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1604 lines
78 KiB
XML
1604 lines
78 KiB
XML
<?xml version='1.0'?>
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<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
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"http://www.oasis-open.org/docbook/xml/4.5/docbookx.dtd">
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<!-- SPDX-License-Identifier: LGPL-2.1-or-later -->
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<refentry id="systemd"
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xmlns:xi="http://www.w3.org/2001/XInclude">
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||
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<refentryinfo>
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||
<title>systemd</title>
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||
<productname>systemd</productname>
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||
</refentryinfo>
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||
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<refmeta>
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||
<refentrytitle>systemd</refentrytitle>
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<manvolnum>1</manvolnum>
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||
</refmeta>
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||
|
||
<refnamediv>
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<refname>systemd</refname>
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<refname>init</refname>
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<refpurpose>systemd system and service manager</refpurpose>
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||
</refnamediv>
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||
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<refsynopsisdiv>
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||
<cmdsynopsis>
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<command>/usr/lib/systemd/systemd</command>
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<arg choice="opt" rep="repeat">OPTIONS</arg>
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||
</cmdsynopsis>
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||
<cmdsynopsis>
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||
<command>init</command>
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||
<arg choice="opt" rep="repeat">OPTIONS</arg>
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||
<arg choice="req">COMMAND</arg>
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||
</cmdsynopsis>
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</refsynopsisdiv>
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||
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||
<refsect1>
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<title>Description</title>
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||
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<para>systemd is a system and service manager for Linux operating systems. When run as first process on
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boot (as PID 1), it acts as init system that brings up and maintains userspace services. Separate
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||
instances are started for logged-in users to start their services.</para>
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||
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||
<para><command>systemd</command> is usually not invoked directly by the user, but is installed as the
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||
<filename>/sbin/init</filename> symlink and started during early boot. The user manager instances are
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||
started automatically through the
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<citerefentry><refentrytitle>user@.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>
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||
service.</para>
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||
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||
<para>For compatibility with SysV, if the binary is called as <command>init</command> and is not the
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||
first process on the machine (PID is not 1), it will execute <command>telinit</command> and pass all
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||
command line arguments unmodified. That means <command>init</command> and <command>telinit</command> are
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||
mostly equivalent when invoked from normal login sessions. See
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||
<citerefentry><refentrytitle>telinit</refentrytitle><manvolnum>8</manvolnum></citerefentry> for more
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||
information.</para>
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||
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||
<para>When run as a system instance, systemd interprets the
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||
configuration file <filename>system.conf</filename> and the files
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||
in <filename>system.conf.d</filename> directories; when run as a
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||
user instance, systemd interprets the configuration file
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||
<filename>user.conf</filename> and the files in
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||
<filename>user.conf.d</filename> directories. See
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||
<citerefentry><refentrytitle>systemd-system.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>
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||
for more information.</para>
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||
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||
<para><command>systemd</command> contains native implementations of various tasks that need to be
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||
executed as part of the boot process. For example, it sets the hostname or configures the loopback
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||
network device. It also sets up and mounts various API file systems, such as <filename>/sys/</filename>,
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<filename>/proc/</filename>, and <filename>/dev/</filename>.</para>
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||
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<para><command>systemd</command> will also reset the system clock during early boot if it appears to be
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set incorrectly. See "System clock epoch" section below.</para>
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||
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||
<para>Note that some but not all interfaces provided by systemd are covered by the
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||
<ulink url="https://systemd.io/PORTABILITY_AND_STABILITY/">Interface Portability and Stability Promise</ulink>.</para>
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||
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||
<para>The D-Bus API of <command>systemd</command> is described in
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||
<citerefentry><refentrytitle>org.freedesktop.systemd1</refentrytitle><manvolnum>5</manvolnum></citerefentry>
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and
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<citerefentry><refentrytitle>org.freedesktop.LogControl1</refentrytitle><manvolnum>5</manvolnum></citerefentry>.
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||
</para>
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||
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||
<para>Systems which invoke systemd in a container or initrd environment should implement the <ulink
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||
url="https://systemd.io/CONTAINER_INTERFACE">Container Interface</ulink> or
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||
<ulink url="https://systemd.io/INITRD_INTERFACE/">initrd Interface</ulink>
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||
specifications, respectively.</para>
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||
</refsect1>
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||
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||
<refsect1>
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||
<title>Units</title>
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||
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||
<para>systemd provides a dependency system between various
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||
entities called "units" of 11 different types. Units encapsulate
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||
various objects that are relevant for system boot-up and
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||
maintenance. The majority of units are configured in unit
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||
configuration files, whose syntax and basic set of options is
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||
described in
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||
<citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
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||
however some are created automatically from other configuration
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||
files, dynamically from system state or programmatically at runtime.
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||
Units may be "active" (meaning started, bound, plugged in, …,
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||
depending on the unit type, see below), or "inactive" (meaning
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||
stopped, unbound, unplugged, …), as well as in the process of
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||
being activated or deactivated, i.e. between the two states (these
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||
states are called "activating", "deactivating"). A special
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||
"failed" state is available as well, which is very similar to
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||
"inactive" and is entered when the service failed in some way
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||
(process returned error code on exit, or crashed, an operation
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||
timed out, or after too many restarts). If this state is entered,
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||
the cause will be logged, for later reference. Note that the
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||
various unit types may have a number of additional substates,
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||
which are mapped to the five generalized unit states described
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||
here.</para>
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||
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||
<para>The following unit types are available:</para>
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||
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||
<orderedlist>
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||
<listitem><para>Service units, which start and control daemons
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||
and the processes they consist of. For details, see
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<citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
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||
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||
<listitem><para>Socket units, which encapsulate local IPC or
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||
network sockets in the system, useful for socket-based
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||
activation. For details about socket units, see
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||
<citerefentry><refentrytitle>systemd.socket</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
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||
for details on socket-based activation and other forms of
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||
activation, see
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||
<citerefentry><refentrytitle>daemon</refentrytitle><manvolnum>7</manvolnum></citerefentry>.</para></listitem>
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||
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||
<listitem><para>Target units are useful to group units, or
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||
provide well-known synchronization points during boot-up, see
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||
<citerefentry><refentrytitle>systemd.target</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
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||
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||
<listitem><para>Device units expose kernel devices in systemd
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||
and may be used to implement device-based activation. For
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||
details, see
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||
<citerefentry><refentrytitle>systemd.device</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
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||
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||
<listitem><para>Mount units control mount points in the file
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||
system, for details see
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||
<citerefentry><refentrytitle>systemd.mount</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
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||
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||
<listitem><para>Automount units provide automount capabilities,
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||
for on-demand mounting of file systems as well as parallelized
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||
boot-up. See
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||
<citerefentry><refentrytitle>systemd.automount</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
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||
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||
<listitem><para>Timer units are useful for triggering activation
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||
of other units based on timers. You may find details in
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||
<citerefentry><refentrytitle>systemd.timer</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
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||
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||
<listitem><para>Swap units are very similar to mount units and
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||
encapsulate memory swap partitions or files of the operating
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||
system. They are described in
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<citerefentry><refentrytitle>systemd.swap</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
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||
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||
<listitem><para>Path units may be used to activate other
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||
services when file system objects change or are modified. See
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||
<citerefentry><refentrytitle>systemd.path</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
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||
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||
<listitem><para>Slice units may be used to group units which
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||
manage system processes (such as service and scope units) in a
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||
hierarchical tree for resource management purposes. See
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||
<citerefentry><refentrytitle>systemd.slice</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
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||
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||
<listitem><para>Scope units are similar to service units, but
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||
manage foreign processes instead of starting them as well. See
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||
<citerefentry><refentrytitle>systemd.scope</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
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||
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||
</orderedlist>
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||
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||
<para>Units are named as their configuration files. Some units
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||
have special semantics. A detailed list is available in
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||
<citerefentry><refentrytitle>systemd.special</refentrytitle><manvolnum>7</manvolnum></citerefentry>.</para>
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||
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||
<para>systemd knows various kinds of dependencies, including
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||
positive and negative requirement dependencies (i.e.
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||
<varname>Requires=</varname> and <varname>Conflicts=</varname>) as
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||
well as ordering dependencies (<varname>After=</varname> and
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||
<varname>Before=</varname>). NB: ordering and requirement
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||
dependencies are orthogonal. If only a requirement dependency
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||
exists between two units (e.g. <filename>foo.service</filename>
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||
requires <filename>bar.service</filename>), but no ordering
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||
dependency (e.g. <filename>foo.service</filename> after
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||
<filename>bar.service</filename>) and both are requested to start,
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||
they will be started in parallel. It is a common pattern that both
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||
requirement and ordering dependencies are placed between two
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||
units. Also note that the majority of dependencies are implicitly
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||
created and maintained by systemd. In most cases, it should be
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||
unnecessary to declare additional dependencies manually, however
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||
it is possible to do this.</para>
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||
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||
<para>Application programs and units (via dependencies) may
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||
request state changes of units. In systemd, these requests are
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||
encapsulated as 'jobs' and maintained in a job queue. Jobs may
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||
succeed or can fail, their execution is ordered based on the
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||
ordering dependencies of the units they have been scheduled
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||
for.</para>
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||
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||
<para>On boot systemd activates the target unit
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||
<filename>default.target</filename> whose job is to activate
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||
on-boot services and other on-boot units by pulling them in via
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||
dependencies. Usually, the unit name is just an alias (symlink) for
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||
either <filename>graphical.target</filename> (for fully-featured
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||
boots into the UI) or <filename>multi-user.target</filename> (for
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||
limited console-only boots for use in embedded or server
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||
environments, or similar; a subset of graphical.target). However,
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||
it is at the discretion of the administrator to configure it as an
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||
alias to any other target unit. See
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<citerefentry><refentrytitle>systemd.special</refentrytitle><manvolnum>7</manvolnum></citerefentry>
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||
for details about these target units.</para>
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||
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||
<para>On first boot, <command>systemd</command> will enable or disable units according to preset policy.
