systemd-journald.service, systemd-journald.socket, systemd-journald-dev-log.socket, systemd-journald-audit.socket, systemd-journald — Journal service
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
Structured system log messages via the native Journal API, see sd_journal_print(4)
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. All objects stored in the journal can be up to 2^64-1 bytes in size.
By default, the journal stores log data in
/run/ is volatile, log data is lost at
reboot. To make the data persistent, it is sufficient to create
systemd-journald will then store the
mkdir -p /var/log/journal systemd-tmpfiles --create --prefix /var/log/journal
See journald.conf(5) for information about the configuration of this service.
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
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
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
errors. In order to react gracefully in this case it is recommended that programs logging to standard output/error
ignore such errors. If the 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
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 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 receieve
EPIPE right from the beginning.
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
/run is never flushed to
/var regardless of the configuration. The
journalctl --flush command uses this signal
to request flushing of the journal files, and then waits for
the operation to complete. See
Request immediate rotation of the journal files. The journalctl --rotate command uses this signal to request journal file rotation.
Request that all unwritten log data is written to disk. The journalctl --sync command uses this signal to trigger journal synchronization, and then waits for the operation to complete.
A few configuration parameters from
journald.conf may be overridden on the kernel
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.
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 her/him to read
the journal files.
By default, each logged in user will get her/his own set of
journal files in
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 "
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
Configure systemd-journald behavior. See journald.conf(5).
entries to files in
with the "
.journal" suffix. If the daemon is
stopped uncleanly, or if the files are found to be corrupted,
they are renamed using the "
suffix, and systemd-journald starts writing
to a new file.
/run is used when
/var/log/journal is not available, or
Storage=volatile is set in the
Sockets and other paths that systemd-journald will listen on that are visible in the file system. In addition to these, journald can listen for audit events using netlink.