man/systemd-journald.service.xml

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  24 <refentry id="systemd-journald.service">
  25
  26   <refentryinfo>
  27     <title>systemd-journald.service</title>
  28     <productname>systemd</productname>
  29
  30     <authorgroup>
  31       <author>
  32         <contrib>Developer</contrib>
  33         <firstname>Lennart</firstname>
  34         <surname>Poettering</surname>
  35         <email>lennart@poettering.net</email>
  36       </author>
  37     </authorgroup>
  38   </refentryinfo>
  39
  40   <refmeta>
  41     <refentrytitle>systemd-journald.service</refentrytitle>
  42     <manvolnum>8</manvolnum>
  43   </refmeta>
  44
  45   <refnamediv>
  46     <refname>systemd-journald.service</refname>
  47     <refname>systemd-journald.socket</refname>
  48     <refname>systemd-journald-dev-log.socket</refname>
  49     <refname>systemd-journald-audit.socket</refname>
  50     <refname>systemd-journald</refname>
  51     <refpurpose>Journal service</refpurpose>
  52   </refnamediv>
  53
  54   <refsynopsisdiv>
  55     <para><filename>systemd-journald.service</filename></para>
  56     <para><filename>systemd-journald.socket</filename></para>
  57     <para><filename>systemd-journald-dev-log.socket</filename></para>
  58     <para><filename>systemd-journald-audit.socket</filename></para>
  59     <para><filename>/usr/lib/systemd/systemd-journald</filename></para>
  60   </refsynopsisdiv>
  61
  62   <refsect1>
  63     <title>Description</title>
  64
  65     <para><filename>systemd-journald</filename> is a system service
  66     that collects and stores logging data. It creates and maintains
  67     structured, indexed journals based on logging information that is
  68     received from a variety of sources:</para>
  69
  70     <itemizedlist>
  71       <listitem><para>Kernel log messages, via kmsg</para></listitem>
  72
  73       <listitem><para>Simple system log messages, via the libc
  74       <citerefentry project='man-pages'><refentrytitle>syslog</refentrytitle><manvolnum>3</manvolnum></citerefentry>
  75       call</para></listitem>
  76
  77       <listitem><para>Structured system log messages via the native
  78       Journal API, see
  79       <citerefentry><refentrytitle>sd_journal_print</refentrytitle><manvolnum>4</manvolnum></citerefentry></para></listitem>
  80
  81       <listitem><para>Standard output and standard error of system
  82       services</para></listitem>
  83
  84       <listitem><para>Audit records, via the audit
  85       subsystem</para></listitem>
  86     </itemizedlist>
  87
  88     <para>The daemon will implicitly collect numerous metadata fields
  89     for each log messages in a secure and unfakeable way. See
  90     <citerefentry><refentrytitle>systemd.journal-fields</refentrytitle><manvolnum>7</manvolnum></citerefentry>
  91     for more information about the collected metadata.
  92     </para>
  93
  94     <para>Log data collected by the journal is primarily text-based
  95     but can also include binary data where necessary. All objects
  96     stored in the journal can be up to 2^64-1 bytes in size.</para>
  97
  98     <para>By default, the journal stores log data in
  99     <filename>/run/log/journal/</filename>. Since
 100     <filename>/run/</filename> is volatile, log data is lost at
 101     reboot. To make the data persistent, it is sufficient to create
 102     <filename>/var/log/journal/</filename> where
 103     <filename>systemd-journald</filename> will then store the
 104     data:</para>
 105
 106     <programlisting>mkdir -p /var/log/journal
 107 systemd-tmpfiles --create --prefix /var/log/journal</programlisting>
 108
 109     <para><filename>systemd-journald</filename> will forward all
 110     received log messages to the
 111     <constant>AF_UNIX</constant>/<constant>SOCK_DGRAM</constant>
 112     socket <filename>/run/systemd/journal/syslog</filename>, if it
 113     exists, which may be used by Unix syslog daemons to process the
 114     data further.</para>
 115
 116     <para>See
 117     <citerefentry><refentrytitle>journald.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>
 118     for information about the configuration of this service.</para>
 119   </refsect1>
 120
 121   <refsect1>
 122     <title>Signals</title>
 123
 124     <variablelist>
 125       <varlistentry>
 126         <term>SIGUSR1</term>
 127
 128         <listitem><para>Request that journal data from
 129         <filename>/run/</filename> is flushed to
 130         <filename>/var/</filename> in order to make it persistent (if
 131         this is enabled). This must be used after
 132         <filename>/var/</filename> is mounted, as otherwise log data
 133         from <filename>/run</filename> is never flushed to
 134         <filename>/var</filename> regardless of the configuration. The
 135         <command>journalctl --flush</command> command uses this signal
 136         to request flushing of the journal files, and then waits for
 137         the operation to complete. See
 138         <citerefentry><refentrytitle>journalctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>
 139         for details.</para></listitem>
 140       </varlistentry>
 141
 142       <varlistentry>
 143         <term>SIGUSR2</term>
 144
 145         <listitem><para>Request immediate rotation of the journal
 146         files. The <command>journalctl --rotate</command> command uses
 147         this signal to request journal file
 148         rotation.</para></listitem>
 149       </varlistentry>
 150
 151       <varlistentry>
 152         <term>SIGRTMIN+1</term>
 153
 154         <listitem><para>Request that all unwritten log data is written
 155         to disk. The <command>journalctl --sync</command> command uses
 156         this signal to trigger journal synchronization, and then waits
 157         for the operation to complete.</para></listitem>
 158       </varlistentry>
 159     </variablelist>
 160   </refsect1>
 161
 162   <refsect1>
 163     <title>Kernel Command Line</title>
 164
 165     <para>A few configuration parameters from
 166     <filename>journald.conf</filename> may be overridden on the kernel
 167     command line:</para>
 168
 169     <variablelist class='kernel-commandline-options'>
 170       <varlistentry>
 171         <term><varname>systemd.journald.forward_to_syslog=</varname></term>
 172         <term><varname>systemd.journald.forward_to_kmsg=</varname></term>
 173         <term><varname>systemd.journald.forward_to_console=</varname></term>
 174         <term><varname>systemd.journald.forward_to_wall=</varname></term>
 175
 176         <listitem><para>Enables/disables forwarding of collected log
 177         messages to syslog, the kernel log buffer, the system console
 178         or wall.