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||
See <citerefentry><refentrytitle>systemd.preset</refentrytitle><manvolnum>5</manvolnum></citerefentry>
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||
and "First Boot Semantics" in
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<citerefentry><refentrytitle>machine-id</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para>
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||
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||
<para>systemd only keeps a minimal set of units loaded into memory. Specifically, the only units that are
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||
kept loaded into memory are those for which at least one of the following conditions is true:</para>
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||
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||
<orderedlist>
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||
<listitem><para>It is in an active, activating, deactivating or failed state (i.e. in any unit state except for <literal>inactive</literal>)</para></listitem>
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||
<listitem><para>It has a job queued for it</para></listitem>
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||
<listitem><para>It is a dependency of at least one other unit that is loaded into memory</para></listitem>
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||
<listitem><para>It has some form of resource still allocated (e.g. a service unit that is inactive but for which
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||
a process is still lingering that ignored the request to be terminated)</para></listitem>
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||
<listitem><para>It has been pinned into memory programmatically by a D-Bus call</para></listitem>
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||
</orderedlist>
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||
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||
<para>systemd will automatically and implicitly load units from disk — if they are not loaded yet — as soon as
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||
operations are requested for them. Thus, in many respects, the fact whether a unit is loaded or not is invisible to
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||
clients. Use <command>systemctl list-units --all</command> to comprehensively list all units currently loaded. Any
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||
unit for which none of the conditions above applies is promptly unloaded. Note that when a unit is unloaded from
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||
memory its accounting data is flushed out too. However, this data is generally not lost, as a journal log record
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||
is generated declaring the consumed resources whenever a unit shuts down.</para>
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||
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||
<para>Processes systemd spawns are placed in individual Linux control groups named after the unit which
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||
they belong to in the private systemd hierarchy. (see <ulink
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url="https://docs.kernel.org/admin-guide/cgroup-v2.html">Control Groups v2</ulink> for more information
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||
about control groups, or short "cgroups"). systemd uses this to effectively keep track of
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||
processes. Control group information is maintained in the kernel, and is accessible via the file system
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||
hierarchy (beneath <filename>/sys/fs/cgroup/</filename>), or in tools such as <citerefentry
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||
project='man-pages'><refentrytitle>systemd-cgls</refentrytitle><manvolnum>1</manvolnum></citerefentry> or
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||
<citerefentry
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||
project='man-pages'><refentrytitle>ps</refentrytitle><manvolnum>1</manvolnum></citerefentry> (<command>ps
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||
xawf -eo pid,user,cgroup,args</command> is particularly useful to list all processes and the systemd
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||
units they belong to.).</para>
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||
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||
<para>systemd is compatible with the SysV init system to a large
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||
degree: SysV init scripts are supported and simply read as an
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||
alternative (though limited) configuration file format. The SysV
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||
<filename>/dev/initctl</filename> interface is provided, and
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||
compatibility implementations of the various SysV client tools are
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||
available. In addition to that, various established Unix
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||
functionality such as <filename>/etc/fstab</filename> or the
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<filename>utmp</filename> database are supported.</para>
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||
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||
<para>systemd has a minimal transaction system: if a unit is
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||
requested to start up or shut down it will add it and all its
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dependencies to a temporary transaction. Then, it will verify if
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||
the transaction is consistent (i.e. whether the ordering of all
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||
units is cycle-free). If it is not, systemd will try to fix it up,
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||
and removes non-essential jobs from the transaction that might
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remove the loop. Also, systemd tries to suppress non-essential
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||
jobs in the transaction that would stop a running service. Finally
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||
it is checked whether the jobs of the transaction contradict jobs
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||
that have already been queued, and optionally the transaction is
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||
aborted then. If all worked out and the transaction is consistent
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||
and minimized in its impact it is merged with all already
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||
outstanding jobs and added to the run queue. Effectively this
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||
means that before executing a requested operation, systemd will
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verify that it makes sense, fixing it if possible, and only
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||
failing if it really cannot work.</para>
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||
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||
<para>Note that transactions are generated independently of a unit's
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||
state at runtime, hence, for example, if a start job is requested on an
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||
already started unit, it will still generate a transaction and wake up any
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||
inactive dependencies (and cause propagation of other jobs as per the
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||
defined relationships). This is because the enqueued job is at the time of
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||
execution compared to the target unit's state and is marked successful and
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||
complete when both satisfy. However, this job also pulls in other
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||
dependencies due to the defined relationships and thus leads to, in our
|
||
example, start jobs for any of those inactive units getting queued as
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||
well.</para>
|
||
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||
<para>Units may be generated dynamically at boot and system
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||
manager reload time, for example based on other configuration
|
||
files or parameters passed on the kernel command line. For details, see
|
||
<citerefentry><refentrytitle>systemd.generator</refentrytitle><manvolnum>7</manvolnum></citerefentry>.</para>
|
||
</refsect1>
|
||
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||
<refsect1>
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||
<title>Directories</title>
|
||
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||
<variablelist>
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||
<varlistentry>
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||
<term>System unit directories</term>
|
||
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||
<listitem><para>The systemd system manager reads unit
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||
configuration from various directories. Packages that want to
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||
install unit files shall place them in the directory returned
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||
by <command>pkg-config systemd
|
||
--variable=systemdsystemunitdir</command>. Other directories
|
||
checked are <filename>/usr/local/lib/systemd/system</filename>
|
||
and <filename>/usr/lib/systemd/system</filename>. User
|
||
configuration always takes precedence. <command>pkg-config
|
||
systemd --variable=systemdsystemconfdir</command> returns the
|
||
path of the system configuration directory. Packages should
|
||
alter the content of these directories only with the
|
||
<command>enable</command> and <command>disable</command>
|
||
commands of the
|
||
<citerefentry><refentrytitle>systemctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>
|
||
tool. Full list of directories is provided in
|
||
<citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>.
|
||
</para></listitem>
|
||
</varlistentry>
|
||
</variablelist>
|
||
|
||
<variablelist>
|
||
<varlistentry>
|
||
<term>User unit directories</term>
|
||
|
||
<listitem><para>Similar rules apply for the user unit
|
||
directories. However, here the
|
||
<ulink url="https://standards.freedesktop.org/basedir-spec/basedir-spec-latest.html">XDG
|
||
Base Directory specification</ulink> is followed to find
|
||
units. Applications should place their unit files in the
|
||
directory returned by <command>pkg-config systemd
|
||
--variable=systemduserunitdir</command>. Global configuration
|
||
is done in the directory reported by <command>pkg-config
|
||
systemd --variable=systemduserconfdir</command>. The
|
||
<command>enable</command> and <command>disable</command>
|
||
commands of the
|
||
<citerefentry><refentrytitle>systemctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>
|
||
tool can handle both global (i.e. for all users) and private
|
||
(for one user) enabling/disabling of units. Full list of
|
||
directories is provided in
|
||
<citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>.
|
||
</para></listitem>
|
||
</varlistentry>
|
||
</variablelist>
|
||
|
||
<variablelist>
|
||
<varlistentry>
|
||
<term>SysV init scripts directory</term>
|
||
|
||
<listitem><para>The location of the SysV init script directory
|
||
varies between distributions. If systemd cannot find a native
|
||
unit file for a requested service, it will look for a SysV
|
||
init script of the same name (with the
|
||
<filename>.service</filename> suffix
|
||
removed).</para></listitem>
|
||
</varlistentry>
|
||
</variablelist>
|
||
|
||
<variablelist>
|
||
<varlistentry>
|
||
<term>SysV runlevel link farm directory</term>
|
||
|
||
<listitem><para>The location of the SysV runlevel link farm
|
||
directory varies between distributions. systemd will take the
|
||
link farm into account when figuring out whether a service
|
||
shall be enabled. Note that a service unit with a native unit
|
||
configuration file cannot be started by activating it in the
|
||
SysV runlevel link farm.</para></listitem>
|
||
</varlistentry>
|
||
</variablelist>
|
||
</refsect1>
|
||
|
||
<refsect1>
|
||
<title>Signals</title>
|
||
|
||
<para>The service listens to various UNIX process signals that can be used to request various actions
|
||
asynchronously. The signal handling is enabled very early during boot, before any further processes are
|
||
invoked. However, a supervising container manager or similar that intends to request these operations via
|
||
this mechanism must take into consideration that this functionality is not available during the earliest
|
||
initialization phase. An <function>sd_notify()</function> notification message carrying the
|
||
<varname>X_SYSTEMD_SIGNALS_LEVEL=2</varname> field is emitted once the signal handlers are enabled, see
|
||
below. This may be used to schedule submission of these signals correctly.</para>
|
||
|
||
<variablelist>
|
||
<varlistentry>
|
||
<term><constant>SIGTERM</constant></term>
|
||
|
||
<listitem><para>Upon receiving this signal the systemd system
|
||
manager serializes its state, reexecutes itself and
|
||
deserializes the saved state again. This is mostly equivalent
|
||
to <command>systemctl daemon-reexec</command>.</para>
|
||
|
||
<para>systemd user managers will start the
|
||
<filename>exit.target</filename> unit when this signal is
|
||
received. This is mostly equivalent to <command>systemctl
|
||
--user start exit.target
|
||
--job-mode=replace-irreversibly</command>.</para></listitem>
|
||
</varlistentry>
|
||
|
||
<varlistentry>
|
||
<term><constant>SIGINT</constant></term>
|
||
|
||
<listitem><para>Upon receiving this signal the systemd system manager will start the
|
||
<filename>ctrl-alt-del.target</filename> unit. This is mostly equivalent to
|
||
<command>systemctl start ctrl-alt-del.target --job-mode=replace-irreversibly</command>. If
|
||
this signal is received more than 7 times per 2s, an immediate reboot is triggered. Note
|
||
that pressing
|
||
<keycombo><keycap>Ctrl</keycap><keycap>Alt</keycap><keycap>Del</keycap></keycombo> on the
|
||
console will trigger this signal. Hence, if a reboot is hanging, pressing
|
||
<keycombo><keycap>Ctrl</keycap><keycap>Alt</keycap><keycap>Del</keycap></keycombo> more than
|
||
7 times in 2 seconds is a relatively safe way to trigger an immediate reboot.</para>
|
||
|
||
<para>systemd user managers treat this signal the same way as
|
||
<constant>SIGTERM</constant>.</para></listitem>
|
||
</varlistentry>
|
||
|
||
<varlistentry>
|
||
<term><constant>SIGWINCH</constant></term>
|
||
|
||
<listitem><para>When this signal is received the systemd
|
||
system manager will start the
|
||
<filename>kbrequest.target</filename> unit. This is mostly
|
||
equivalent to <command>systemctl start
|
||
kbrequest.target</command>.</para>
|
||
|
||
<para>This signal is ignored by systemd user
|
||
managers.</para></listitem>
|
||
</varlistentry>
|
||
|
||
<varlistentry>
|
||
<term><constant>SIGPWR</constant></term>
|
||
|
||
<listitem><para>When this signal is received the systemd
|
||
manager will start the <filename>sigpwr.target</filename>
|
||
unit. This is mostly equivalent to <command>systemctl start
|
||
sigpwr.target</command>.</para></listitem>
|
||
</varlistentry>
|
||
|
||
<varlistentry>
|
||
<term><constant>SIGUSR1</constant></term>
|
||
|
||
<listitem><para>When this signal is received the systemd
|
||
manager will try to reconnect to the D-Bus
|
||
bus.</para></listitem>
|
||
</varlistentry>
|
||
|
||
<varlistentry>
|
||
<term><constant>SIGUSR2</constant></term>
|
||
|
||
<listitem><para>When this signal is received the systemd
|
||
manager will log its complete state in human-readable form.
