# systemd-journald.service

## 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) 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. Seesystemd.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 2⁶⁴-1 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(3), 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.
    
               Added in version 186.
    
           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.
    
               Added in version 186.
    
           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.
    
               Added in version 228.
    
           SIGHUP
               Upon reception of the **SIGHUP** process signal **systemd-journald**
               will reload its configuration values and update the kernel log
               buffer and journals to reflect the new configuration. If
               _ReadKmsg=_ has changed, the kernel log buffer will be flushed
               and updated as part of the reload. The active journal (e.g.,
               persistent, volatile) will continue to be used with the
               updated configuration. However, if the storage mode has
               changed from persistent to volatile and the current journal in
               use is the persistent journal, then the active journal will be
               switched to the volatile journal.
    
               Added in version 258.
    


## CREDENTIALS



           **systemd-journald** supports the service credentials logic as
           implemented by _ImportCredential=_ /_LoadCredential=_ /_SetCredential=_
           (see systemd.exec(5) for details). The following credentials are
           used when passed in:
    
           _journal.forward_to_socket_
               May contain a socket address to which logs should be
               forwarded. See _ForwardToSocket=_ in journald.conf(5).
    
               Added in version 256.
    
           _journal.storage_
               May be used to specify where journal files should be stored.
               See _Storage=_ in journald.conf(5).
    
               Added in version 256.
    


## 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.
    
               Added in version 186.
    
           _systemd.journald.max_level_store=_ ,
           _systemd.journald.max_level_syslog=_ ,
           _systemd.journald.max_level_kmsg=_ ,
           _systemd.journald.max_level_console=_ ,
           _systemd.journald.max_level_wall=_ ,
           _systemd.journald.max_level_socket=_
               Controls the maximum log level of messages that are stored in
               the journal, forwarded to syslog(3), kmsg, the console,
               wall(1), or a socket. This kernel command line options
               override the settings of the same names in the
               journald.conf(5) file.
    
               Added in version 232.
    
           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).
    
               Added in version 206.
    
           /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).
    
               Added in version 206.
    
           /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), depending on whether
               "systemd-journald-audit.socket" is enabled or not.
    
               Added in version 228.
    
           If journal namespacing is used these paths are slightly altered to
           include a namespace identifier, see above.
    


## 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
    


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