systemd-journald@.socket(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)ystemd-journald.serviceYSTEMD-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)

       ·   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/.

       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[1] 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. 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 2020-07-14.  (At that
       time, the date of the most recent commit that was found in the repos‐
       itory was 2020-07-14.)  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 246                                      SYSTEMD-JOURNALD.SERVICE(8)

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