|
||
The data logged is the same as printed by
|
||
<command>systemd-analyze dump</command>.</para></listitem>
|
||
</varlistentry>
|
||
|
||
<varlistentry>
|
||
<term><constant>SIGHUP</constant></term>
|
||
|
||
<listitem><para>Reloads the complete daemon configuration.
|
||
This is mostly equivalent to <command>systemctl
|
||
daemon-reload</command>.</para></listitem>
|
||
</varlistentry>
|
||
|
||
<varlistentry>
|
||
<term><constant>SIGRTMIN+0</constant></term>
|
||
|
||
<listitem><para>Enters default mode, starts the
|
||
<filename>default.target</filename> unit. This is mostly
|
||
equivalent to <command>systemctl isolate
|
||
default.target</command>.</para></listitem>
|
||
</varlistentry>
|
||
|
||
<varlistentry>
|
||
<term><constant>SIGRTMIN+1</constant></term>
|
||
|
||
<listitem><para>Enters rescue mode, starts the
|
||
<filename>rescue.target</filename> unit. This is mostly
|
||
equivalent to <command>systemctl isolate
|
||
rescue.target</command>.</para></listitem>
|
||
</varlistentry>
|
||
|
||
<varlistentry>
|
||
<term><constant>SIGRTMIN+2</constant></term>
|
||
|
||
<listitem><para>Enters emergency mode, starts the
|
||
<filename>emergency.service</filename> unit. This is mostly
|
||
equivalent to <command>systemctl isolate
|
||
emergency.service</command>.</para></listitem>
|
||
</varlistentry>
|
||
|
||
<varlistentry>
|
||
<term><constant>SIGRTMIN+3</constant></term>
|
||
|
||
<listitem><para>Halts the machine, starts the
|
||
<filename>halt.target</filename> unit. This is mostly
|
||
equivalent to <command>systemctl start halt.target
|
||
--job-mode=replace-irreversibly</command>.</para>
|
||
</listitem>
|
||
</varlistentry>
|
||
|
||
<varlistentry>
|
||
<term><constant>SIGRTMIN+4</constant></term>
|
||
|
||
<listitem><para>Powers off the machine, starts the
|
||
<filename>poweroff.target</filename> unit. This is mostly
|
||
equivalent to <command>systemctl start poweroff.target
|
||
--job-mode=replace-irreversibly</command>.</para>
|
||
</listitem>
|
||
</varlistentry>
|
||
|
||
<varlistentry>
|
||
<term><constant>SIGRTMIN+5</constant></term>
|
||
|
||
<listitem><para>Reboots the machine, starts the
|
||
<filename>reboot.target</filename> unit. This is mostly
|
||
equivalent to <command>systemctl start reboot.target
|
||
--job-mode=replace-irreversibly</command>.</para>
|
||
</listitem>
|
||
</varlistentry>
|
||
|
||
<varlistentry>
|
||
<term><constant>SIGRTMIN+6</constant></term>
|
||
|
||
<listitem><para>Reboots the machine via kexec, starts the
|
||
<filename>kexec.target</filename> unit. This is mostly
|
||
equivalent to <command>systemctl start kexec.target
|
||
--job-mode=replace-irreversibly</command>.</para>
|
||
</listitem>
|
||
</varlistentry>
|
||
|
||
<varlistentry>
|
||
<term><constant>SIGRTMIN+7</constant></term>
|
||
|
||
<listitem><para>Reboots userspace, starts the <filename>soft-reboot.target</filename> unit. This is
|
||
mostly equivalent to <command>systemctl start soft-reboot.target
|
||
--job-mode=replace-irreversibly</command>.</para>
|
||
|
||
<xi:include href="version-info.xml" xpointer="v254"/>
|
||
</listitem>
|
||
</varlistentry>
|
||
|
||
<varlistentry>
|
||
<term><constant>SIGRTMIN+13</constant></term>
|
||
|
||
<listitem><para>Immediately halts the machine.</para></listitem>
|
||
</varlistentry>
|
||
|
||
<varlistentry>
|
||
<term><constant>SIGRTMIN+14</constant></term>
|
||
|
||
<listitem><para>Immediately powers off the machine.</para></listitem>
|
||
</varlistentry>
|
||
|
||
<varlistentry>
|
||
<term><constant>SIGRTMIN+15</constant></term>
|
||
|
||
<listitem><para>Immediately reboots the machine.</para></listitem>
|
||
</varlistentry>
|
||
|
||
<varlistentry>
|
||
<term><constant>SIGRTMIN+16</constant></term>
|
||
|
||
<listitem><para>Immediately reboots the machine with kexec.</para></listitem>
|
||
</varlistentry>
|
||
|
||
<varlistentry>
|
||
<term><constant>SIGRTMIN+17</constant></term>
|
||
|
||
<listitem><para>Immediately reboots the userspace.</para>
|
||
|
||
<xi:include href="version-info.xml" xpointer="v254"/></listitem>
|
||
</varlistentry>
|
||
|
||
<varlistentry>
|
||
<term><constant>SIGRTMIN+20</constant></term>
|
||
|
||
<listitem><para>Enables display of status messages on the
|
||
console, as controlled via
|
||
<varname>systemd.show_status=1</varname> on the kernel command
|
||
line.</para></listitem>
|
||
</varlistentry>
|
||
|
||
<varlistentry>
|
||
<term><constant>SIGRTMIN+21</constant></term>
|
||
|
||
<listitem><para>Disables display of
|
||
status messages on the console, as
|
||
controlled via
|
||
<varname>systemd.show_status=0</varname>
|
||
on the kernel command
|
||
line.</para></listitem>
|
||
</varlistentry>
|
||
|
||
<varlistentry>
|
||
<term><constant>SIGRTMIN+22</constant></term>
|
||
|
||
<listitem><para>Sets the service manager's log level to <literal>debug</literal>, in a fashion equivalent to
|
||
<varname>systemd.log_level=debug</varname> on the kernel command line.</para></listitem>
|
||
</varlistentry>
|
||
|
||
<varlistentry>
|
||
<term><constant>SIGRTMIN+23</constant></term>
|
||
|
||
<listitem><para>Restores the log level to its configured value. The configured value is derived from – in order
|
||
of priority – the value specified with <varname>systemd.log-level=</varname> on the kernel command line, or the
|
||
value specified with <option>LogLevel=</option> in the configuration file, or the built-in default of
|
||
<literal>info</literal>.</para>
|
||
|
||
<xi:include href="version-info.xml" xpointer="v239"/></listitem>
|
||
</varlistentry>
|
||
|
||
<varlistentry>
|
||
<term><constant>SIGRTMIN+24</constant></term>
|
||
|
||
<listitem><para>Immediately exits the manager (only available
|
||
for --user instances).</para>
|
||
|
||
<xi:include href="version-info.xml" xpointer="v195"/></listitem>
|
||
</varlistentry>
|
||
|
||
<varlistentry>
|
||
<term><constant>SIGRTMIN+25</constant></term>
|
||
|
||
<listitem><para>Upon receiving this signal the systemd manager will reexecute itself. This
|
||
is mostly equivalent to <command>systemctl daemon-reexec</command> except that it will be
|
||
done asynchronously.</para>
|
||
|
||
<para>The systemd system manager treats this signal the same way as
|
||
<constant>SIGTERM</constant>.</para>
|
||
|
||
<xi:include href="version-info.xml" xpointer="v250"/></listitem>
|
||
</varlistentry>
|
||
|
||
<varlistentry>
|
||
<term><constant>SIGRTMIN+26</constant></term>
|
||
|
||
<listitem><para>Restores the log target to its configured value. The configured value is derived from – in
|
||
order of priority – the value specified with <varname>systemd.log-target=</varname> on the kernel command line,
|
||
or the value specified with <option>LogTarget=</option> in the configuration file, or the built-in
|
||
default.</para>
|
||
|
||
<xi:include href="version-info.xml" xpointer="v239"/></listitem>
|
||
</varlistentry>
|
||
|
||
<varlistentry>
|
||
<term><constant>SIGRTMIN+27</constant></term>
|
||
<term><constant>SIGRTMIN+28</constant></term>
|
||
|
||
<listitem><para>Sets the log target to <literal>console</literal> on <constant>SIGRTMIN+27</constant> (or
|
||
<literal>kmsg</literal> on <constant>SIGRTMIN+28</constant>), in a fashion equivalent to
|
||
<varname>systemd.log_target=console</varname> (or <varname>systemd.log_target=kmsg</varname> on
|
||
<constant>SIGRTMIN+28</constant>) on the kernel command line.</para>
|
||
|
||
<xi:include href="version-info.xml" xpointer="v239"/></listitem>
|
||
</varlistentry>
|
||
</variablelist>
|
||
</refsect1>
|
||
|
||
<refsect1>
|
||
<title>Environment</title>
|
||
|
||
<para>The environment block for the system manager is initially set by the kernel. (In particular,
|
||
<literal>key=value</literal> assignments on the kernel command line are turned into environment
|
||
variables for PID 1). For the user manager, the system manager sets the environment as described in the
|
||
"Environment Variables in Spawned Processes" section of
|
||
<citerefentry><refentrytitle>systemd.exec</refentrytitle><manvolnum>5</manvolnum></citerefentry>. The
|
||
<varname>DefaultEnvironment=</varname> setting in the system manager applies to all services including
|
||
<filename>user@.service</filename>. Additional entries may be configured (as for any other service)
|
||
through the <varname>Environment=</varname> and <varname>EnvironmentFile=</varname> settings for
|
||
<filename>user@.service</filename> (see
|
||
<citerefentry><refentrytitle>systemd.exec</refentrytitle><manvolnum>5</manvolnum></citerefentry>). Also,
|
||
additional environment variables may be set through the <varname>ManagerEnvironment=</varname> setting in
|
||
<citerefentry><refentrytitle>systemd-system.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>
|
||
and
|
||
<citerefentry><refentrytitle>systemd-user.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>.
