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<refentry id="systemd-journald.service">

<refentryinfo>

<title>systemd-journald.service</title>

<productname>systemd</productname>

<authorgroup>

<author>

<contrib>Developer</contrib>

<firstname>Lennart</firstname>

<surname>Poettering</surname>

<email>lennart@poettering.net</email>

</author>

</authorgroup>

</refentryinfo>

<refmeta>

<refentrytitle>systemd-journald.service</refentrytitle>

<manvolnum>8</manvolnum>

</refmeta>

<refnamediv>

<refname>systemd-journald.service</refname>

<refname>systemd-journald.socket</refname>

<refname>systemd-journald-dev-log.socket</refname>

<refname>systemd-journald-audit.socket</refname>

<refname>systemd-journald</refname>

<refpurpose>Journal service</refpurpose>

</refnamediv>

<refsynopsisdiv>

<para><filename>systemd-journald.service</filename></para>

<para><filename>systemd-journald.socket</filename></para>

<para><filename>systemd-journald-dev-log.socket</filename></para>

<para><filename>systemd-journald-audit.socket</filename></para>

<para><filename>/usr/lib/systemd/systemd-journald</filename></para>

</refsynopsisdiv>

<refsect1>

<title>Description</title>

<para><filename>systemd-journald</filename> 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:</para>

<itemizedlist>

<listitem><para>Kernel log messages, via kmsg</para></listitem>

<listitem><para>Simple system log messages, via the libc

<citerefentry project='man-pages'><refentrytitle>syslog</refentrytitle><manvolnum>3</manvolnum></citerefentry>

call</para></listitem>

<listitem><para>Structured system log messages via the native

Journal API, see

<citerefentry><refentrytitle>sd_journal_print</refentrytitle><manvolnum>4</manvolnum></citerefentry></para></listitem>

<listitem><para>Standard output and standard error of system

services</para></listitem>

<listitem><para>Audit records, via the audit

subsystem</para></listitem>

</itemizedlist>

<para>The daemon will implicitly collect numerous metadata fields

for each log messages in a secure and unfakeable way. See

<citerefentry><refentrytitle>systemd.journal-fields</refentrytitle><manvolnum>7</manvolnum></citerefentry>

for more information about the collected metadata.

</para>

<para>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.</para>

<para>By default, the journal stores log data in

<filename>/run/log/journal/</filename>. Since

<filename>/run/</filename> is volatile, log data is lost at

reboot. To make the data persistent, it is sufficient to create

<filename>/var/log/journal/</filename> where

<filename>systemd-journald</filename> will then store the

data:</para>

<programlisting>mkdir -p /var/log/journal

systemd-tmpfiles --create --prefix /var/log/journal</programlisting>

<para><filename>systemd-journald</filename> will forward all

received log messages to the

<constant>AF_UNIX</constant>/<constant>SOCK_DGRAM</constant>

socket <filename>/run/systemd/journal/syslog</filename>, if it

exists, which may be used by Unix syslog daemons to process the

data further.</para>

<para>See

<citerefentry><refentrytitle>journald.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>

for information about the configuration of this service.</para>

</refsect1>

<refsect1>

<title>Signals</title>

<variablelist>

<varlistentry>

<term>SIGUSR1</term>

<listitem><para>Request that journal data from

<filename>/run/</filename> is flushed to

<filename>/var/</filename> in order to make it persistent (if

this is enabled). This must be used after

<filename>/var/</filename> is mounted, as otherwise log data

from <filename>/run</filename> is never flushed to

<filename>/var</filename> regardless of the configuration. The

<command>journalctl --flush</command> command uses this signal

to request flushing of the journal files, and then waits for

the operation to complete. See

<citerefentry><refentrytitle>journalctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>

for details.</para></listitem>

</varlistentry>

<varlistentry>

<term>SIGUSR2</term>

<listitem><para>Request immediate rotation of the journal

files. The <command>journalctl --rotate</command> command uses

this signal to request journal file

rotation.</para></listitem>

</varlistentry>

<varlistentry>

<term>SIGRTMIN+1</term>

<listitem><para>Request that all unwritten log data is written

to disk. The <command>journalctl --sync</command> command uses

this signal to trigger journal synchronization, and then waits

for the operation to complete.</para></listitem>

</varlistentry>

</variablelist>

</refsect1>

<refsect1>

<title>Kernel Command Line</title>

<para>A few configuration parameters from

<filename>journald.conf</filename> may be overridden on the kernel

command line:</para>

<variablelist class='kernel-commandline-options'>

<varlistentry>

<term><varname>systemd.journald.forward_to_syslog=</varname></term>

<term><varname>systemd.journald.forward_to_kmsg=</varname></term>

<term><varname>systemd.journald.forward_to_console=</varname></term>

<term><varname>systemd.journald.forward_to_wall=</varname></term>

<listitem><para>Enables/disables forwarding of collected log

messages to syslog, the kernel log buffer, the system console

or wall.

