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diff --git a/man/systemd.xml b/man/systemd.xml new file mode 100644 index 0000000..5287bda --- /dev/null +++ b/man/systemd.xml @@ -0,0 +1,1263 @@ +<?xml version='1.0'?> +<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN" + "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd"> + +<!-- + SPDX-License-Identifier: LGPL-2.1+ +--> + +<refentry id="systemd" + xmlns:xi="http://www.w3.org/2001/XInclude"> + + <refentryinfo> + <title>systemd</title> + <productname>systemd</productname> + </refentryinfo> + + <refmeta> + <refentrytitle>systemd</refentrytitle> + <manvolnum>1</manvolnum> + </refmeta> + + <refnamediv> + <refname>systemd</refname> + <refname>init</refname> + <refpurpose>systemd system and service manager</refpurpose> + </refnamediv> + + <refsynopsisdiv> + <cmdsynopsis> + <command>/usr/lib/systemd/systemd</command> + <arg choice="opt" rep="repeat">OPTIONS</arg> + </cmdsynopsis> + <cmdsynopsis> + <command>init</command> + <arg choice="opt" rep="repeat">OPTIONS</arg> + <arg choice="req">COMMAND</arg> + </cmdsynopsis> + </refsynopsisdiv> + + <refsect1> + <title>Description</title> + + <para>systemd is a system and service manager for Linux operating + systems. When run as first process on boot (as PID 1), it acts as + init system that brings up and maintains userspace + services.</para> + + <para>For compatibility with SysV, if systemd is called as + <command>init</command> and a PID that is not 1, it will execute + <command>telinit</command> and pass all command line arguments + unmodified. That means <command>init</command> and + <command>telinit</command> are mostly equivalent when invoked from + normal login sessions. See + <citerefentry><refentrytitle>telinit</refentrytitle><manvolnum>8</manvolnum></citerefentry> + for more information.</para> + + <para>When run as a system instance, systemd interprets the + configuration file <filename>system.conf</filename> and the files + in <filename>system.conf.d</filename> directories; when run as a + user instance, systemd interprets the configuration file + <filename>user.conf</filename> and the files in + <filename>user.conf.d</filename> directories. See + <citerefentry><refentrytitle>systemd-system.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry> + for more information.</para> + </refsect1> + + <refsect1> + <title>Options</title> + + <para>The following options are understood:</para> + + <variablelist> + <varlistentry> + <term><option>--test</option></term> + + <listitem><para>Determine startup sequence, dump it and exit. + This is an option useful for debugging only.</para></listitem> + </varlistentry> + <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 to dbus. + </para></listitem> + </varlistentry> + <varlistentry> + <term><option>--unit=</option></term> + + <listitem><para>Set default unit to activate on startup. If + not specified, defaults to + <filename>default.target</filename>.</para></listitem> + </varlistentry> + <varlistentry> + <term><option>--system</option></term> + <term><option>--user</option></term> + + <listitem><para>For <option>--system</option>, tell systemd to + run a system instance, even if the process ID is not 1, i.e. + systemd is not run as init process. <option>--user</option> + does the opposite, running a user instance even if the process + ID is 1. Normally, it should not be necessary to pass these + options, as systemd automatically detects the mode it is + started in. These options are hence of little use except for + debugging. Note that it is not supported booting and + maintaining a full system with systemd running in + <option>--system</option> mode, but PID not 1. In practice, + passing <option>--system</option> explicitly is only useful in + conjunction with <option>--test</option>.</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. This setting may also + be enabled during boot on the kernel command line via the + <varname>systemd.dump_core=</varname> option, see + below.</para></listitem> + </varlistentry> + + <varlistentry> + <term><option>--crash-vt=</option><replaceable>VT</replaceable></term> + + <listitem><para>Switch to a specific virtual console (VT) on + crash. Takes a positive integer in the range 1–63, or a + boolean argument. If an integer is passed, selects which VT to + switch to. If <constant>yes</constant>, the VT kernel messages + are written to is selected. If <constant>no</constant>, no VT + switch is attempted. This switch has no effect when running as + user instance. This setting may also be enabled during boot, + on the kernel command line via the + <varname>systemd.crash_vt=</varname> option, see + <!-- FIXME: there is no crash_vt command line option? --> + below.</para></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. This setting may also be + enabled during boot, on the kernel command line via the + <varname>systemd.crash_shell=</varname> option, see + below.