|
||
</para>
|
||
|
||
<para>Some of the variables understood by <command>systemd</command>:</para>
|
||
|
||
<variablelist class='environment-variables'>
|
||
<varlistentry>
|
||
<term><varname>$SYSTEMD_LOG_LEVEL</varname></term>
|
||
<listitem><xi:include href="common-variables.xml" xpointer="log-level-body" />
|
||
|
||
<para>This can be overridden with <option>--log-level=</option>.</para></listitem>
|
||
</varlistentry>
|
||
|
||
<varlistentry>
|
||
<term><varname>$SYSTEMD_LOG_COLOR</varname></term>
|
||
<listitem><xi:include href="common-variables.xml" xpointer="log-color-body" />
|
||
|
||
<para>This can be overridden with <option>--log-color=</option>.</para></listitem>
|
||
</varlistentry>
|
||
|
||
<varlistentry>
|
||
<term><varname>$SYSTEMD_LOG_TIME</varname></term>
|
||
<listitem><xi:include href="common-variables.xml" xpointer="log-time-body" />
|
||
|
||
<para>This can be overridden with <option>--log-time=</option>.</para>
|
||
|
||
<xi:include href="version-info.xml" xpointer="v246"/></listitem>
|
||
</varlistentry>
|
||
|
||
<varlistentry>
|
||
<term><varname>$SYSTEMD_LOG_LOCATION</varname></term>
|
||
<listitem><xi:include href="common-variables.xml" xpointer="log-location-body" />
|
||
|
||
<para>This can be overridden with <option>--log-location=</option>.</para></listitem>
|
||
</varlistentry>
|
||
|
||
<varlistentry>
|
||
<term><varname>$SYSTEMD_LOG_TID</varname></term>
|
||
<listitem><xi:include href="common-variables.xml" xpointer="log-tid-body" />
|
||
|
||
<xi:include href="version-info.xml" xpointer="v247"/></listitem>
|
||
</varlistentry>
|
||
|
||
<varlistentry>
|
||
<term><varname>$SYSTEMD_LOG_TARGET</varname></term>
|
||
<listitem><xi:include href="common-variables.xml" xpointer="log-target-body" />
|
||
|
||
<para>This can be overridden with <option>--log-target=</option>.</para></listitem>
|
||
</varlistentry>
|
||
|
||
<varlistentry>
|
||
<term><varname>$SYSTEMD_LOG_RATELIMIT_KMSG</varname></term>
|
||
<listitem><xi:include href="common-variables.xml" xpointer="log-ratelimit-kmsg-body" />
|
||
|
||
<xi:include href="version-info.xml" xpointer="v254"/></listitem>
|
||
</varlistentry>
|
||
|
||
<varlistentry>
|
||
<term><varname>$XDG_CONFIG_HOME</varname></term>
|
||
<term><varname>$XDG_CONFIG_DIRS</varname></term>
|
||
<term><varname>$XDG_DATA_HOME</varname></term>
|
||
<term><varname>$XDG_DATA_DIRS</varname></term>
|
||
|
||
<listitem><para>The systemd user manager uses these variables
|
||
in accordance to the <ulink
|
||
url="https://standards.freedesktop.org/basedir-spec/basedir-spec-latest.html">XDG
|
||
Base Directory specification</ulink> to find its
|
||
configuration.</para></listitem>
|
||
</varlistentry>
|
||
|
||
<varlistentry>
|
||
<term><varname>$SYSTEMD_UNIT_PATH</varname></term>
|
||
<term><varname>$SYSTEMD_GENERATOR_PATH</varname></term>
|
||
<term><varname>$SYSTEMD_ENVIRONMENT_GENERATOR_PATH</varname></term>
|
||
|
||
<listitem><para>Controls where systemd looks for unit files and
|
||
generators.</para>
|
||
<para>These variables may contain a list of paths, separated by colons
|
||
(<literal>:</literal>). When set, if the list ends with an empty
|
||
component (<literal>...:</literal>), this list is prepended to the
|
||
usual set of paths. Otherwise, the specified list replaces the usual
|
||
set of paths.
|
||
</para></listitem>
|
||
</varlistentry>
|
||
|
||
<xi:include href="common-variables.xml" xpointer="pager"/>
|
||
<xi:include href="common-variables.xml" xpointer="less"/>
|
||
<xi:include href="common-variables.xml" xpointer="lesscharset"/>
|
||
<xi:include href="common-variables.xml" xpointer="lesssecure"/>
|
||
<xi:include href="common-variables.xml" xpointer="colors"/>
|
||
<xi:include href="common-variables.xml" xpointer="urlify"/>
|
||
|
||
<varlistentry>
|
||
<term><varname>$LISTEN_PID</varname></term>
|
||
<term><varname>$LISTEN_FDS</varname></term>
|
||
<term><varname>$LISTEN_FDNAMES</varname></term>
|
||
|
||
<listitem><para>Set by systemd for supervised processes during
|
||
socket-based activation. See
|
||
<citerefentry><refentrytitle>sd_listen_fds</refentrytitle><manvolnum>3</manvolnum></citerefentry>
|
||
for more information.</para></listitem>
|
||
</varlistentry>
|
||
|
||
<varlistentry>
|
||
<term><varname>$NOTIFY_SOCKET</varname></term>
|
||
|
||
<listitem><para>Set by service manager for its services for status and readiness notifications. Also
|
||
consumed by service manager for notifying supervising container managers or service managers up the
|
||
stack about its own progress. See
|
||
<citerefentry><refentrytitle>sd_notify</refentrytitle><manvolnum>3</manvolnum></citerefentry> and the
|
||
relevant section below for more information.</para></listitem>
|
||
</varlistentry>
|
||
</variablelist>
|
||
|
||
<para>For further environment variables understood by systemd and its various components, see <ulink
|
||
url="https://systemd.io/ENVIRONMENT">Known Environment Variables</ulink>.</para>
|
||
</refsect1>
|
||
|
||
<refsect1>
|
||
<title>Kernel Command Line</title>
|
||
|
||
<para>When run as the system instance, systemd parses a number of options listed below. They can be
|
||
specified as kernel command line arguments which are parsed from a number of sources depending on the
|
||
environment in which systemd is executed. If run inside a Linux container, these options are parsed from
|
||
the command line arguments passed to systemd itself, next to any of the command line options listed in
|
||
the Options section above. If run outside of Linux containers, these arguments are parsed from
|
||
<filename>/proc/cmdline</filename> and from the <literal>SystemdOptions</literal> EFI variable
|
||
(on EFI systems) instead. Options from <filename>/proc/cmdline</filename> have higher priority.</para>
|
||
|
||
<para>Note: use of <literal>SystemdOptions</literal> is deprecated.</para>
|
||
|
||
<para>The following variables are understood:</para>
|
||
|
||
<variablelist class='kernel-commandline-options'>
|
||
<varlistentry>
|
||
<term><varname>systemd.unit=</varname></term>
|
||
<term><varname>rd.systemd.unit=</varname></term>
|
||
|
||
<listitem><para>Overrides the unit to activate on boot. Defaults to
|
||
<filename>default.target</filename>. This may be used to temporarily boot into a different boot unit,
|
||
for example <filename>rescue.target</filename> or <filename>emergency.service</filename>. See
|
||
<citerefentry><refentrytitle>systemd.special</refentrytitle><manvolnum>7</manvolnum></citerefentry>
|
||
for details about these units. The option prefixed with <literal>rd.</literal> is honored only in the
|
||
initrd, while the one that is not prefixed only in the main system.</para></listitem>
|
||
</varlistentry>
|
||
|
||
<varlistentry>
|
||
<term><varname>systemd.dump_core</varname></term>
|
||
|
||
<listitem><para>Takes a boolean argument or enables the option if specified
|
||
without an argument. If enabled, the systemd manager (PID 1) dumps core when
|
||
it crashes. Otherwise, no core dump is created. Defaults to enabled.</para>
|
||
|
||
<xi:include href="version-info.xml" xpointer="v233"/>
|
||
</listitem>
|
||
</varlistentry>
|
||
|
||
<varlistentry>
|
||
<term><varname>systemd.crash_chvt</varname></term>
|
||
|
||
<listitem><para>Takes a positive integer, or a boolean argument. Can be also specified without an
|
||
argument, with the same effect as a positive boolean. If a positive integer (in the range 1–63) is
|
||
specified, the system manager (PID 1) will activate the specified virtual terminal when it crashes.
