systemd-journald.socket(8) - man - phpMan

SYSTEMD-JOURNALD.SERVICE(8)           systemd-journald.service           SYSTEMD-JOURNALD.SERVICE(8)



NAME
       systemd-journald.service, systemd-journald.socket, systemd-journald-dev-log.socket, systemd-
       journald-audit.socket, systemd-journald@.service, systemd-journald@.socket, systemd-journald-
       varlink@.socket, systemd-journald - Journal service

SYNOPSIS
       systemd-journald.service

       systemd-journald.socket

       systemd-journald-dev-log.socket

       systemd-journald-audit.socket

       systemd-journald@.service

       systemd-journald@.socket

       systemd-journald-varlink@.socket

       /lib/systemd/systemd-journald

DESCRIPTION
       systemd-journald is a system service that collects and stores logging data. It creates and
       maintains structured, indexed journals based on logging information that is received from a
       variety of sources:

       •   Kernel log messages, via kmsg

       •   Simple system log messages, via the libc syslog(3) call

       •   Structured system log messages via the native Journal API, see sd_journal_print(3) and
           Native Journal Protocol[1]

       •   Standard output and standard error of service units. For further details see below.

       •   Audit records, originating from the kernel audit subsystem

       The daemon will implicitly collect numerous metadata fields for each log messages in a secure
       and unfakeable way. See systemd.journal-fields(7) for more information about the collected
       metadata.

       Log data collected by the journal is primarily text-based but can also include binary data
       where necessary. Individual fields making up a log record stored in the journal may be up to
       2^64-1 bytes in size.

       The journal service stores log data either persistently below /var/log/journal or in a
       volatile way below /run/log/journal/ (in the latter case it is lost at reboot). By default,
       log data is stored persistently if /var/log/journal/ exists during boot, with an implicit
       fallback to volatile storage otherwise. Use Storage= in journald.conf(5) to configure where
       log data is placed, independently of the existence of /var/log/journal/.

       Note that journald will initially use volatile storage, until a call to journalctl --flush
       (or sending SIGUSR1 to journald) will cause it to switch to persistent logging (under the
       conditions mentioned above). This is done automatically on boot via
       "systemd-journal-flush.service".

       On systems where /var/log/journal/ does not exist yet but where persistent logging is desired
       (and the default journald.conf is used), it is sufficient to create the directory, and ensure
       it has the correct access modes and ownership:

           mkdir -p /var/log/journal
           systemd-tmpfiles --create --prefix /var/log/journal

       See journald.conf(5) for information about the configuration of this service.

STREAM LOGGING
       The systemd service manager invokes all service processes with standard output and standard
       error connected to the journal by default. This behaviour may be altered via the
       StandardOutput=/StandardError= unit file settings, see systemd.exec(5) for details. The
       journal converts the log byte stream received this way into individual log records, splitting
       the stream at newline ("\n", ASCII 10) and NUL bytes.

       If systemd-journald.service is stopped, the stream connections associated with all services
       are terminated. Further writes to those streams by the service will result in EPIPE errors.
       In order to react gracefully in this case it is recommended that programs logging to standard
       output/error ignore such errors. If the SIGPIPE UNIX signal handler is not blocked or turned
       off, such write attempts will also result in such process signals being generated, see
       signal(7). To mitigate this issue, systemd service manager explicitly turns off the SIGPIPE
       signal for all invoked processes by default (this may be changed for each unit individually
       via the IgnoreSIGPIPE= option, see systemd.exec(5) for details). After the standard
       output/standard error streams have been terminated they may not be recovered until the
       services they are associated with are restarted. Note that during normal operation,
       systemd-journald.service stores copies of the file descriptors for those streams in the
       service manager. If systemd-journald.service is restarted using systemctl restart or
       equivalent operation instead of a pair of separate systemctl stop and systemctl start
       commands (or equivalent operations), these stream connections are not terminated and survive
       the restart. It is thus safe to restart systemd-journald.service, but stopping it is not
       recommended.

       Note that the log record metadata for records transferred via such standard output/error
       streams reflect the metadata of the peer the stream was originally created for. If the stream
       connection is passed on to other processes (such as further child processes forked off the
       main service process), the log records will not reflect their metadata, but will continue to
       describe the original process. This is different from the other logging transports listed
       above, which are inherently record based and where the metadata is always associated with the
       individual record.

       In addition to the implicit standard output/error logging of services, stream logging is also
       available via the systemd-cat(1) command line tool.

       Currently, the number of parallel log streams systemd-journald will accept is limited to
       4096. When this limit is reached further log streams may be established but will receive
       EPIPE right from the beginning.

JOURNAL NAMESPACES
       Journal 'namespaces' are both a mechanism for logically isolating the log stream of projects
       consisting of one or more services from the rest of the system and a mechanism for improving
       performance. Multiple journal namespaces may exist simultaneously, each defining its own,
       independent log stream managed by its own instance of systemd-journald. Namespaces are
       independent of each other, both in the data store and in the IPC interface. By default only a
       single 'default' namespace exists, managed by systemd-journald.service (and its associated
       socket units). Additional namespaces are created by starting an instance of the
       systemd-journald@.service service template. The instance name is the namespace identifier,
       which is a short string used for referencing the journal namespace. Service units may be
       assigned to a specific journal namespace through the LogNamespace= unit file setting, see
       systemd.exec(5) for details. The --namespace= switch of journalctl(1) may be used to view the
       log stream of a specific namespace. If the switch is not used the log stream of the default
       namespace is shown, i.e. log data from other namespaces is not visible.