</para></listitem> + </varlistentry> + + <varlistentry> + <term><option>--crash-reboot</option></term> + + <listitem><para>Automatically reboot the system on crash. This + switch has no effect when running as user instance. This + setting may also be enabled during boot, on the kernel command + line via the <varname>systemd.crash_reboot=</varname> option, + see below.</para></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.</para></listitem> + </varlistentry> + <varlistentry> + <term><option>--show-status=</option></term> + + <listitem><para>Takes a boolean argument or the special value <constant>auto</constant>. If on, terse unit + status information is shown on the console during boot-up and shutdown. If off, no such status information is + shown. If set to <constant>auto</constant> behavior is similar to off, except that it is automatically switched + to on, as soon as the first unit failure or significant boot delay is encountered. This switch has no effect + when invoked as user instance. If specified, overrides both the kernel command line setting + <varname>systemd.show_status=</varname> (see below) and the configuration file option + <option>ShowStatus=</option>, see + <citerefentry><refentrytitle>systemd-system.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem> + </varlistentry> + <varlistentry> + <term><option>--log-target=</option></term> + + <listitem><para>Set log target. Argument must be one of + <option>console</option>, + <option>journal</option>, + <option>kmsg</option>, + <option>journal-or-kmsg</option>, + <option>null</option>.</para></listitem> + </varlistentry> + <varlistentry> + <term><option>--log-level=</option></term> + + <listitem><para>Set log level. As + argument this accepts a numerical log + level or the well-known <citerefentry project='man-pages'><refentrytitle>syslog</refentrytitle><manvolnum>3</manvolnum></citerefentry> + symbolic names (lowercase): + <option>emerg</option>, + <option>alert</option>, + <option>crit</option>, + <option>err</option>, + <option>warning</option>, + <option>notice</option>, + <option>info</option>, + <option>debug</option>.</para></listitem> + </varlistentry> + <varlistentry> + <term><option>--log-color=</option></term> + + <listitem><para>Highlight important log messages. Argument is + a boolean value. If the argument is omitted, it defaults to + <option>true</option>.</para></listitem> + </varlistentry> + <varlistentry> + <term><option>--log-location=</option></term> + + <listitem><para>Include code location in log messages. This is + mostly relevant for debugging purposes. Argument is a boolean + value. If the argument is omitted it defaults to + <option>true</option>.</para></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. 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>syslog</option>, + <option>syslog+console</option>, + <option>kmsg</option>, + <option>kmsg+console</option>. If the + argument is omitted + <option>--default-standard-output=</option> defaults to + <option>journal</option> and + <option>--default-standard-error=</option> to + <option>inherit</option>.</para></listitem> + </varlistentry> + + <varlistentry> + <term><option>--machine-id=</option></term> + + <listitem><para>Override the machine-id set on the hard drive, + useful for network booting or for containers. May not be set + to all zeros.</para></listitem> + </varlistentry> + + <varlistentry> + <term><option>--service-watchdogs=</option></term> + + <listitem><para>Globally enable/disable all service watchdog timeouts and emergency + actions. This setting may also be specified during boot, on the kernel + command line via the <varname>systemd.service_watchdogs=</varname> + option, see below. Defaults to enabled.</para></listitem> + </varlistentry> + + <xi:include href="standard-options.xml" xpointer="help" /> + <xi:include href="standard-options.xml" xpointer="version" /> + </variablelist> + </refsect1> + + <refsect1> + <title>Concepts</title> + + <para>systemd provides a dependency system between various + entities called "units" of 11 different types. Units encapsulate + various objects that are relevant for system boot-up and + maintenance. The majority of units are configured in unit + configuration files, whose syntax and basic set of options is + described in + <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>, + however some are created automatically from other configuration, + dynamically from system state or programmatically at runtime. + Units may be "active" (meaning started, bound, plugged in, …, + depending on the unit type, see below), or "inactive" (meaning + stopped, unbound, unplugged, …), as well as in the process of + being activated or deactivated, i.e. between the two states (these + states are called "activating", "deactivating"). A special + "failed" state is available as well, which is very similar to + "inactive" and is entered when the service failed in some way + (process returned error code on exit, or crashed, an operation + timed out, or after too many restarts). If this state is entered, + the cause will be logged, for later reference. Note that the + various unit types may have a number of additional substates, + which are mapped to the five generalized unit states described + here.