|
||
Defaults to disabled, meaning that no such switch is attempted. If set to enabled, the virtual
|
||
terminal the kernel messages are written to is used instead.</para>
|
||
|
||
<xi:include href="version-info.xml" xpointer="v233"/></listitem>
|
||
</varlistentry>
|
||
|
||
<varlistentry>
|
||
<term><varname>systemd.crash_shell</varname></term>
|
||
|
||
<listitem><para>Takes a boolean argument or enables the option if specified
|
||
without an argument. If enabled, the system manager (PID 1) spawns a shell
|
||
when it crashes. Otherwise, no shell is spawned. Defaults to disabled, for
|
||
security reasons, as the shell is not protected by password authentication.</para>
|
||
|
||
<xi:include href="version-info.xml" xpointer="v233"/></listitem>
|
||
</varlistentry>
|
||
|
||
<varlistentry>
|
||
<term><varname>systemd.crash_action=</varname></term>
|
||
|
||
<listitem><para>Takes one of <literal>freeze</literal>, <literal>reboot</literal> or
|
||
<literal>poweroff</literal>. Defaults to <literal>freeze</literal>. If set to
|
||
<literal>freeze</literal>, the system will hang indefinitely when the system manager (PID 1) crashes.
|
||
If set to <literal>reboot</literal>, the system manager (PID 1) will reboot the machine automatically
|
||
when it crashes, after a 10s delay. If set to <literal>poweroff</literal>, the system manager (PID 1)
|
||
will power off the machine immediately when it crashes. If combined with
|
||
<varname>systemd.crash_shell</varname>, the configured crash action is executed after the shell
|
||
exits.</para>
|
||
|
||
<xi:include href="version-info.xml" xpointer="v256"/></listitem>
|
||
</varlistentry>
|
||
|
||
<varlistentry>
|
||
<term><varname>systemd.confirm_spawn</varname></term>
|
||
|
||
<listitem><para>Takes a boolean argument or a path to the virtual console
|
||
where the confirmation messages should be emitted. Can be also specified
|
||
without an argument, with the same effect as a positive boolean. If enabled,
|
||
the system manager (PID 1) asks for confirmation when spawning processes
|
||
using <option>/dev/console</option>. If a path or a console name (such as
|
||
<literal>ttyS0</literal>) is provided, the virtual console pointed to by this
|
||
path or described by the give name will be used instead. Defaults to disabled.
|
||
</para>
|
||
|
||
<xi:include href="version-info.xml" xpointer="v233"/></listitem>
|
||
</varlistentry>
|
||
|
||
<varlistentry>
|
||
<term><varname>systemd.service_watchdogs=</varname></term>
|
||
|
||
<listitem><para>Takes a boolean argument. If disabled, all service runtime
|
||
watchdogs (<option>WatchdogSec=</option>) and emergency actions (e.g.
|
||
<option>OnFailure=</option> or <option>StartLimitAction=</option>) are
|
||
ignored by the system manager (PID 1); see
|
||
<citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>.
|
||
Defaults to enabled, i.e. watchdogs and failure actions are processed
|
||
normally. The hardware watchdog is not affected by this
|
||
option.</para>
|
||
|
||
<xi:include href="version-info.xml" xpointer="v237"/></listitem>
|
||
</varlistentry>
|
||
|
||
<varlistentry>
|
||
<term><varname>systemd.show_status</varname></term>
|
||
|
||
<listitem><para>Takes a boolean argument or the constants <constant>error</constant> and
|
||
<constant>auto</constant>. Can be also specified without an argument, with the same effect as a
|
||
positive boolean. If enabled, the systemd manager (PID 1) shows terse service status updates on the
|
||
console during bootup. With <constant>error</constant>, only messages about failures are shown, but
|
||
boot is otherwise quiet. <constant>auto</constant> behaves like <option>false</option> until there is
|
||
a significant delay in boot. Defaults to enabled, unless <option>quiet</option> is passed as kernel
|
||
command line option, in which case it defaults to <constant>error</constant>. If specified overrides
|
||
the system manager configuration file option <option>ShowStatus=</option>, see
|
||
<citerefentry><refentrytitle>systemd-system.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>.
|
||
</para>
|
||
|
||
<xi:include href="version-info.xml" xpointer="v233"/></listitem>
|
||
</varlistentry>
|
||
|
||
<varlistentry>
|
||
<term><varname>systemd.status_unit_format=</varname></term>
|
||
|
||
<listitem><para>Takes <option>name</option>, <option>description</option> or
|
||
<option>combined</option> as the value. If <option>name</option>, the system manager will use unit
|
||
names in status messages. If <option>combined</option>, the system manager will use unit names and
|
||
description in status messages. When specified, overrides the system manager configuration file
|
||
option <option>StatusUnitFormat=</option>, see
|
||
<citerefentry><refentrytitle>systemd-system.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>.
|
||
</para>
|
||
|
||
<xi:include href="version-info.xml" xpointer="v243"/></listitem>
|
||
</varlistentry>
|
||
|
||
<varlistentry>
|
||
<term><varname>systemd.log_color</varname></term>
|
||
<term><varname>systemd.log_level=</varname></term>
|
||
<term><varname>systemd.log_location</varname></term>
|
||
<term><varname>systemd.log_target=</varname></term>
|
||
<term><varname>systemd.log_time</varname></term>
|
||
<term><varname>systemd.log_tid</varname></term>
|
||
<term><varname>systemd.log_ratelimit_kmsg</varname></term>
|
||
|
||
<listitem><para>Controls log output, with the same effect as the
|
||
<varname>$SYSTEMD_LOG_COLOR</varname>, <varname>$SYSTEMD_LOG_LEVEL</varname>,
|
||
<varname>$SYSTEMD_LOG_LOCATION</varname>, <varname>$SYSTEMD_LOG_TARGET</varname>,
|
||
<varname>$SYSTEMD_LOG_TIME</varname>, <varname>$SYSTEMD_LOG_TID</varname> and
|
||
<varname>$SYSTEMD_LOG_RATELIMIT_KMSG</varname> environment variables described above.
|
||
<varname>systemd.log_color</varname>, <varname>systemd.log_location</varname>,
|
||
<varname>systemd.log_time</varname>, <varname>systemd.log_tid</varname> and
|
||
<varname>systemd.log_ratelimit_kmsg</varname> can be specified without
|
||
an argument, with the same effect as a positive boolean.</para></listitem>
|
||
</varlistentry>
|
||
|
||
<varlistentry>
|
||
<term><varname>systemd.default_standard_output=</varname></term>
|
||
<term><varname>systemd.default_standard_error=</varname></term>
|
||
|
||
<listitem><para>Controls default standard output and error output for services and sockets. That is,
|
||
controls the default for <option>StandardOutput=</option> and <option>StandardError=</option> (see
|
||
<citerefentry><refentrytitle>systemd.exec</refentrytitle><manvolnum>5</manvolnum></citerefentry> for
|
||
details). Takes one of <option>inherit</option>, <option>null</option>, <option>tty</option>,
|
||
<option>journal</option>, <option>journal+console</option>, <option>kmsg</option>,
|
||
<option>kmsg+console</option>. If the argument is omitted
|
||
<varname>systemd.default-standard-output=</varname> defaults to <option>journal</option> and
|
||
<varname>systemd.default-standard-error=</varname> to <option>inherit</option>.</para></listitem>
|
||
</varlistentry>
|
||
|
||
<varlistentry>
|
||
<term><varname>systemd.setenv=</varname></term>
|
||
|
||
<listitem><para>Takes a string argument in the form
|
||
VARIABLE=VALUE. May be used to set default environment
|
||
variables to add to forked child processes. May be used more
|
||
than once to set multiple variables.</para></listitem>
|
||
</varlistentry>
|
||
|
||
<varlistentry>
|
||
<term><varname>systemd.machine_id=</varname></term>
|
||
|
||
<listitem><para>Takes a 32 character hex value to be
|
||
used for setting the machine-id. Intended mostly for
|
||
network booting where the same machine-id is desired
|
||
for every boot.</para>
|
||
|
||
<xi:include href="version-info.xml" xpointer="v229"/></listitem>
|
||
</varlistentry>
|
||
|
||
<varlistentry>
|
||
<term><varname>systemd.set_credential=</varname></term>
|
||
<term><varname>systemd.set_credential_binary=</varname></term>
|
||
|
||
<listitem><para>Sets a system credential, which can then be propagated to system services using the
|
||
<varname>ImportCredential=</varname> or <varname>LoadCredential=</varname> setting, see
|
||
<citerefentry><refentrytitle>systemd.exec</refentrytitle><manvolnum>5</manvolnum></citerefentry> for
|
||
details. Takes a pair of credential name and value, separated by a colon. The
|
||
<varname>systemd.set_credential=</varname> parameter expects the credential value in literal text
|
||
form, the <varname>systemd.set_credential_binary=</varname> parameter takes binary data encoded in
|
||
Base64. Note that the kernel command line is typically accessible by unprivileged programs in
|
||
<filename>/proc/cmdline</filename>. Thus, this mechanism is not suitable for transferring sensitive
|
||
data. Use it only for data that is not sensitive (e.g. public keys/certificates, rather than private
|
||
keys), or in testing/debugging environments.</para>
|
||
|
||
<para>For further information see <ulink url="https://systemd.io/CREDENTIALS">System and Service
|
||
Credentials</ulink> documentation.</para>
|
||
|
||
<xi:include href="version-info.xml" xpointer="v251"/></listitem>
|
||
</varlistentry>
|
||
|
||
<varlistentry>
|
||
<term><varname>systemd.import_credentials=</varname></term>
|
||
|
||
<listitem><para>Takes a boolean argument. If false disables importing credentials from the kernel
|
||
command line, the DMI/SMBIOS OEM string table, the qemu_fw_cfg subsystem or the EFI kernel
|
||
stub.</para>
|
||
|
||
<xi:include href="version-info.xml" xpointer="v251"/></listitem>
|
||
</varlistentry>
|
||
|
||
<varlistentry>
|
||
<term><varname>quiet</varname></term>
|
||
|
||
<listitem><para>Turn off status output at boot, much like
|
||
<varname>systemd.show_status=no</varname> would. Note that
|
||
this option is also read by the kernel itself and disables
|
||
kernel log output. Passing this option hence turns off the
|
||
usual output from both the system manager and the kernel.
