│ │ │ related settings above. │
├───────────┼──────────────────────────────┼─────────────────────────────────────────────┤
│ 206 │ EXIT_OOM_ADJUST │ Failed to adjust the OOM │
│ │ │ setting. See │
│ │ │ OOMScoreAdjust= above. │
├───────────┼──────────────────────────────┼─────────────────────────────────────────────┤
│ 207 │ EXIT_SIGNAL_MASK │ Failed to set process │
│ │ │ signal mask. │
├───────────┼──────────────────────────────┼─────────────────────────────────────────────┤
│ 208 │ EXIT_STDIN │ Failed to set up standard │
│ │ │ input. See StandardInput= │
│ │ │ above. │
├───────────┼──────────────────────────────┼─────────────────────────────────────────────┤
│ 209 │ EXIT_STDOUT │ Failed to set up standard │
│ │ │ output. See │
│ │ │ StandardOutput= above. │
├───────────┼──────────────────────────────┼─────────────────────────────────────────────┤
│ 210 │ EXIT_CHROOT │ Failed to change root │
│ │ │ directory (chroot(2)). │
│ │ │ See │
│ │ │ RootDirectory=/RootImage= │
│ │ │ above. │
├───────────┼──────────────────────────────┼─────────────────────────────────────────────┤
│ 211 │ EXIT_IOPRIO │ Failed to set up IO │
│ │ │ scheduling priority. See │
│ │ │ IOSchedulingClass=/IOSchedulingPriority= │
│ │ │ above. │
├───────────┼──────────────────────────────┼─────────────────────────────────────────────┤
│ 212 │ EXIT_TIMERSLACK │ Failed to set up timer slack. See │
│ │ │ TimerSlackNSec= above. │
├───────────┼──────────────────────────────┼─────────────────────────────────────────────┤
│ 213 │ EXIT_SECUREBITS │ Failed to set process secure bits. See │
│ │ │ SecureBits= above. │
├───────────┼──────────────────────────────┼─────────────────────────────────────────────┤
│ 214 │ EXIT_SETSCHEDULER │ Failed to set up CPU scheduling. See │
│ │ │ CPUSchedulingPolicy=/CPUSchedulingPriority= │
│ │ │ above. │
├───────────┼──────────────────────────────┼─────────────────────────────────────────────┤
│ 215 │ EXIT_CPUAFFINITY │ Failed to set up CPU affinity. See │
│ │ │ CPUAffinity= above. │
├───────────┼──────────────────────────────┼─────────────────────────────────────────────┤
│ 216 │ EXIT_GROUP │ Failed to determine or change group │
│ │ │ credentials. See │
│ │ │ Group=/SupplementaryGroups= above. │
├───────────┼──────────────────────────────┼─────────────────────────────────────────────┤
│ 217 │ EXIT_USER │ Failed to determine or change user │
│ │ │ credentials, or to set up user namespacing. │
│ │ │ See User=/PrivateUsers= above. │
├───────────┼──────────────────────────────┼─────────────────────────────────────────────┤
│ 218 │ EXIT_CAPABILITIES │ Failed to drop capabilities, or apply │
│ │ │ ambient capabilities. See │
│ │ │ CapabilityBoundingSet=/AmbientCapabilities= │
│ │ │ above. │
├───────────┼──────────────────────────────┼─────────────────────────────────────────────┤
│ 219 │ EXIT_CGROUP │ Setting up the service control group │
│ │ │ failed. │
├───────────┼──────────────────────────────┼─────────────────────────────────────────────┤
│ 220 │ EXIT_SETSID │ Failed to create new process session. │
├───────────┼──────────────────────────────┼─────────────────────────────────────────────┤
│ 221 │ EXIT_CONFIRM │ Execution has been cancelled by the user. │
│ │ │ See the systemd.confirm_spawn= kernel │
│ │ │ command line setting on kernel-command- │
│ │ │ line(7) for details. │
├───────────┼──────────────────────────────┼─────────────────────────────────────────────┤
│ 222 │ EXIT_STDERR │ Failed to set up standard error output. See │
│ │ │ StandardError= above. │
├───────────┼──────────────────────────────┼─────────────────────────────────────────────┤
│ 224 │ EXIT_PAM │ Failed to set up PAM session. See PAMName= │
│ │ │ above. │
├───────────┼──────────────────────────────┼─────────────────────────────────────────────┤
│ 225 │ EXIT_NETWORK │ Failed to set up network namespacing. See │
