man/systemd-journald.service.xml

   1 <?xml version='1.0'?> <!--*-nxml-*-->
   2 <!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
   3         "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
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   6   This file is part of systemd.
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   8   Copyright 2010 Lennart Poettering
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  23
  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</refname>
  49                 <refpurpose>Journal service</refpurpose>
  50         </refnamediv>
  51
  52         <refsynopsisdiv>
  53                 <para><filename>systemd-journald.service</filename></para>
  54                 <para><filename>systemd-journald.socket</filename></para>
  55                 <para><filename>/usr/lib/systemd/systemd-journald</filename></para>
  56         </refsynopsisdiv>
  57
  58         <refsect1>
  59                 <title>Description</title>
  60
  61                 <para><filename>systemd-journald</filename> is a
  62                 system service that collects and stores logging data.
  63                 It creates and maintains structured, indexed journals
  64                 based on logging information that is received from the
  65                 kernel, from user processes via the libc
  66                 <citerefentry><refentrytitle>syslog</refentrytitle><manvolnum>3</manvolnum></citerefentry>
  67                 call, from standard input and standard error of system
  68                 services or via its native API. It will implicitly
  69                 collect numerous metadata fields for each log
  70                 messages in a secure and unfakeable way. See
  71                 <citerefentry><refentrytitle>systemd.journal-fields</refentrytitle><manvolnum>7</manvolnum></citerefentry>
  72                 for more information about the collected metadata.
  73                 </para>
  74
  75                 <para>Log data collected by the journal is primarily
  76                 text-based but can also include binary data where
  77                 necessary. All objects stored in the journal can be up
  78                 to 2^64-1 bytes in size.</para>
  79
  80                 <para>By default, the journal stores log data in
  81                 <filename>/run/log/journal/</filename>. Since
  82                 <filename>/run/</filename> is volatile, log data is
  83                 lost at reboot. To make the data persistent, it
  84                 is sufficient to create
  85                 <filename>/var/log/journal/</filename> where
  86                 <filename>systemd-journald</filename> will then store
  87                 the data.</para>
  88
  89                 <para><filename>systemd-journald</filename> will
  90                 forward all received log messages to the <constant>AF_UNIX</constant>
  91                 <constant>SOCK_DGRAM</constant> socket
  92                 <filename>/run/systemd/journal/syslog</filename>, if it exists, which
  93                 may be used by Unix syslog daemons to process the data
  94                 further.</para>
  95
  96                 <para>See
  97                 <citerefentry><refentrytitle>journald.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>
  98                 for information about the configuration of this
  99                 service.</para>
 100         </refsect1>
 101
 102         <refsect1>
 103                 <title>Signals</title>
 104
 105                 <variablelist>
 106                         <varlistentry>
 107                                 <term>SIGUSR1</term>
 108
 109                                 <listitem><para>Request that journal
 110                                 data from <filename>/run/</filename>
 111                                 is flushed to
 112                                 <filename>/var/</filename> in order to
 113                                 make it persistent (if this is
 114                                 enabled). This must be used after
 115                                 <filename>/var/</filename> is mounted,
 116                                 as otherwise log data from
 117                                 <filename>/run</filename> is never
 118                                 flushed to <filename>/var</filename>
 119                                 regardless of the
 120                                 configuration.</para></listitem>
 121                         </varlistentry>
 122
 123                         <varlistentry>
 124                                 <term>SIGUSR2</term>
 125
 126                                 <listitem><para>Request immediate
 127                                 rotation of the journal
 128                                 files.</para></listitem>
 129                         </varlistentry>
 130                 </variablelist>
 131         </refsect1>
 132
 133         <refsect1>
 134                 <title>Kernel Command Line</title>
 135
 136                 <para>A few configuration parameters from
 137                 <filename>journald.conf</filename> may be overridden on
 138                 the kernel command line:</para>
 139
 140                 <variablelist class='kernel-commandline-options'>
 141                         <varlistentry>
 142                                 <term><varname>systemd.journald.forward_to_syslog=</varname></term>
 143                                 <term><varname>systemd.journald.forward_to_kmsg=</varname></term>
 144                                 <term><varname>systemd.journald.forward_to_console=</varname></term>
 145
 146                                 <listitem><para>Enables/disables
 147                                 forwarding of collected log messages
 148                                 to syslog, the kernel log buffer or
 149                                 the system console.
