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<?xml version='1.0'?> <!--*-nxml-*-->
<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
"http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
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You should have received a copy of the GNU Lesser General Public License
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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 project='man-pages'><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>
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