|
||
</para>
|
||
|
||
<xi:include href="version-info.xml" xpointer="v186"/></listitem>
|
||
</varlistentry>
|
||
|
||
<varlistentry>
|
||
<term><varname>debug</varname></term>
|
||
|
||
<listitem><para>Turn on debugging output. This is equivalent
|
||
to <varname>systemd.log_level=debug</varname>. Note that this
|
||
option is also read by the kernel itself and enables kernel
|
||
debug output. Passing this option hence turns on the debug
|
||
output from both the system manager and the
|
||
kernel.</para>
|
||
|
||
<xi:include href="version-info.xml" xpointer="v205"/></listitem>
|
||
</varlistentry>
|
||
|
||
<varlistentry>
|
||
<term><varname>emergency</varname></term>
|
||
<term><varname>rd.emergency</varname></term>
|
||
<term><varname>-b</varname></term>
|
||
|
||
<listitem><para>Boot into emergency mode. This is equivalent
|
||
to <varname>systemd.unit=emergency.target</varname> or
|
||
<varname>rd.systemd.unit=emergency.target</varname>, respectively, and
|
||
provided for compatibility reasons and to be easier to type.</para>
|
||
|
||
<xi:include href="version-info.xml" xpointer="v186"/></listitem>
|
||
</varlistentry>
|
||
|
||
<varlistentry>
|
||
<term><varname>rescue</varname></term>
|
||
<term><varname>rd.rescue</varname></term>
|
||
<term><varname>single</varname></term>
|
||
<term><varname>s</varname></term>
|
||
<term><varname>S</varname></term>
|
||
<term><varname>1</varname></term>
|
||
|
||
<listitem><para>Boot into rescue mode. This is equivalent to
|
||
<varname>systemd.unit=rescue.target</varname> or
|
||
<varname>rd.systemd.unit=rescue.target</varname>, respectively, and
|
||
provided for compatibility reasons and to be easier to type.</para>
|
||
|
||
<xi:include href="version-info.xml" xpointer="v186"/></listitem>
|
||
</varlistentry>
|
||
|
||
<varlistentry>
|
||
<term><varname>2</varname></term>
|
||
<term><varname>3</varname></term>
|
||
<term><varname>4</varname></term>
|
||
<term><varname>5</varname></term>
|
||
|
||
<listitem><para>Boot into the specified legacy SysV runlevel.
|
||
These are equivalent to
|
||
<varname>systemd.unit=runlevel2.target</varname>,
|
||
<varname>systemd.unit=runlevel3.target</varname>,
|
||
<varname>systemd.unit=runlevel4.target</varname>, and
|
||
<varname>systemd.unit=runlevel5.target</varname>,
|
||
respectively, and provided for compatibility reasons and to be
|
||
easier to type.</para>
|
||
|
||
<xi:include href="version-info.xml" xpointer="v186"/></listitem>
|
||
</varlistentry>
|
||
|
||
<varlistentry>
|
||
<term><varname>locale.LANG=</varname></term>
|
||
<term><varname>locale.LANGUAGE=</varname></term>
|
||
<term><varname>locale.LC_CTYPE=</varname></term>
|
||
<term><varname>locale.LC_NUMERIC=</varname></term>
|
||
<term><varname>locale.LC_TIME=</varname></term>
|
||
<term><varname>locale.LC_COLLATE=</varname></term>
|
||
<term><varname>locale.LC_MONETARY=</varname></term>
|
||
<term><varname>locale.LC_MESSAGES=</varname></term>
|
||
<term><varname>locale.LC_PAPER=</varname></term>
|
||
<term><varname>locale.LC_NAME=</varname></term>
|
||
<term><varname>locale.LC_ADDRESS=</varname></term>
|
||
<term><varname>locale.LC_TELEPHONE=</varname></term>
|
||
<term><varname>locale.LC_MEASUREMENT=</varname></term>
|
||
<term><varname>locale.LC_IDENTIFICATION=</varname></term>
|
||
|
||
<listitem><para>Set the system locale to use. This overrides
|
||
the settings in <filename>/etc/locale.conf</filename>. For
|
||
more information, see
|
||
<citerefentry project='man-pages'><refentrytitle>locale.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>
|
||
and
|
||
<citerefentry project='man-pages'><refentrytitle>locale</refentrytitle><manvolnum>7</manvolnum></citerefentry>.
|
||
</para>
|
||
|
||
<xi:include href="version-info.xml" xpointer="v186"/></listitem>
|
||
</varlistentry>
|
||
</variablelist>
|
||
|
||
<para>For other kernel command line parameters understood by
|
||
components of the core OS, please refer to
|
||
<citerefentry><refentrytitle>kernel-command-line</refentrytitle><manvolnum>7</manvolnum></citerefentry>.</para>
|
||
</refsect1>
|
||
|
||
<refsect1>
|
||
<title>System Credentials</title>
|
||
|
||
<para>During initialization the service manager will import credentials from various sources into the
|
||
system's set of credentials, which can then be propagated into services and consumed by
|
||
generators:</para>
|
||
|
||
<itemizedlist>
|
||
<listitem><para>When the service manager first initializes it will read system credentials from SMBIOS
|
||
Type 11 vendor strings
|
||
<varname>io.systemd.credential:<replaceable>name</replaceable>=<replaceable>value</replaceable></varname>,
|
||
and
|
||
<varname>io.systemd.credential.binary:<replaceable>name</replaceable>=<replaceable>value</replaceable></varname>.</para></listitem>
|
||
|
||
<listitem><para>At the same time it will import credentials from QEMU <literal>fw_cfg</literal>. (Note
|
||
that the SMBIOS mechanism is generally preferred, because it is faster and generic.)</para></listitem>
|
||
|
||
<listitem><para>Credentials may be passed via the kernel command line, using the
|
||
<varname>systemd.set-credential=</varname> parameter, see above.</para></listitem>
|
||
|
||
<listitem><para>Credentials may be passed from the UEFI environment via
|
||
<citerefentry><refentrytitle>systemd-stub</refentrytitle><manvolnum>7</manvolnum></citerefentry>.</para></listitem>
|
||
|
||
<listitem><para>When the service manager is invoked during the initrd → host transition it will import
|
||
all files in <filename>/run/credentials/@initrd/</filename> as system credentials.</para></listitem>
|
||
</itemizedlist>
|
||
|
||
<para>Invoke
|
||
<citerefentry><refentrytitle>systemd-creds</refentrytitle><manvolnum>1</manvolnum></citerefentry> as
|
||
follows to see the list of credentials passed into the system:</para>
|
||
|
||
<programlisting># systemd-creds --system list</programlisting>
|
||
|
||
<para>For further information see <ulink url="https://systemd.io/CREDENTIALS">System and Service
|
||
Credentials</ulink> documentation.</para>
|
||
|
||
<para>The service manager when run as PID 1 consumes the following system credentials:</para>
|
||
|
||
<variablelist class='system-credentials'>
|
||
<varlistentry>
|
||
<term><varname>vmm.notify_socket</varname></term>
|
||
<listitem>
|
||
<para>Contains a <constant>AF_VSOCK</constant> or <constant>AF_UNIX</constant> address where to
|
||
send a <constant>READY=1</constant> notification message when the service manager has completed
|
||
booting. See
|
||
<citerefentry><refentrytitle>sd_notify</refentrytitle><manvolnum>3</manvolnum></citerefentry> and
|
||
the next section for more information. Note that in case the hypervisor does not support
|
||
<constant>SOCK_DGRAM</constant> over <constant>AF_VSOCK</constant>,
|
||
<constant>SOCK_SEQPACKET</constant> will be tried instead. The credential payload for
|
||
<constant>AF_VSOCK</constant> should be a string in the form
|
||
<literal>vsock:CID:PORT</literal>. <literal>vsock-stream</literal>, <literal>vsock-dgram</literal>
|
||
and <literal>vsock-seqpacket</literal> can be used instead of <literal>vsock</literal> to force
|
||
usage of the corresponding socket type.</para>
|
||
|
||
<para>This feature is useful for machine managers or other processes on the host to receive a
|
||
notification via VSOCK when a virtual machine has finished booting.</para>
|
||
|
||
<xi:include href="version-info.xml" xpointer="v254"/>
|
||
</listitem>
|
||
</varlistentry>
|
||
|
||
<varlistentry>
|
||
<term><varname>system.machine_id</varname></term>
|
||
<listitem>
|
||
<para>Takes a 128bit hexadecimal ID to initialize <filename>/etc/machine-id</filename> from, if the
|
||
file is not set up yet. See
|
||
<citerefentry><refentrytitle>machine-id</refentrytitle><manvolnum>5</manvolnum></citerefentry> for
|
||
details.</para>
|
||
|
||
<xi:include href="version-info.xml" xpointer="v254"/>
|
||
</listitem>
|
||
</varlistentry>
|
||
</variablelist>
|
||
|
||
<para>For a list of system credentials various other components of systemd consume, see
|
||
<citerefentry><refentrytitle>systemd.system-credentials</refentrytitle><manvolnum>7</manvolnum></citerefentry>.</para>
|
||
</refsect1>
|
||
|
||
<refsect1>
|
||
<title>Readiness Protocol</title>
|
||
|
||
<para>The service manager implements a readiness notification protocol both between the manager and its
|
||
services (i.e. down the stack), and between the manager and a potential supervisor further up the stack
|
||
(the latter could be a machine or container manager, or in case of a per-user service manager the system
|
||
service manager instance). The basic protocol (and the suggested API for it) is described in
|
||
<citerefentry><refentrytitle>sd_notify</refentrytitle><manvolnum>3</manvolnum></citerefentry>.</para>
|
||
|
||
<para>The notification socket the service manager (including PID 1) uses for reporting readiness to its
|
||
own supervisor is set via the usual <varname>$NOTIFY_SOCKET</varname> environment variable (see
|
||
above). Since this is directly settable only for container managers and for the per-user instance of the
|
||
service manager, an additional mechanism to configure this is available, in particular intended for use
|
||
in VM environments: the <varname>vmm.notify_socket</varname> system credential (see above) may be set to
|
||
a suitable socket (typically an <constant>AF_VSOCK</constant> one) via SMBIOS Type 11 vendor strings. For
|
||
details see above.</para>
|
||
|
||
<para>The notification protocol from the service manager up the stack towards a supervisor supports a
|
||
number of extension fields that allow a supervisor to learn about specific properties of the system and
|
||
track its boot progress. Specifically the following fields are sent:</para>
|
||
|
||
<itemizedlist>
|
||
<listitem><para>An <varname>X_SYSTEMD_HOSTNAME=…</varname> message will be sent out once the initial
|
||
hostname for the system has been determined. Note that during later runtime the hostname might be
|
||
changed again programmatically, and (currently) no further notifications are sent out in that case.</para>
|
||
|
||