 150                                 </para>
 151
 152                                 <para>See
 153                                 <citerefentry><refentrytitle>journald.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>
 154                                 for information about these settings.</para>
 155                                 </listitem>
 156
 157                         </varlistentry>
 158                 </variablelist>
 159         </refsect1>
 160
 161         <refsect1>
 162                 <title>Access Control</title>
 163
 164                 <para>Journal files are, by default, owned and readable
 165                 by the <literal>systemd-journal</literal> system group
 166                 but are not writable. Adding a user to this group thus
 167                 enables her/him to read the journal files.</para>
 168
 169                 <para>By default, each logged in user will get her/his
 170                 own set of journal files in
 171                 <filename>/var/log/journal/</filename>. These files
 172                 will not be owned by the user, however, in order to
 173                 avoid that the user can write to them
 174                 directly. Instead, file system ACLs are used to ensure
 175                 the user gets read access only.</para>
 176
 177                 <para>Additional users and groups may be granted
 178                 access to journal files via file system access control
 179                 lists (ACL). Distributions and administrators may
 180                 choose to grant read access to all members of the
 181                 <literal>wheel</literal> and <literal>adm</literal>
 182                 system groups with a command such as the
 183                 following:</para>
 184
 185                 <programlisting># setfacl -Rnm g:wheel:rx,d:g:wheel:rx,g:adm:rx,d:g:adm:rx /var/log/journal/</programlisting>
 186
 187                 <para>Note that this command will update the ACLs both
 188                 for existing journal files and for future journal
 189                 files created in the
 190                 <filename>/var/log/journal/</filename>
 191                 directory.</para>
 192         </refsect1>
 193
 194         <refsect1>
 195                 <title>Files</title>
 196
 197                 <variablelist>
 198                         <varlistentry>
 199                                 <term><filename>/etc/systemd/journald.conf</filename></term>
 200
 201                                 <listitem><para>Configure
 202                                 <command>systemd-journald</command>
 203                                 behaviour. See
 204                                 <citerefentry><refentrytitle>journald.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>.
 205                                 </para></listitem>
 206                         </varlistentry>
 207
 208                         <varlistentry>
 209                                 <term><filename>/run/log/journal/<replaceable>machine-id</replaceable>/*.journal</filename></term>
 210                                 <term><filename>/run/log/journal/<replaceable>machine-id</replaceable>/*.journal~</filename></term>
 211                                 <term><filename>/var/log/journal/<replaceable>machine-id</replaceable>/*.journal</filename></term>
 212                                 <term><filename>/var/log/journal/<replaceable>machine-id</replaceable>/*.journal~</filename></term>
 213
 214                                 <listitem><para><command>systemd-journald</command>
 215                                 writes entries to files in
 216                                 <filename>/run/log/journal/<replaceable>machine-id</replaceable>/</filename>
 217                                 or
 218                                 <filename>/var/log/journal/<replaceable>machine-id</replaceable>/</filename>
 219                                 with the <literal>.journal</literal>
 220                                 suffix. If the daemon is stopped
 221                                 uncleanly, or if the files are found
 222                                 to be corrupted, they are renamed
 223                                 using the <literal>.journal~</literal>
 224                                 suffix, and
 225                                 <command>systemd-journald</command>
 226                                 starts writing to a new
 227                                 file. <filename>/run</filename> is
 228                                 used when
 229                                 <filename>/var/log/journal</filename>
 230                                 is not available, or when
 231                                 <option>Storage=volatile</option> is
 232                                 set in the
 233                                 <citerefentry><refentrytitle>journald.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>
 234                                 configuration file.
 235                                 </para></listitem>
 236                         </varlistentry>
 237                 </variablelist>
 238         </refsect1>
 239
 240         <refsect1>
 241                 <title>See Also</title>
 242                 <para>
 243                         <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
 244                         <citerefentry><refentrytitle>journalctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
 245                         <citerefentry><refentrytitle>journald.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 246                         <citerefentry><refentrytitle>systemd.journal-fields</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
 247                         <citerefentry><refentrytitle>sd-journal</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 248                         <citerefentry><refentrytitle>setfacl</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
 249                         <command>pydoc systemd.journal</command>.
 250                 </para>
 251         </refsect1>
 252
 253 </refentry>