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SYSTEMD-SYSTEM.CONF(5) systemd-system.conf SYSTEMD-SYSTEM.CONF(5)

NAME
systemd-system.conf, system.conf.d, systemd-user.conf, user.conf.d - System and session
service manager configuration files

SYNOPSIS
/etc/systemd/system.conf, /etc/systemd/system.conf.d/*.conf,
/run/systemd/system.conf.d/*.conf, /lib/systemd/system.conf.d/*.conf

~/.config/systemd/user.conf, /etc/systemd/user.conf, /etc/systemd/user.conf.d/*.conf,
/run/systemd/user.conf.d/*.conf, /usr/lib/systemd/user.conf.d/*.conf

DESCRIPTION
When run as a system instance, systemd interprets the configuration file system.conf and the
files in system.conf.d directories; when run as a user instance, it interprets the
configuration file user.conf (either in the home directory of the user, or if not found,
under /etc/systemd/) and the files in user.conf.d directories. These configuration files
contain a few settings controlling basic manager operations.

See systemd.syntax(7) for a general description of the syntax.

CONFIGURATION DIRECTORIES AND PRECEDENCE
The default configuration is set during compilation, so configuration is only needed when it
is necessary to deviate from those defaults. Initially, the main configuration file in
/etc/systemd/ contains commented out entries showing the defaults as a guide to the
administrator. Local overrides can be created by editing this file or by creating drop-ins,
as described below. Using drop-ins for local configuration is recommended over modifications
to the main configuration file.

In addition to the "main" configuration file, drop-in configuration snippets are read from
/usr/lib/systemd/*.conf.d/, /usr/local/lib/systemd/*.conf.d/, and /etc/systemd/*.conf.d/.
Those drop-ins have higher precedence and override the main configuration file. Files in the
*.conf.d/ configuration subdirectories are sorted by their filename in lexicographic order,
regardless of in which of the subdirectories they reside. When multiple files specify the
same option, for options which accept just a single value, the entry in the file sorted last
takes precedence, and for options which accept a list of values, entries are collected as
they occur in the sorted files.

When packages need to customize the configuration, they can install drop-ins under /usr/.
Files in /etc/ are reserved for the local administrator, who may use this logic to override
the configuration files installed by vendor packages. Drop-ins have to be used to override
package drop-ins, since the main configuration file has lower precedence. It is recommended
to prefix all filenames in those subdirectories with a two-digit number and a dash, to
simplify the ordering of the files.

To disable a configuration file supplied by the vendor, the recommended way is to place a
symlink to /dev/null in the configuration directory in /etc/, with the same filename as the
vendor configuration file.

OPTIONS
All options are configured in the [Manager] section:

LogColor=, LogLevel=, LogLocation=, LogTarget=, LogTime=, DumpCore=yes, CrashChangeVT=no,
CrashShell=no, CrashReboot=no, ShowStatus=yes, DefaultStandardOutput=journal,
DefaultStandardError=inherit
Configures various parameters of basic manager operation. These options may be overridden
by the respective process and kernel command line arguments. See systemd(1) for details.

CtrlAltDelBurstAction=
Defines what action will be performed if user presses Ctrl-Alt-Delete more than 7 times
in 2s. Can be set to "reboot-force", "poweroff-force", "reboot-immediate",
"poweroff-immediate" or disabled with "none". Defaults to "reboot-force".

CPUAffinity=
Configures the CPU affinity for the service manager as well as the default CPU affinity
for all forked off processes. Takes a list of CPU indices or ranges separated by either
whitespace or commas. 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. Individual services may
override the CPU affinity for their processes with the CPUAffinity= setting in unit
files, see systemd.exec(5).

NUMAPolicy=
Configures the NUMA memory policy for the service manager and the default NUMA memory
policy for all forked off processes. Individual services may override the default policy
with the NUMAPolicy= setting in unit files, see systemd.exec(5).