<xi:include href="version-info.xml" xpointer="v256"/></listitem>
|
||
|
||
<listitem><para>An <varname>X_SYSTEMD_MACHINE_ID=…</varname> message will be sent out once the machine
|
||
ID of the system has been determined. See
|
||
<citerefentry><refentrytitle>machine-id</refentrytitle><manvolnum>5</manvolnum></citerefentry> for
|
||
details.</para>
|
||
|
||
<xi:include href="version-info.xml" xpointer="v256"/></listitem>
|
||
|
||
<listitem><para>An <varname>X_SYSTEMD_SIGNALS_LEVEL=…</varname> message will be sent out once the
|
||
service manager installed the various UNIX process signal handlers described above. The field's value
|
||
is an unsigned integer formatted as decimal string, and indicates the supported UNIX process signal
|
||
feature level of the service manager. Currently, only a single feature level is defined:</para>
|
||
|
||
<itemizedlist>
|
||
<listitem><para><varname>X_SYSTEMD_SIGNALS_LEVEL=2</varname> covers the various UNIX process signals
|
||
documented above – which are a superset of those supported by the historical SysV init
|
||
system.</para></listitem>
|
||
</itemizedlist>
|
||
|
||
<para>Signals sent to PID 1 before this message is sent might not be handled correctly yet. A consumer
|
||
of these messages should parse the value as an unsigned integer indication the level of support. For
|
||
now only the mentioned level 2 is defined, but later on additional levels might be defined with higher
|
||
integers, that will implement a superset of the currently defined behaviour.</para>
|
||
|
||
<xi:include href="version-info.xml" xpointer="v256"/></listitem>
|
||
|
||
<listitem><para><varname>X_SYSTEMD_UNIT_ACTIVE=…</varname> and
|
||
<varname>X_SYSTEMD_UNIT_INACTIVE=…</varname> messages will be sent out for each target unit as it
|
||
becomes active or stops being active. This is useful to track boot progress and functionality. For
|
||
example, once the <filename>ssh-access.target</filename> unit is reported started SSH access is
|
||
typically available, see
|
||
<citerefentry><refentrytitle>systemd.special</refentrytitle><manvolnum>7</manvolnum></citerefentry> for
|
||
details.</para>
|
||
|
||
<xi:include href="version-info.xml" xpointer="v256"/></listitem>
|
||
|
||
<listitem><para>An <varname>X_SYSTEMD_SHUTDOWN=…</varname> message will be sent out very shortly before
|
||
the system shuts down. The value is one of the strings <literal>reboot</literal>,
|
||
<literal>halt</literal>, <literal>poweroff</literal>, <literal>kexec</literal> and indicates which kind
|
||
of shutdown is being executed.</para>
|
||
|
||
<xi:include href="version-info.xml" xpointer="v256"/></listitem>
|
||
|
||
<listitem><para>An <varname>X_SYSTEMD_REBOOT_PARAMETER=…</varname> message will also be sent out very
|
||
shortly before the system shuts down. Its value is the reboot argument as configured with
|
||
<command>systemctl --reboot-argument=…</command>.</para>
|
||
|
||
<xi:include href="version-info.xml" xpointer="v256"/></listitem>
|
||
</itemizedlist>
|
||
|
||
<para>Note that these extension fields are sent in addition to the regular <literal>READY=1</literal> and
|
||
<literal>RELOADING=1</literal> notifications.</para>
|
||
</refsect1>
|
||
|
||
<refsect1>
|
||
<title>Options</title>
|
||
|
||
<para><command>systemd</command> is only very rarely invoked directly, since it is started early and is
|
||
already running by the time users may interact with it. Normally, tools like
|
||
<citerefentry><refentrytitle>systemctl</refentrytitle><manvolnum>1</manvolnum></citerefentry> are used to
|
||
give commands to the manager. Since <command>systemd</command> is usually not invoked directly, the
|
||
options listed below are mostly useful for debugging and special purposes.</para>
|
||
|
||
<refsect2>
|
||
<title>Introspection and debugging options</title>
|
||
|
||
<para>Those options are used for testing and introspection, and <command>systemd</command> may
|
||
be invoked with them at any time:</para>
|
||
|
||
<variablelist>
|
||
<varlistentry>
|
||
<term><option>--dump-configuration-items</option></term>
|
||
|
||
<listitem><para>Dump understood unit configuration items. This outputs a terse but complete list of
|
||
configuration items understood in unit definition files.</para></listitem>
|
||
</varlistentry>
|
||
|
||
<varlistentry>
|
||
<term><option>--dump-bus-properties</option></term>
|
||
|
||
<listitem><para>Dump exposed bus properties. This outputs a terse but complete list of properties
|
||
exposed on D-Bus.</para>
|
||
|
||
<xi:include href="version-info.xml" xpointer="v239"/></listitem>
|
||
</varlistentry>
|
||
|
||
<varlistentry>
|
||
<term><option>--test</option></term>
|
||
|
||
<listitem><para>Determine the initial start-up transaction (i.e. the list of jobs enqueued at
|
||
start-up), dump it and exit — without actually executing any of the determined jobs. This option is
|
||
useful for debugging only. Note that during regular service manager start-up additional units not
|
||
shown by this operation may be started, because hardware, socket, bus or other kinds of activation
|
||
might add additional jobs as the transaction is executed. Use <option>--system</option> to request
|
||
the initial transaction of the system service manager (this is also the implied default), combine
|
||
with <option>--user</option> to request the initial transaction of the per-user service manager
|
||
instead.</para></listitem>
|
||
</varlistentry>
|
||
|
||
<varlistentry>
|
||
<term><option>--system</option></term>
|
||
<term><option>--user</option></term>
|
||
|
||
<listitem><para>When used in conjunction with <option>--test</option>, selects whether to calculate
|
||
the initial transaction for the system instance or for a per-user instance. These options have no
|
||
effect when invoked without <option>--test</option>, as during regular
|
||
(i.e. non-<option>--test</option>) invocations the service manager will automatically detect
|
||
whether it shall operate in system or per-user mode, by checking whether the PID it is run as is 1
|
||
or not. Note that it is not supported booting and maintaining a system with the service manager
|
||
running in <option>--system</option> mode but with a PID other than 1.</para></listitem>
|
||
</varlistentry>
|
||
|
||
<xi:include href="standard-options.xml" xpointer="help" />
|
||
<xi:include href="standard-options.xml" xpointer="version" />
|
||
</variablelist>
|
||
</refsect2>
|
||
|
||
<refsect2>
|
||
<title>Options that duplicate kernel command line settings</title>
|
||
|
||
<para>Those options correspond directly to options listed above in "Kernel Command Line". Both forms
|
||
may be used equivalently for the system manager, but it is recommended to use the forms listed above in
|
||
this context, because they are properly namespaced. When an option is specified both on the kernel
|
||
command line and as a normal command line argument, the latter has higher precedence.</para>
|
||
|
||
<para>When <command>systemd</command> is used as a user manager, the kernel command line is ignored and
|
||
only the options described below are understood. Nevertheless, <command>systemd</command> is usually
|
||
started in this mode through the
|
||
<citerefentry><refentrytitle>user@.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>
|
||
service, which is shared between all users. It may be more convenient to use configuration files to
|
||
modify settings (see
|
||
<citerefentry><refentrytitle>systemd-user.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>),
|
||
or environment variables. See the "Environment" section above for a discussion of how the environment
|
||
block is set.</para>
|
||
|
||
<variablelist>
|
||
<varlistentry>
|
||
<term><option>--unit=</option></term>
|
||
|
||
<listitem><para>Set default unit to activate on startup. If not specified, defaults to
|
||
<filename>default.target</filename>. See <varname>systemd.unit=</varname> above.</para></listitem>
|
||
</varlistentry>
|
||
|
||
<varlistentry>
|
||
<term><option>--dump-core</option></term>
|
||
|
||
<listitem><para>Enable core dumping on crash. This switch has no effect when running as user
|
||
instance. Same as <varname>systemd.dump_core=</varname> above.</para></listitem>
|
||
</varlistentry>
|
||
|
||
<varlistentry>
|
||
<term><option>--crash-vt=<replaceable>VT</replaceable></option></term>
|
||
|
||
<listitem><para>Switch to a specific virtual console (VT) on crash. This switch has no effect when
|
||
running as user instance. Same as <varname>systemd.crash_chvt=</varname> above (but not the
|
||
different spelling!).</para>
|
||
|
||
<xi:include href="version-info.xml" xpointer="v227"/></listitem>
|
||
</varlistentry>
|
||
|
||
<varlistentry>
|
||
<term><option>--crash-shell</option></term>
|
||
|
||
<listitem><para>Run a shell on crash. This switch has no effect when running as user instance. See
|
||
<varname>systemd.crash_shell=</varname> above.</para></listitem>
|
||
</varlistentry>
|
||
|
||
<varlistentry>
|
||
<term><option>--crash-action=</option></term>
|
||
|
||
<listitem><para>Specify what to do when the system manager (PID 1) crashes. This switch has no
|
||
effect when systemd is running as user instance. See <varname>systemd.crash_action=</varname>
|
||
above.</para>
|
||
|
||
<xi:include href="version-info.xml" xpointer="v256"/></listitem>
|
||
</varlistentry>
|
||
|
||
<varlistentry>
|
||
<term><option>--confirm-spawn</option></term>
|
||
|
||
<listitem><para>Ask for confirmation when spawning processes. This switch has no effect when run as
|
||
user instance. See <varname>systemd.confirm_spawn</varname> above.</para></listitem>
|
||
</varlistentry>
|
||
|
||
<varlistentry>
|
||
<term><option>--show-status</option></term>
|
||
|
||
<listitem><para>Show terse unit status information on the console during boot-up and shutdown. See
|
||
<varname>systemd.show_status</varname> above.</para>
|
||
|
||
<xi:include href="version-info.xml" xpointer="v244"/></listitem>
|
||
</varlistentry>
|
||
|
||
<varlistentry>
|
||
<term><option>--log-color</option></term>
|
||
|
||
<listitem><para>Highlight important log messages. See <varname>systemd.log_color</varname> above.
