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) 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:
.RS 4
mkdir -p /var/log/journal
systemd-tmpfiles --create --prefix /var/log/journal.RE
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.
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.
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.
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[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:
.RS 4
# setfacl -Rnm g:wheel:rx,d:g:wheel:rx,g:adm:rx,d:g:adm:rx /var/log/journal/.RE
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).
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.
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
Native Journal Protocol
Users, Groups, UIDs and GIDs on systemd systems