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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)
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
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
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.
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' 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.
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.
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.
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.
/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.
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
1. Users, Groups, UIDs and GIDs on systemd systems
https://systemd.io/UIDS-GIDS
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 2020-08-13. (At that
time, the date of the most recent commit that was found in the repos‐
itory was 2020-08-11.) 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)
Pages that refer to this page: 30-systemd-environment-d-generator(7) , systemd.index(7)