│ │ │ PrivateNetwork= above. │
├───────────┼──────────────────────────────┼─────────────────────────────────────────────┤
│ 226 │ EXIT_NAMESPACE │ Failed to set up mount, UTS, or IPC │
│ │ │ namespacing. See ReadOnlyPaths=, │
│ │ │ ProtectHostname=, PrivateIPC=, and related │
│ │ │ settings above. │
├───────────┼──────────────────────────────┼─────────────────────────────────────────────┤
│ 227 │ EXIT_NO_NEW_PRIVILEGES │ Failed to disable new privileges. See │
│ │ │ NoNewPrivileges=yes above. │
├───────────┼──────────────────────────────┼─────────────────────────────────────────────┤
│ 228 │ EXIT_SECCOMP │ Failed to apply system call filters. See │
│ │ │ SystemCallFilter= and related settings │
│ │ │ above. │
├───────────┼──────────────────────────────┼─────────────────────────────────────────────┤
│ 229 │ EXIT_SELINUX_CONTEXT │ Determining or changing SELinux context │
│ │ │ failed. See SELinuxContext= above. │
├───────────┼──────────────────────────────┼─────────────────────────────────────────────┤
│ 230 │ EXIT_PERSONALITY │ Failed to set up an execution domain │
│ │ │ (personality). See Personality= above. │
├───────────┼──────────────────────────────┼─────────────────────────────────────────────┤
│ 231 │ EXIT_APPARMOR_PROFILE │ Failed to prepare changing AppArmor │
│ │ │ profile. See AppArmorProfile= above. │
├───────────┼──────────────────────────────┼─────────────────────────────────────────────┤
│ 232 │ EXIT_ADDRESS_FAMILIES │ Failed to restrict address families. See │
│ │ │ RestrictAddressFamilies= above. │
├───────────┼──────────────────────────────┼─────────────────────────────────────────────┤
│ 233 │ EXIT_RUNTIME_DIRECTORY │ Setting up runtime directory failed. See │
│ │ │ RuntimeDirectory= and related settings │
│ │ │ above. │
├───────────┼──────────────────────────────┼─────────────────────────────────────────────┤
│ 235 │ EXIT_CHOWN │ Failed to adjust socket ownership. Used for │
│ │ │ socket units only. │
├───────────┼──────────────────────────────┼─────────────────────────────────────────────┤
│ 236 │ EXIT_SMACK_PROCESS_LABEL │ Failed to set SMACK label. See │
│ │ │ SmackProcessLabel= above. │
├───────────┼──────────────────────────────┼─────────────────────────────────────────────┤
│ 237 │ EXIT_KEYRING │ Failed to set up kernel keyring. │
├───────────┼──────────────────────────────┼─────────────────────────────────────────────┤
│ 238 │ EXIT_STATE_DIRECTORY │ Failed to set up unit's state directory. │
│ │ │ See StateDirectory= above. │
├───────────┼──────────────────────────────┼─────────────────────────────────────────────┤
│ 239 │ EXIT_CACHE_DIRECTORY │ Failed to set up unit's cache directory. │
│ │ │ See CacheDirectory= above. │
├───────────┼──────────────────────────────┼─────────────────────────────────────────────┤
│ 240 │ EXIT_LOGS_DIRECTORY │ Failed to set up unit's logging directory. │
│ │ │ See LogsDirectory= above. │
├───────────┼──────────────────────────────┼─────────────────────────────────────────────┤
│ 241 │ EXIT_CONFIGURATION_DIRECTORY │ Failed to set up unit's configuration │
│ │ │ directory. See ConfigurationDirectory= │
│ │ │ above. │
├───────────┼──────────────────────────────┼─────────────────────────────────────────────┤
│ 242 │ EXIT_NUMA_POLICY │ Failed to set up unit's NUMA memory policy. │
│ │ │ See NUMAPolicy= and NUMAMask= above. │
├───────────┼──────────────────────────────┼─────────────────────────────────────────────┤
│ 243 │ EXIT_CREDENTIALS │ Failed to set up unit's credentials. See │
│ │ │ ImportCredential=, LoadCredential= and │
│ │ │ SetCredential= above. │
├───────────┼──────────────────────────────┼─────────────────────────────────────────────┤
│ 245 │ EXIT_BPF │ Failed to apply BPF restrictions. See │
│ │ │ RestrictFileSystems= above. │
└───────────┴──────────────────────────────┴─────────────────────────────────────────────┘