|
||
</para>
|
||
|
||
<xi:include href="version-info.xml" xpointer="v244"/></listitem>
|
||
</varlistentry>
|
||
|
||
<varlistentry>
|
||
<term><option>--log-level=</option></term>
|
||
|
||
<listitem><para>Set log level. See <varname>systemd.log_level</varname> above.</para></listitem>
|
||
</varlistentry>
|
||
|
||
<varlistentry>
|
||
<term><option>--log-location</option></term>
|
||
|
||
<listitem><para>Include code location in log messages. See <varname>systemd.log_location</varname>
|
||
above.</para>
|
||
|
||
<xi:include href="version-info.xml" xpointer="v244"/></listitem>
|
||
</varlistentry>
|
||
|
||
<varlistentry>
|
||
<term><option>--log-target=</option></term>
|
||
|
||
<listitem><para>Set log target. See <varname>systemd.log_target</varname> above.</para></listitem>
|
||
</varlistentry>
|
||
|
||
<varlistentry>
|
||
<term><option>--log-time=</option></term>
|
||
|
||
<listitem><para>Prefix console messages with timestamp. See <varname>systemd.log_time</varname> above.
|
||
</para>
|
||
|
||
<xi:include href="version-info.xml" xpointer="v246"/></listitem>
|
||
</varlistentry>
|
||
|
||
<varlistentry>
|
||
<term><option>--machine-id=</option></term>
|
||
|
||
<listitem><para>Override the machine-id set on the hard drive. See
|
||
<varname>systemd.machine_id=</varname> above.</para>
|
||
|
||
<xi:include href="version-info.xml" xpointer="v229"/></listitem>
|
||
</varlistentry>
|
||
|
||
<varlistentry>
|
||
<term><option>--service-watchdogs</option></term>
|
||
|
||
<listitem><para>Globally enable/disable all service watchdog timeouts and emergency actions. See
|
||
<varname>systemd.service_watchdogs</varname> above.</para>
|
||
|
||
<xi:include href="version-info.xml" xpointer="v237"/></listitem>
|
||
</varlistentry>
|
||
|
||
<varlistentry>
|
||
<term><option>--default-standard-output=</option></term>
|
||
<term><option>--default-standard-error=</option></term>
|
||
|
||
<listitem><para>Sets the default output or error output for all services and sockets,
|
||
respectively. See <varname>systemd.default_standard_output=</varname> and
|
||
<varname>systemd.default_standard_error=</varname> above.</para></listitem>
|
||
</varlistentry>
|
||
</variablelist>
|
||
</refsect2>
|
||
</refsect1>
|
||
|
||
<refsect1>
|
||
<title>System clock epoch</title>
|
||
|
||
<para>When <command>systemd</command> is started or restarted, it may set the system clock to the
|
||
"epoch". This mechanism is used to ensure that the system clock remains somewhat reasonably initialized
|
||
and roughly monotonic across reboots, in case no battery-backed local RTC is available or it does not
|
||
work correctly.</para>
|
||
|
||
<para>The epoch is the lowest date above which the system clock time is assumed to be set correctly. When
|
||
initializing, the local clock is <emphasis>advanced</emphasis> to the epoch if it was set to a lower
|
||
value. As a special case, if the local clock is sufficiently far in the future (by default 15 years, but
|
||
this can be configured at build time), the hardware clock is assumed to be broken, and the system clock
|
||
is <emphasis>rewound</emphasis> to the epoch.</para>
|
||
|
||
<para>The epoch is set to the highest of: the build time of <filename>systemd</filename>, the
|
||
modification time ("mtime") of <filename>/usr/lib/clock-epoch</filename>, and the modification time of
|
||
<filename>/var/lib/systemd/timesync/clock</filename>.</para>
|
||
</refsect1>
|
||
|
||
<refsect1>
|
||
<title>Files</title>
|
||
|
||
<variablelist>
|
||
<varlistentry>
|
||
<term><filename>/run/systemd/notify</filename></term>
|
||
|
||
<listitem><para>Daemon status notification socket. This is an
|
||
<constant>AF_UNIX</constant> datagram socket and is used to
|
||
implement the daemon notification logic as implemented by
|
||
<citerefentry><refentrytitle>sd_notify</refentrytitle><manvolnum>3</manvolnum></citerefentry>.</para></listitem>
|
||
|
||
</varlistentry>
|
||
|
||
<varlistentry>
|
||
<term><filename>/run/systemd/private</filename></term>
|
||
|
||
<listitem><para>Used internally as communication channel
|
||
between
|
||
<citerefentry><refentrytitle>systemctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>
|
||
and the systemd process. This is an
|
||
<constant>AF_UNIX</constant> stream socket. This interface is
|
||
private to systemd and should not be used in external
|
||
projects.</para></listitem>
|
||
</varlistentry>
|
||
|
||
<varlistentry>
|
||
<term><filename>/dev/initctl</filename></term>
|
||
|
||
<listitem><para>Limited compatibility support for the SysV
|
||
client interface, as implemented by the
|
||
<filename>systemd-initctl.service</filename> unit. This is a
|
||
named pipe in the file system. This interface is obsolete and
|
||
should not be used in new applications.</para></listitem>
|
||
</varlistentry>
|
||
|
||
<varlistentry>
|
||
<term><filename>/usr/lib/clock-epoch</filename></term>
|
||
|
||
<listitem><para>The modification time ("mtime") of this file is used for the time epoch, see previous
|
||
section.</para>
|
||
|
||
<xi:include href="version-info.xml" xpointer="v247"/></listitem>
|
||
</varlistentry>
|
||
|
||
<varlistentry>
|
||
<term><filename>/var/lib/systemd/timesync/clock</filename></term>
|
||
|
||
<listitem><para>The modification time ("mtime") of this file is updated by
|
||
<citerefentry><refentrytitle>systemd-timesyncd.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>.
|
||
If present, the modification time of file is used for the epoch, see previous section.
|
||
</para>
|
||
|
||
<xi:include href="version-info.xml" xpointer="v257"/></listitem>
|
||
</varlistentry>
|
||
</variablelist>
|
||
</refsect1>
|
||
|
||
<refsect1>
|
||
<title>History</title>
|
||
|
||
<variablelist>
|
||
<varlistentry>
|
||
<term>systemd 252</term>
|
||
<listitem><para>Kernel command-line arguments <varname>systemd.unified_cgroup_hierarchy</varname>
|
||
and <varname>systemd.legacy_systemd_cgroup_controller</varname> were deprecated. Please switch to
|
||
the unified cgroup hierarchy.</para>
|
||
|
||
<xi:include href="version-info.xml" xpointer="v252"/></listitem>
|
||
</varlistentry>
|
||
</variablelist>
|
||
</refsect1>
|
||
|
||
<refsect1>
|
||
<title>See Also</title>
|
||
<para><simplelist type="inline">
|
||
<member>The <ulink url="https://systemd.io/">systemd Homepage</ulink></member>
|
||
<member><citerefentry><refentrytitle>systemd-system.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry></member>
|
||
<member><citerefentry project='man-pages'><refentrytitle>locale.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry></member>
|
||
<member><citerefentry><refentrytitle>systemctl</refentrytitle><manvolnum>1</manvolnum></citerefentry></member>
|
||
<member><citerefentry><refentrytitle>journalctl</refentrytitle><manvolnum>1</manvolnum></citerefentry></member>
|
||
<member><citerefentry><refentrytitle>systemd-notify</refentrytitle><manvolnum>1</manvolnum></citerefentry></member>
|
||
<member><citerefentry><refentrytitle>daemon</refentrytitle><manvolnum>7</manvolnum></citerefentry></member>
|
||
<member><citerefentry><refentrytitle>sd-daemon</refentrytitle><manvolnum>3</manvolnum></citerefentry></member>
|
||
<member><citerefentry><refentrytitle>org.freedesktop.systemd1</refentrytitle><manvolnum>5</manvolnum></citerefentry></member>
|
||
<member><citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry></member>
|
||
<member><citerefentry><refentrytitle>systemd.special</refentrytitle><manvolnum>7</manvolnum></citerefentry></member>
|
||
<member><citerefentry project='die-net'><refentrytitle>pkg-config</refentrytitle><manvolnum>1</manvolnum></citerefentry></member>
|
||
<member><citerefentry><refentrytitle>kernel-command-line</refentrytitle><manvolnum>7</manvolnum></citerefentry></member>
|
||
<member><citerefentry project='man-pages'><refentrytitle>bootup</refentrytitle><manvolnum>7</manvolnum></citerefentry></member>
|
||
<member><citerefentry><refentrytitle>systemd.directives</refentrytitle><manvolnum>7</manvolnum></citerefentry></member>
|
||
</simplelist></para>
|
||
|
||
<para>For more information about the concepts and
|
||
ideas behind systemd, please refer to the
|
||
<ulink url="https://0pointer.de/blog/projects/systemd.html">Original Design Document</ulink>.</para>
|
||
</refsect1>
|
||
|
||
</refentry>
|