NUMAMask=
Configures the NUMA node mask that will be associated with the selected NUMA policy. Note
that default and local NUMA policies don't require explicit NUMA node mask and value of
the option can be empty. Similarly to NUMAPolicy=, value can be overridden by individual
services in unit files, see systemd.exec(5).

RuntimeWatchdogSec=, RebootWatchdogSec=, KExecWatchdogSec=
Configure the hardware watchdog at runtime and at reboot. Takes a timeout value in
seconds (or in other time units if suffixed with "ms", "min", "h", "d", "w"). If
RuntimeWatchdogSec= is set to a non-zero value, the watchdog hardware (/dev/watchdog or
the path specified with WatchdogDevice= or the kernel option systemd.watchdog-device=)
will be programmed to automatically reboot the system if it is not contacted within the
specified timeout interval. The system manager will ensure to contact it at least once in
half the specified timeout interval. This feature requires a hardware watchdog device to
be present, as it is commonly the case in embedded and server systems. Not all hardware
watchdogs allow configuration of all possible reboot timeout values, in which case the
closest available timeout is picked. RebootWatchdogSec= may be used to configure the
hardware watchdog when the system is asked to reboot. It works as a safety net to ensure
that the reboot takes place even if a clean reboot attempt times out. Note that the
RebootWatchdogSec= timeout applies only to the second phase of the reboot, i.e. after all
regular services are already terminated, and after the system and service manager process
(PID 1) got replaced by the systemd-shutdown binary, see system bootup(7) for details.
During the first phase of the shutdown operation the system and service manager remains
running and hence RuntimeWatchdogSec= is still honoured. In order to define a timeout on
this first phase of system shutdown, configure JobTimeoutSec= and JobTimeoutAction= in
the [Unit] section of the shutdown.target unit. By default RuntimeWatchdogSec= defaults
to 0 (off), and RebootWatchdogSec= to 10min. KExecWatchdogSec= may be used to
additionally enable the watchdog when kexec is being executed rather than when rebooting.
Note that if the kernel does not reset the watchdog on kexec (depending on the specific
hardware and/or driver), in this case the watchdog might not get disabled after kexec
succeeds and thus the system might get rebooted, unless RuntimeWatchdogSec= is also
enabled at the same time. For this reason it is recommended to enable KExecWatchdogSec=
only if RuntimeWatchdogSec= is also enabled. These settings have no effect if a hardware
watchdog is not available.

WatchdogDevice=
Configure the hardware watchdog device that the runtime and shutdown watchdog timers will
open and use. Defaults to /dev/watchdog. This setting has no effect if a hardware
watchdog is not available.

CapabilityBoundingSet=
Controls which capabilities to include in the capability bounding set for PID 1 and its
children. See capabilities(7) for details. Takes a whitespace-separated list of
capability names as read by cap_from_name(3). 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. The capability bounding set may also be individually
configured for units using the CapabilityBoundingSet= directive for units, but note that
capabilities dropped for PID 1 cannot be regained in individual units, they are lost for
good.

NoNewPrivileges=
Takes a boolean argument. If true, ensures that PID 1 and all its children can never gain
new privileges through execve(2) (e.g. via setuid or setgid bits, or filesystem
capabilities). Defaults to false. General purpose distributions commonly rely on
executables with setuid or setgid bits and will thus not function properly with this
option enabled. Individual units cannot disable this option. Also see No New Privileges
Flag[1].

SystemCallArchitectures=
Takes a space-separated list of architecture identifiers. Selects from which
architectures system calls may be invoked on this system. This may be used as an
effective way to disable invocation of non-native binaries system-wide, for example to
prohibit execution of 32-bit x86 binaries on 64-bit x86-64 systems. This option operates
system-wide, and acts similar to the SystemCallArchitectures= setting of unit files, see
systemd.exec(5) for details. This setting defaults to the empty list, in which case no
filtering of system calls based on architecture is applied. Known architecture
identifiers are "x86", "x86-64", "x32", "arm" and the special identifier "native". The
latter implicitly maps to the native architecture of the system (or more specifically,
the architecture the system manager was compiled for). Set this setting to "native" to
prohibit execution of any non-native binaries. When a binary executes a system call of an
architecture that is not listed in this setting, it will be immediately terminated with
the SIGSYS signal.

