Manual: systemd-journald-audit.socket
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) 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. 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 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.
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. Native Journal Protocol
https://systemd.io/JOURNAL_NATIVE_PROTOCOL
2. Users, Groups, UIDs and GIDs on systemd systems
https://systemd.io/UIDS-GIDS
systemd 259.5 SYSTEMD-JOURNALD.SERVICE(8)