systemd-journald.service(8) — Linux manual page

NAME | SYNOPSIS | DESCRIPTION | STREAM LOGGING | JOURNAL NAMESPACES | SIGNALS | KERNEL COMMAND LINE | ACCESS CONTROL | FILES | SEE ALSO | NOTES | COLOPHON

SYSTEMD-JOURNALD.SERVICE(8)temd-journald.serviceTEMD-JOURNALD.SERVICE(8)

NAME         top

       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         top

       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

       /usr/lib/systemd/systemd-journald

DESCRIPTION         top

       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         top

       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         top

       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         top

       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         top

       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         top

       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         top

       /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         top

       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         top

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

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

COLOPHON         top

       This page is part of the systemd (systemd system and service
       manager) project.  Information about the project can be found at
       ⟨http://www.freedesktop.org/wiki/Software/systemd⟩.  If you have
       a bug report for this manual page, see
       ⟨http://www.freedesktop.org/wiki/Software/systemd/#bugreports⟩.
       This page was obtained from the project's upstream Git repository
       ⟨https://github.com/systemd/systemd.git⟩ on 2021-08-27.  (At that
       time, the date of the most recent commit that was found in the
       repository was 2021-08-27.)  If you discover any rendering
       problems in this HTML version of the page, or you believe there
       is a better or more up-to-date source for the page, or you have
       corrections or improvements to the information in this COLOPHON
       (which is not part of the original manual page), send a mail to
       man-pages@man7.org

systemd 249                                  SYSTEMD-JOURNALD.SERVICE(8)

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