TimerSlackNSec=
Sets the timer slack in nanoseconds for PID 1, which is inherited by all executed
processes, unless overridden individually, for example with the TimerSlackNSec= setting
in service units (for details see systemd.exec(5)). The timer slack controls the accuracy
of wake-ups triggered by system 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.

StatusUnitFormat=
Takes name, description or combined as the value. If name, the system manager will use
unit names in status messages (e.g. "systemd-journald.service"), instead of the longer
and more informative descriptions set with Description= (e.g. "Journal Logging
Service"). If combined, the system manager will use both unit names and descriptions in
status messages (e.g. "systemd-journald.service - Journal Logging Service").

See systemd.unit(5) for details about unit names and Description=.

DefaultTimerAccuracySec=
Sets the default accuracy of timer units. This controls the global default for the
AccuracySec= setting of timer units, see systemd.timer(5) for details. AccuracySec= set
in individual units override the global default for the specific unit. Defaults to 1min.
Note that the accuracy of timer units is also affected by the configured timer slack for
PID 1, see TimerSlackNSec= above.

DefaultTimeoutStartSec=, DefaultTimeoutStopSec=, DefaultTimeoutAbortSec=, DefaultRestartSec=
Configures the default timeouts for starting, stopping and aborting of units, as well as
the default time to sleep between automatic restarts of units, as configured per-unit in
TimeoutStartSec=, TimeoutStopSec=, TimeoutAbortSec= and RestartSec= (for services, see
systemd.service(5) for details on the per-unit settings). Disabled by default, when
service with Type=oneshot is used. For non-service units, DefaultTimeoutStartSec= sets
the default TimeoutSec= value. DefaultTimeoutStartSec= and DefaultTimeoutStopSec=
default to 90s. DefaultTimeoutAbortSec= is not set by default so that all units fall
back to TimeoutStopSec=. DefaultRestartSec= defaults to 100ms.

DefaultStartLimitIntervalSec=, DefaultStartLimitBurst=
Configure the default unit start rate limiting, as configured per-service by
StartLimitIntervalSec= and StartLimitBurst=. See systemd.service(5) for details on the
per-service settings. DefaultStartLimitIntervalSec= defaults to 10s.
DefaultStartLimitBurst= defaults to 5.

DefaultEnvironment=
Configures environment variables passed to all executed processes. Takes a
space-separated list of variable assignments. See environ(7) for details about
environment variables.

Simple "%"-specifier expansion is supported, see below for a list of supported
specifiers.

Example:

DefaultEnvironment="VAR1=word1 word2" VAR2=word3 "VAR3=word 5 6"

Sets three variables "VAR1", "VAR2", "VAR3".

ManagerEnvironment=
Takes the same arguments as DefaultEnvironment=, see above. Sets environment variables
just for the manager process itself. In contrast to user managers, these variables are
not inherited by processes spawned by the system manager, use DefaultEnvironment= for
that. Note that these variables are merged into the existing environment block. In
particular, in case of the system manager, this includes variables set by the kernel
based on the kernel command line.

Setting environment variables for the manager process may be useful to modify its
behaviour. See ENVIRONMENT[2] for a descriptions of some variables understood by systemd.

Simple "%"-specifier expansion is supported, see below for a list of supported
specifiers.

DefaultCPUAccounting=, DefaultBlockIOAccounting=, DefaultMemoryAccounting=,
DefaultTasksAccounting=, DefaultIOAccounting=, DefaultIPAccounting=
Configure the default resource accounting settings, as configured per-unit by
CPUAccounting=, BlockIOAccounting=, MemoryAccounting=, TasksAccounting=, IOAccounting=
and IPAccounting=. See systemd.resource-control(5) for details on the per-unit settings.
DefaultTasksAccounting= defaults to yes, DefaultMemoryAccounting= to yes.
DefaultCPUAccounting= defaults to yes if enabling CPU accounting doesn't require the CPU
controller to be enabled (Linux 4.15+ using the unified hierarchy for resource control),
otherwise it defaults to no. The other three settings default to no.