 179         </para>
 180
 181         <para>See
 182         <citerefentry><refentrytitle>journald.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>
 183         for information about these settings.</para>
 184         </listitem>
 185
 186       </varlistentry>
 187     </variablelist>
 188   </refsect1>
 189
 190   <refsect1>
 191     <title>Access Control</title>
 192
 193     <para>Journal files are, by default, owned and readable by the
 194     <literal>systemd-journal</literal> system group but are not
 195     writable. Adding a user to this group thus enables her/him to read
 196     the journal files.</para>
 197
 198     <para>By default, each logged in user will get her/his own set of
 199     journal files in <filename>/var/log/journal/</filename>. These
 200     files will not be owned by the user, however, in order to avoid
 201     that the user can write to them directly. Instead, file system
 202     ACLs are used to ensure the user gets read access only.</para>
 203
 204     <para>Additional users and groups may be granted access to journal
 205     files via file system access control lists (ACL). Distributions
 206     and administrators may choose to grant read access to all members
 207     of the <literal>wheel</literal> and <literal>adm</literal> system
 208     groups with a command such as the following:</para>
 209
 210     <programlisting># setfacl -Rnm g:wheel:rx,d:g:wheel:rx,g:adm:rx,d:g:adm:rx /var/log/journal/</programlisting>
 211
 212     <para>Note that this command will update the ACLs both for
 213     existing journal files and for future journal files created in the
 214     <filename>/var/log/journal/</filename> directory.</para>
 215   </refsect1>
 216
 217   <refsect1>
 218     <title>Files</title>
 219
 220     <variablelist>
 221       <varlistentry>
 222         <term><filename>/etc/systemd/journald.conf</filename></term>
 223
 224         <listitem><para>Configure
 225         <command>systemd-journald</command>
 226         behavior. See
 227         <citerefentry><refentrytitle>journald.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>.
 228         </para></listitem>
 229       </varlistentry>
 230
 231       <varlistentry>
 232         <term><filename>/run/log/journal/<replaceable>machine-id</replaceable>/*.journal</filename></term>
 233         <term><filename>/run/log/journal/<replaceable>machine-id</replaceable>/*.journal~</filename></term>
 234         <term><filename>/var/log/journal/<replaceable>machine-id</replaceable>/*.journal</filename></term>
 235         <term><filename>/var/log/journal/<replaceable>machine-id</replaceable>/*.journal~</filename></term>
 236
 237         <listitem><para><command>systemd-journald</command> writes
 238         entries to files in
 239         <filename>/run/log/journal/<replaceable>machine-id</replaceable>/</filename>
 240         or
 241         <filename>/var/log/journal/<replaceable>machine-id</replaceable>/</filename>
 242         with the <literal>.journal</literal> suffix. If the daemon is
 243         stopped uncleanly, or if the files are found to be corrupted,
 244         they are renamed using the <literal>.journal~</literal>
 245         suffix, and <command>systemd-journald</command> starts writing
 246         to a new file. <filename>/run</filename> is used when
 247         <filename>/var/log/journal</filename> is not available, or
 248         when <option>Storage=volatile</option> is set in the
 249         <citerefentry><refentrytitle>journald.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>
 250         configuration file.</para></listitem>
 251       </varlistentry>
 252
 253       <varlistentry>
 254         <term><filename>/dev/kmsg</filename></term>
 255         <term><filename>/dev/log</filename></term>
 256         <term><filename>/run/systemd/journal/dev-log</filename></term>
 257         <term><filename>/run/systemd/journal/socket</filename></term>
 258         <term><filename>/run/systemd/journal/stdout</filename></term>
 259
 260         <listitem><para>Sockets and other paths that
 261         <command>systemd-journald</command> will listen on that are
 262         visible in the file system. In addition to these, journald can
 263         listen for audit events using netlink.</para></listitem>
 264       </varlistentry>
 265     </variablelist>
 266   </refsect1>
 267
 268   <refsect1>
 269     <title>See Also</title>
 270     <para>
 271       <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
 272       <citerefentry><refentrytitle>journalctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
 273       <citerefentry><refentrytitle>journald.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 274       <citerefentry><refentrytitle>systemd.journal-fields</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
 275       <citerefentry><refentrytitle>sd-journal</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 276       <citerefentry><refentrytitle>systemd-coredump</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
 277       <citerefentry project='die-net'><refentrytitle>setfacl</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
 278       <citerefentry><refentrytitle>sd_journal_print</refentrytitle><manvolnum>4</manvolnum></citerefentry>,
 279       <command>pydoc systemd.journal</command>
 280     </para>
 281   </refsect1>
 282
 283 </refentry>