systemd-journald

SYSTEMD-JOURNALD.SERVICE(8)systemd-journald.serviceSYSTEMD-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:

       o   Kernel log messages, via kmsg

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

       o   Structured system log messages via the native Journal API, see
           sd_journal_print(3)

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

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

systemd 245                                        SYSTEMD-JOURNALD.SERVICE(8)