</para>

<para>See

<citerefentry><refentrytitle>journald.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>

for information about these settings.</para>

</listitem>

</varlistentry>

</variablelist>

</refsect1>

<refsect1>

<title>Access Control</title>

<para>Journal files are, by default, owned and readable by the

<literal>systemd-journal</literal> system group but are not

writable. Adding a user to this group thus enables her/him to read

the journal files.</para>

<para>By default, each logged in user will get her/his own set of

journal files in <filename>/var/log/journal/</filename>. 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.</para>

<para>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 <literal>wheel</literal> and <literal>adm</literal> system

groups with a command such as the following:</para>

<programlisting># setfacl -Rnm g:wheel:rx,d:g:wheel:rx,g:adm:rx,d:g:adm:rx /var/log/journal/</programlisting>

<para>Note that this command will update the ACLs both for

existing journal files and for future journal files created in the

<filename>/var/log/journal/</filename> directory.</para>

</refsect1>

<refsect1>

<title>Files</title>

<variablelist>

<varlistentry>

<term><filename>/etc/systemd/journald.conf</filename></term>

<listitem><para>Configure

<command>systemd-journald</command>

behavior. See

<citerefentry><refentrytitle>journald.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>.

</para></listitem>

</varlistentry>

<varlistentry>

<term><filename>/run/log/journal/<replaceable>machine-id</replaceable>/*.journal</filename></term>

<term><filename>/run/log/journal/<replaceable>machine-id</replaceable>/*.journal~</filename></term>

<term><filename>/var/log/journal/<replaceable>machine-id</replaceable>/*.journal</filename></term>

<term><filename>/var/log/journal/<replaceable>machine-id</replaceable>/*.journal~</filename></term>

<listitem><para><command>systemd-journald</command> writes

entries to files in

<filename>/run/log/journal/<replaceable>machine-id</replaceable>/</filename>

or

<filename>/var/log/journal/<replaceable>machine-id</replaceable>/</filename>

with the <literal>.journal</literal> suffix. If the daemon is

stopped uncleanly, or if the files are found to be corrupted,

they are renamed using the <literal>.journal~</literal>

suffix, and <command>systemd-journald</command> starts writing

to a new file. <filename>/run</filename> is used when

<filename>/var/log/journal</filename> is not available, or

when <option>Storage=volatile</option> is set in the

<citerefentry><refentrytitle>journald.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>

configuration file.</para></listitem>

</varlistentry>

<varlistentry>

<term><filename>/dev/kmsg</filename></term>

<term><filename>/dev/log</filename></term>

<term><filename>/run/systemd/journal/dev-log</filename></term>

<term><filename>/run/systemd/journal/socket</filename></term>

<term><filename>/run/systemd/journal/stdout</filename></term>

<listitem><para>Sockets and other paths that

<command>systemd-journald</command> will listen on that are

visible in the file system. In addition to these, journald can

listen for audit events using netlink.</para></listitem>

</varlistentry>

</variablelist>

</refsect1>

<refsect1>

<title>See Also</title>

<para>

<citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,

<citerefentry><refentrytitle>journalctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>,

<citerefentry><refentrytitle>journald.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>,

<citerefentry><refentrytitle>systemd.journal-fields</refentrytitle><manvolnum>7</manvolnum></citerefentry>,

<citerefentry><refentrytitle>sd-journal</refentrytitle><manvolnum>3</manvolnum></citerefentry>,

<citerefentry><refentrytitle>systemd-coredump</refentrytitle><manvolnum>8</manvolnum></citerefentry>,

<citerefentry project='die-net'><refentrytitle>setfacl</refentrytitle><manvolnum>1</manvolnum></citerefentry>,

<citerefentry><refentrytitle>sd_journal_print</refentrytitle><manvolnum>4</manvolnum></citerefentry>,

<command>pydoc systemd.journal</command>

</para>

</refsect1>

</refentry>