DefaultTasksMax=
Configure the default value for the per-unit TasksMax= setting. See systemd.resource-
control(5) for details. This setting applies to all unit types that support resource
control settings, with the exception of slice units. Defaults to 15% of the minimum of
kernel.pid_max=, kernel.threads-max= and root cgroup pids.max. Kernel has a default value
for kernel.pid_max= and an algorithm of counting in case of more than 32 cores. For
example with the default kernel.pid_max=, DefaultTasksMax= defaults to 4915, but might be
greater in other systems or smaller in OS containers.

DefaultLimitCPU=, DefaultLimitFSIZE=, DefaultLimitDATA=, DefaultLimitSTACK=,
DefaultLimitCORE=, DefaultLimitRSS=, DefaultLimitNOFILE=, DefaultLimitAS=,
DefaultLimitNPROC=, DefaultLimitMEMLOCK=, DefaultLimitLOCKS=, DefaultLimitSIGPENDING=,
DefaultLimitMSGQUEUE=, DefaultLimitNICE=, DefaultLimitRTPRIO=, DefaultLimitRTTIME=
These settings control various default resource limits for processes executed by units.
See setrlimit(2) for details. These settings may be overridden in individual units using
the corresponding LimitXXX= directives and they accept the same parameter syntax, see
systemd.exec(5) for details. Note that these resource limits are only defaults for units,
they are not applied to the service manager process (i.e. PID 1) itself.

Most of these settings are unset, which means the resource limits are inherited from the
kernel or, if invoked in a container, from the container manager. However, the following
have defaults:

• DefaultLimitNOFILE= defaults to "1024:524288".

• DefaultLimitCORE= does not have a default but it is worth mentioning that RLIMIT_CORE
is set to "infinity" by PID 1 which is inherited by its children.

• Note that the service manager internally increases RLIMIT_MEMLOCK for itself, however
the limit is reverted to the original value for child processes forked off.

DefaultOOMPolicy=
Configure the default policy for reacting to processes being killed by the Linux
Out-Of-Memory (OOM) killer. This may be used to pick a global default for the per-unit
OOMPolicy= setting. See systemd.service(5) for details. Note that this default is not
used for services that have Delegate= turned on.

SPECIFIERS
Specifiers may be used in the DefaultEnvironment= and ManagerEnvironment= settings. The
following expansions are understood:

Table 1. Specifiers available
┌──────────┬───────────────────────────┬───────────────────────────┐
│Specifier │ Meaning │ Details │
├──────────┼───────────────────────────┼───────────────────────────┤
│"%a" │ Architecture │ A short string │
│ │ │ identifying the │
│ │ │ architecture of the local │
│ │ │ system. A string such as │
│ │ │ x86, x86-64 or arm64. See │
│ │ │ the architectures defined │
│ │ │ for │
│ │ │ ConditionArchitecture= in │
│ │ │ systemd.unit(5) for a │
│ │ │ full list. │
├──────────┼───────────────────────────┼───────────────────────────┤
│"%A" │ Operating system image │ The operating system │
│ │ version │ image version identifier │
│ │ │ of the running system, as │
│ │ │ read from the │
│ │ │ IMAGE_VERSION= field of │
│ │ │ /etc/os-release. If not │
│ │ │ set, resolves to an empty │
│ │ │ string. See os-release(5) │
│ │ │ for more information. │
├──────────┼───────────────────────────┼───────────────────────────┤
│"%b" │ Boot ID │ The boot ID of the │
│ │ │ running system, formatted │
│ │ │ as string. See random(4) │
│ │ │ for more information. │
├──────────┼───────────────────────────┼───────────────────────────┤
│"%B" │ Operating system build ID │ The operating system │
│ │ │ build identifier of the │
│ │ │ running system, as read │
│ │ │ from the BUILD_ID= field │
│ │ │ of /etc/os-release. If │
│ │ │ not set, resolves to an │
│ │ │ empty string. See os- │
│ │ │ release(5) for more │
│ │ │ information. │
├──────────┼───────────────────────────┼───────────────────────────┤
│"%H" │ Host name │ The hostname of the │
│ │ │ running system. │
├──────────┼───────────────────────────┼───────────────────────────┤
│"%l" │ Short host name │ The hostname of the │
│ │ │ running system, truncated │
│ │ │ at the first dot to │
│ │ │ remove any domain │
│ │ │ component. │
├──────────┼───────────────────────────┼───────────────────────────┤
│"%m" │ Machine ID │ The machine ID of the │
│ │ │ running system, formatted │
│ │ │ as string. See machine- │
│ │ │ id(5) for more │
│ │ │ information. │
├──────────┼───────────────────────────┼───────────────────────────┤
│"%M" │ Operating system image │ The operating system │
│ │ identifier │ image identifier of the │
│ │ │ running system, as read │
│ │ │ from the IMAGE_ID= field │
│ │ │ of /etc/os-release. If │
│ │ │ not set, resolves to an │
│ │ │ empty string. See os- │
│ │ │ release(5) for more │
│ │ │ information. │
├──────────┼───────────────────────────┼───────────────────────────┤
│"%o" │ Operating system ID │ The operating system │
│ │ │ identifier of the running │
│ │ │ system, as read from the │
│ │ │ ID= field of │
│ │ │ /etc/os-release. See os- │
│ │ │ release(5) for more │
│ │ │ information. │
├──────────┼───────────────────────────┼───────────────────────────┤
│"%v" │ Kernel release │ Identical to uname -r │
│ │ │ output. │
├──────────┼───────────────────────────┼───────────────────────────┤
│"%w" │ Operating system version │ The operating system │
│ │ ID │ version identifier of the │
│ │ │ running system, as read │
│ │ │ from the VERSION_ID= │
│ │ │ field of /etc/os-release. │
│ │ │ If not set, resolves to │
│ │ │ an empty string. See os- │
│ │ │ release(5) for more │
│ │ │ information. │
├──────────┼───────────────────────────┼───────────────────────────┤
│"%W" │ Operating system variant │ The operating system │
│ │ ID │ variant identifier of the │
│ │ │ running system, as read │
│ │ │ from the VARIANT_ID= │
│ │ │ field of /etc/os-release. │
│ │ │ If not set, resolves to │
│ │ │ an empty string. See os- │
│ │ │ release(5) for more │
│ │ │ information. │
├──────────┼───────────────────────────┼───────────────────────────┤
│"%T" │ Directory for temporary │ This is either /tmp or │
│ │ files │ the path "$TMPDIR", │
│ │ │ "$TEMP" or "$TMP" are set │
│ │ │ to. (Note that the │
│ │ │ directory may be │
│ │ │ specified without a │
│ │ │ trailing slash.) │
├──────────┼───────────────────────────┼───────────────────────────┤
│"%V" │ Directory for larger and │ This is either /var/tmp │
│ │ persistent temporary │ or the path "$TMPDIR", │
│ │ files │ "$TEMP" or "$TMP" are set │
│ │ │ to. (Note that the │
│ │ │ directory may be │
│ │ │ specified without a │
│ │ │ trailing slash.) │
├──────────┼───────────────────────────┼───────────────────────────┤
│"%%" │ Single percent sign │ Use "%%" in place of "%" │
│ │ │ to specify a single │
│ │ │ percent sign. │
└──────────┴───────────────────────────┴───────────────────────────┘

SEE ALSO
systemd(1), systemd.directives(7), systemd.exec(5), systemd.service(5), environ(7),
capabilities(7)

NOTES
1. No New Privileges Flag
https://www.kernel.org/doc/html/latest/userspace-api/no_new_privs.html

2. ENVIRONMENT
https://systemd.io/ENVIRONMENT

systemd 249 SYSTEMD-SYSTEM.CONF(5)

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