Finally, the BSD operating systems define a set of exit codes, typically defined on Linux
systems too:

Table 10. BSD exit codes
┌───────────┬────────────────┬───────────────────────────┐
│ Exit Code │ Symbolic Name │ Description │
├───────────┼────────────────┼───────────────────────────┤
│ 64 │ EX_USAGE │ Command line usage error │
├───────────┼────────────────┼───────────────────────────┤
│ 65 │ EX_DATAERR │ Data format error │
├───────────┼────────────────┼───────────────────────────┤
│ 66 │ EX_NOINPUT │ Cannot open input │
├───────────┼────────────────┼───────────────────────────┤
│ 67 │ EX_NOUSER │ Addressee unknown │
├───────────┼────────────────┼───────────────────────────┤
│ 68 │ EX_NOHOST │ Host name unknown │
├───────────┼────────────────┼───────────────────────────┤
│ 69 │ EX_UNAVAILABLE │ Service unavailable │
├───────────┼────────────────┼───────────────────────────┤
│ 70 │ EX_SOFTWARE │ internal software error │
├───────────┼────────────────┼───────────────────────────┤
│ 71 │ EX_OSERR │ System error (e.g., can't │
│ │ │ fork) │
├───────────┼────────────────┼───────────────────────────┤
│ 72 │ EX_OSFILE │ Critical OS file missing │
├───────────┼────────────────┼───────────────────────────┤
│ 73 │ EX_CANTCREAT │ Can't create (user) │
│ │ │ output file │
├───────────┼────────────────┼───────────────────────────┤
│ 74 │ EX_IOERR │ Input/output error │
├───────────┼────────────────┼───────────────────────────┤
│ 75 │ EX_TEMPFAIL │ Temporary failure; user │
│ │ │ is invited to retry │
├───────────┼────────────────┼───────────────────────────┤
│ 76 │ EX_PROTOCOL │ Remote error in protocol │
├───────────┼────────────────┼───────────────────────────┤
│ 77 │ EX_NOPERM │ Permission denied │
├───────────┼────────────────┼───────────────────────────┤
│ 78 │ EX_CONFIG │ Configuration error │
└───────────┴────────────────┴───────────────────────────┘

EXAMPLES
Example 3. $MONITOR_* usage

A service myfailer.service which can trigger an OnFailure= dependency.

[Unit]
Description=Service which can trigger an OnFailure= dependency
OnFailure=myhandler.service

[Service]
ExecStart=/bin/myprogram

A service mysuccess.service which can trigger an OnSuccess= dependency.

[Unit]
Description=Service which can trigger an OnSuccess= dependency
OnSuccess=myhandler.service

[Service]
ExecStart=/bin/mysecondprogram

A service myhandler.service which can be triggered by any of the above services.