       Services associated with a specific log namespace may log via syslog, the native logging
       protocol of the journal and via stdout/stderr; the logging from all three transports is
       associated with the namespace.

       By default only the default namespace will collect kernel and audit log messages.

       The systemd-journald instance of the default namespace is configured through
       /etc/systemd/journald.conf (see below), while the other instances are configured through
       /etc/systemd/journald@NAMESPACE.conf. The journal log data for the default namespace is
       placed in /var/log/journal/MACHINE_ID (see below) while the data for the other namespaces is
       located in /var/log/journal/MACHINE_ID.NAMESPACE.

SIGNALS
       SIGUSR1
           Request that journal data from /run/ is flushed to /var/ in order to make it persistent
           (if this is enabled). This must be used after /var/ is mounted, as otherwise log data
           from /run/ is never flushed to /var/ regardless of the configuration. Use the journalctl
           --flush command to request flushing of the journal files, and wait for the operation to
           complete. See journalctl(1) for details.

       SIGUSR2
           Request immediate rotation of the journal files. Use the journalctl --rotate command to
           request journal file rotation, and wait for the operation to complete.

       SIGRTMIN+1
           Request that all unwritten log data is written to disk. Use the journalctl --sync command
           to trigger journal synchronization, and wait for the operation to complete.

KERNEL COMMAND LINE
       A few configuration parameters from journald.conf may be overridden on the kernel command
       line:

       systemd.journald.forward_to_syslog=, systemd.journald.forward_to_kmsg=,
       systemd.journald.forward_to_console=, systemd.journald.forward_to_wall=
           Enables/disables forwarding of collected log messages to syslog, the kernel log buffer,
           the system console or wall.

           See journald.conf(5) for information about these settings.

       Note that these kernel command line options are only honoured by the default namespace, see
       above.

ACCESS CONTROL
       Journal files are, by default, owned and readable by the "systemd-journal" system group but
       are not writable. Adding a user to this group thus enables them to read the journal files.

       By default, each user, with a UID outside the range of system users, dynamic service users,
       and the nobody user, will get their own set of journal files in /var/log/journal/. See Users,
       Groups, UIDs and GIDs on systemd systems[2] for more details about UID ranges. These journal
       files will not be owned by the user, however, in order to avoid that the user can write to
       them directly. Instead, file system ACLs are used to ensure the user gets read access only.

       Additional users and groups may be granted access to journal files via file system access
       control lists (ACL). Distributions and administrators may choose to grant read access to all
       members of the "wheel" and "adm" system groups with a command such as the following:

           # setfacl -Rnm g:wheel:rx,d:g:wheel:rx,g:adm:rx,d:g:adm:rx /var/log/journal/

       Note that this command will update the ACLs both for existing journal files and for future
       journal files created in the /var/log/journal/ directory.

FILES
       /etc/systemd/journald.conf
           Configure systemd-journald behavior. See journald.conf(5).

       /run/log/journal/machine-id/*.journal, /run/log/journal/machine-id/*.journal~,
       /var/log/journal/machine-id/*.journal, /var/log/journal/machine-id/*.journal~
           systemd-journald writes entries to files in /run/log/journal/machine-id/ or
           /var/log/journal/machine-id/ with the ".journal" suffix. If the daemon is stopped
           uncleanly, or if the files are found to be corrupted, they are renamed using the
           ".journal~" suffix, and systemd-journald starts writing to a new file.  /run/ is used
           when /var/log/journal is not available, or when Storage=volatile is set in the
           journald.conf(5) configuration file.

           When systemd-journald ceases writing to a journal file, it will be renamed to
           "original-name@suffix.journal" (or "original-name@suffix.journal~"). Such files are
           "archived" and will not be written to any more.

           In general, it is safe to read or copy any journal file (active or archived).
           journalctl(1) and the functions in the sd-journal(3) library should be able to read all
           entries that have been fully written.

           systemd-journald will automatically remove the oldest archived journal files to limit
           disk use. See SystemMaxUse= and related settings in journald.conf(5).

       /dev/kmsg, /dev/log, /run/systemd/journal/dev-log, /run/systemd/journal/socket,
       /run/systemd/journal/stdout
           Sockets and other file node paths that systemd-journald will listen on and are visible in
           the file system. In addition to these, systemd-journald can listen for audit events using
           netlink(7).

       If journal namespacing is used these paths are slightly altered to include a namespace
       identifier, see above.

SEE ALSO
       systemd(1), journalctl(1), journald.conf(5), systemd.journal-fields(7), sd-journal(3),
       systemd-coredump(8), setfacl(1), sd_journal_print(3), pydoc systemd.journal

NOTES
        1. Native Journal Protocol
           https://systemd.io/JOURNAL_NATIVE_PROTOCOL

        2. Users, Groups, UIDs and GIDs on systemd systems
           https://systemd.io/UIDS-GIDS



systemd 249                                                              SYSTEMD-JOURNALD.SERVICE(8)