systemd-journald.service

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

       /usr/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)

       •   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
       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 247                                          SYSTEMD-JOURNALD.SERVICE(8)