[Unit]
Description=Acts on service failing or succeeding

[Service]
ExecStart=/bin/bash -c "echo $MONITOR_SERVICE_RESULT $MONITOR_EXIT_CODE $MONITOR_EXIT_STATUS $MONITOR_INVOCATION_ID $MONITOR_UNIT"

If myfailer.service were to run and exit in failure, then myhandler.service would be
triggered and the monitor variables would be set as follows:

MONITOR_SERVICE_RESULT=exit-code
MONITOR_EXIT_CODE=exited
MONITOR_EXIT_STATUS=1
MONITOR_INVOCATION_ID=cc8fdc149b2b4ca698d4f259f4054236
MONITOR_UNIT=myfailer.service

If mysuccess.service were to run and exit in success, then myhandler.service would be
triggered and the monitor variables would be set as follows:

MONITOR_SERVICE_RESULT=success
MONITOR_EXIT_CODE=exited
MONITOR_EXIT_STATUS=0
MONITOR_INVOCATION_ID=6ab9af147b8c4a3ebe36e7a5f8611697
MONITOR_UNIT=mysuccess.service

SEE ALSO
systemd(1), systemctl(1), systemd-analyze(1), journalctl(1), systemd-system.conf(5),
systemd.unit(5), systemd.service(5), systemd.socket(5), systemd.swap(5), systemd.mount(5),
systemd.kill(5), systemd.resource-control(5), systemd.time(7), systemd.directives(7),
tmpfiles.d(5), exec(3), fork(2)

NOTES
1. Discoverable Partitions Specification
https://uapi-group.org/specifications/specs/discoverable_partitions_specification

2. The /proc Filesystem
https://docs.kernel.org/filesystems/proc.html#mount-options

3. User/Group Name Syntax
https://systemd.io/USER_NAMES

4. No New Privileges Flag
https://docs.kernel.org/userspace-api/no_new_privs.html

5. JSON User Record
https://systemd.io/USER_RECORD

6. The /proc Filesystem
https://docs.kernel.org/filesystems/proc.html

7. Kernel Samepage Merging
https://docs.kernel.org/admin-guide/mm/ksm.html

8. unicode scalar values
https://www.unicode.org/glossary/#unicode_scalar_value

9. unicode noncharacters
https://www.unicode.org/glossary/#noncharacter

10. unicode byte order mark
https://www.unicode.org/glossary/#byte_order_mark

11. POSIX shell unquoted text
https://pubs.opengroup.org/onlinepubs/9699919799/utilities/V3_chap02.html#tag_18_02_01

12. POSIX shell single-quoted text
https://pubs.opengroup.org/onlinepubs/9699919799/utilities/V3_chap02.html#tag_18_02_02

13. POSIX shell double-quoted text
https://pubs.opengroup.org/onlinepubs/9699919799/utilities/V3_chap02.html#tag_18_02_03

14. Base64
https://tools.ietf.org/html/rfc2045#section-6.8

15. Container Interface
https://systemd.io/CONTAINER_INTERFACE

16. DMI/SMBIOS
https://www.dmtf.org/standards/smbios

17. qemu
https://www.qemu.org/docs/master/system/index.html

18. System and Service Credentials
https://systemd.io/CREDENTIALS

19. Memory Pressure Handling
https://systemd.io/MEMORY_PRESSURE

20. LSB specification
https://refspecs.linuxbase.org/LSB_5.0.0/LSB-Core-generic/LSB-Core-generic/iniscrptact.html

systemd 255 SYSTEMD.EXEC(5)

Generated by phpman v4.11.2-59-gf06411a · Markdown · JSON Author: Che Dong Under GNU General Public License
2026-10-16 00:09 @216.73.216.218
CrawledBy Mozilla/5.0 AppleWebKit/537.36 (KHTML, like Gecko; compatible; ClaudeBot/1.0; +claudebot@anthropic.com)

man > systemd.exec(5)