diff options
Diffstat (limited to '')
| -rw-r--r-- | man/systemd-journald.service.xml | 311 |
1 files changed, 311 insertions, 0 deletions
diff --git a/man/systemd-journald.service.xml b/man/systemd-journald.service.xml new file mode 100644 index 0000000..9167993 --- /dev/null +++ b/man/systemd-journald.service.xml @@ -0,0 +1,311 @@ +<?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"> + +<!-- + SPDX-License-Identifier: LGPL-2.1+ +--> + +<refentry id="systemd-journald.service"> + + <refentryinfo> + <title>systemd-journald.service</title> + <productname>systemd</productname> + </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 <filename>libc</filename> <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>3</manvolnum></citerefentry></para></listitem> + + <listitem><para>Standard output and standard error of service units. For further details see + below.</para></listitem> + + <listitem><para>Audit records, originating from the kernel 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. Individual fields making up a log record stored in the journal may be up to 2^64-1 bytes in size.</para> + + <para>The journal service stores log data either persistently below <filename>/var/log/journal</filename> or in a + volatile way below <filename>/run/log/journal/</filename> (in the latter case it is lost at reboot). By default, log + data is stored persistently if <filename>/var/log/journal/</filename> exists during boot, with an implicit fallback + to volatile storage otherwise. Use <varname>Storage=</varname> in + <citerefentry><refentrytitle>journald.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry> to configure + where log data is placed, independently of the existence of <filename>/var/log/journal/</filename>.</para> + + <para>On systems where <filename>/var/log/journal/</filename> does not exist yet but where persistent logging is + desired (and the default <filename>journald.conf</filename> is used), it is sufficient to create the directory, and + ensure it has the correct access modes and ownership:</para> + + <programlisting>mkdir -p /var/log/journal +systemd-tmpfiles --create --prefix /var/log/journal</programlisting> + + <para>See + <citerefentry><refentrytitle>journald.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry> + for information about the configuration of this service.</para> + </refsect1> + + <refsect1> + <title>Stream logging</title> + + <para>The systemd service manager invokes all service processes with standard output and standard error connected + to the journal by default. This behaviour may be altered via the + <varname>StandardOutput=</varname>/<varname>StandardError=</varname> unit file settings, see + <citerefentry><refentrytitle>systemd.exec</refentrytitle><manvolnum>5</manvolnum></citerefentry> for details. The + journal converts the log byte stream received this way into individual log records, splitting the stream at newline + (<literal>\n</literal>, ASCII <constant>10</constant>) and <constant>NUL</constant> bytes.</para> + + <para>If <filename>systemd-journald.service</filename> is stopped, the stream connections associated with all + services are terminated. Further writes to those streams by the service will result in <constant>EPIPE</constant> + errors. In order to react gracefully in this case it is recommended that programs logging to standard output/error + ignore such errors. If the <constant>SIGPIPE</constant> UNIX signal handler is not blocked or turned off, such + write attempts will also result in such process signals being generated, see + <citerefentry><refentrytitle>signal</refentrytitle><manvolnum>7</manvolnum></citerefentry>. To mitigate this issue, + systemd service manager explicitly turns off the <constant>SIGPIPE</constant> signal for all invoked processes by + default (this may be changed for each unit individually via the <varname>IgnoreSIGPIPE=</varname> option, see + <citerefentry><refentrytitle>systemd.exec</refentrytitle><manvolnum>5</manvolnum></citerefentry> for + details). After the standard output/standard error streams have been terminated they may not be recovered until the + services they are associated with are restarted. Note that during normal operation, + <filename>systemd-journald.service</filename> stores copies of the file descriptors for those streams in the + service manager. If <filename>systemd-journald.service</filename> is restarted using <command>systemctl + restart</command> or equivalent operation instead of a pair of separate <command>systemctl stop</command> and + <command>systemctl start</command> commands (or equivalent operations), these stream connections are not terminated + and survive the restart. It is thus safe to restart <filename>systemd-journald.service</filename>, but stopping it + is not recommended.</para> + + <para>Note that the log record metadata for records transferred via such standard output/error streams reflect the + metadata of the peer the stream was originally created for. If the stream connection is passed on to other + processes (such as further child processes forked off the main service process), the log records will not reflect + their metadata, but will continue to describe the original process. This is different from the other logging + transports listed above, which are inherently record based and where the metadata is always associated with the + individual record.</para> + + <para>In addition to the implicit standard output/error logging of services, stream logging is also available + via the <citerefentry><refentrytitle>systemd-cat</refentrytitle><manvolnum>1</manvolnum></citerefentry> command + line tool.</para> + + <para>Currently, the number of parallel log streams <filename>systemd-journald</filename> will accept is limited to + 4096. When this limit is reached further log streams may be established but will receive + <constant>EPIPE</constant> right from the beginning.</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 them to read + the journal files.</para> + + <para>By default, each logged in user will get their 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> + + <para>When <filename>systemd-journald</filename> ceases writing to a journal file, + it will be renamed to <literal><replaceable>original-name</replaceable>@<replaceable>suffix.journal</replaceable></literal> + (or <literal><replaceable>original-name</replaceable>@<replaceable>suffix.journal~</replaceable></literal>). + Such files are "archived" and will not be written to any more.</para> + + <para>In general, it is safe to read or copy any journal file (active or archived). + <citerefentry><refentrytitle>journalctl</refentrytitle><manvolnum>1</manvolnum></citerefentry> + and the functions in the + <citerefentry><refentrytitle>sd-journal</refentrytitle><manvolnum>3</manvolnum></citerefentry> + library should be able to read all entries that have been fully written.</para> + + <para><filename>systemd-journald</filename> will automatically remove the oldest + archived journal files to limit disk use. See <varname>SystemMaxUse=</varname> + and related settings in + <citerefentry><refentrytitle>journald.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>. + </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>3</manvolnum></citerefentry>, + <command>pydoc systemd.journal</command> + </para> + </refsect1> + +</refentry> |