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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</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>/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 the

kernel, from user processes via the libc

<citerefentry><refentrytitle>syslog</refentrytitle><manvolnum>3</manvolnum></citerefentry>

call, from standard input and standard error of system

services or via its native API. It 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>

<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.</para></listitem>

</varlistentry>

<varlistentry>

<term>SIGUSR2</term>

<listitem><para>Request immediate

rotation of the journal

files.</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>

behaviour. 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>

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

<command>pydoc systemd.journal</command>.

</para>

</refsect1>

</refentry>