Ubuntu Manpage: systemd-journald.service, systemd-journald.socket, systemd-journald-dev-log.socket,

Provided by: systemd_237-3ubuntu10.57_amd64

NAME

       systemd-journald.service, systemd-journald.socket, systemd-journald-dev-log.socket,
       systemd-journald-audit.socket, systemd-journald - Journal service

SYNOPSIS

       systemd-journald.service

       systemd-journald.socket

       systemd-journald-dev-log.socket

       systemd-journald-audit.socket

       /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(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. 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.

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.

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.
           The journalctl --flush command uses this signal to request flushing of the journal
           files, and then waits for the operation to complete. See journalctl(1) for details.

       SIGUSR2
           Request immediate rotation of the journal files. The journalctl --rotate command uses
           this signal to request journal file rotation.

       SIGRTMIN+1
           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.

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.

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 her/him to read the journal
       files.

       By default, each logged in user will get her/his own set of journal files in
       /var/log/journal/. These 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).

       /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.

       /dev/kmsg, /dev/log, /run/systemd/journal/dev-log, /run/systemd/journal/socket,
       /run/systemd/journal/stdout
           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.