</para> + + <para>The following unit types are available:</para> + + <orderedlist> + <listitem><para>Service units, which start and control daemons + and the processes they consist of. For details, see + <citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem> + + <listitem><para>Socket units, which encapsulate local IPC or + network sockets in the system, useful for socket-based + activation. For details about socket units, see + <citerefentry><refentrytitle>systemd.socket</refentrytitle><manvolnum>5</manvolnum></citerefentry>, + for details on socket-based activation and other forms of + activation, see + <citerefentry><refentrytitle>daemon</refentrytitle><manvolnum>7</manvolnum></citerefentry>.</para></listitem> + + <listitem><para>Target units are useful to group units, or + provide well-known synchronization points during boot-up, see + <citerefentry><refentrytitle>systemd.target</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem> + + <listitem><para>Device units expose kernel devices in systemd + and may be used to implement device-based activation. For + details, see + <citerefentry><refentrytitle>systemd.device</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem> + + <listitem><para>Mount units control mount points in the file + system, for details see + <citerefentry><refentrytitle>systemd.mount</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem> + + <listitem><para>Automount units provide automount capabilities, + for on-demand mounting of file systems as well as parallelized + boot-up. See + <citerefentry><refentrytitle>systemd.automount</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem> + + <listitem><para>Timer units are useful for triggering activation + of other units based on timers. You may find details in + <citerefentry><refentrytitle>systemd.timer</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem> + + <listitem><para>Swap units are very similar to mount units and + encapsulate memory swap partitions or files of the operating + system. They are described in + <citerefentry><refentrytitle>systemd.swap</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem> + + <listitem><para>Path units may be used to activate other + services when file system objects change or are modified. See + <citerefentry><refentrytitle>systemd.path</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem> + + <listitem><para>Slice units may be used to group units which + manage system processes (such as service and scope units) in a + hierarchical tree for resource management purposes. See + <citerefentry><refentrytitle>systemd.slice</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem> + + <listitem><para>Scope units are similar to service units, but + manage foreign processes instead of starting them as well. See + <citerefentry><refentrytitle>systemd.scope</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem> + + </orderedlist> + + <para>Units are named as their configuration files. Some units + have special semantics. A detailed list is available in + <citerefentry><refentrytitle>systemd.special</refentrytitle><manvolnum>7</manvolnum></citerefentry>.</para> + + <para>systemd knows various kinds of dependencies, including + positive and negative requirement dependencies (i.e. + <varname>Requires=</varname> and <varname>Conflicts=</varname>) as + well as ordering dependencies (<varname>After=</varname> and + <varname>Before=</varname>). NB: ordering and requirement + dependencies are orthogonal. If only a requirement dependency + exists between two units (e.g. <filename>foo.service</filename> + requires <filename>bar.service</filename>), but no ordering + dependency (e.g. <filename>foo.service</filename> after + <filename>bar.service</filename>) and both are requested to start, + they will be started in parallel. It is a common pattern that both + requirement and ordering dependencies are placed between two + units. Also note that the majority of dependencies are implicitly + created and maintained by systemd. In most cases, it should be + unnecessary to declare additional dependencies manually, however + it is possible to do this.</para> + + <para>Application programs and units (via dependencies) may + request state changes of units. In systemd, these requests are + encapsulated as 'jobs' and maintained in a job queue. Jobs may + succeed or can fail, their execution is ordered based on the + ordering dependencies of the units they have been scheduled + for.</para> + + <para>On boot systemd activates the target unit + <filename>default.target</filename> whose job is to activate + on-boot services and other on-boot units by pulling them in via + dependencies. Usually, the unit name is just an alias (symlink) for + either <filename>graphical.target</filename> (for fully-featured + boots into the UI) or <filename>multi-user.target</filename> (for + limited console-only boots for use in embedded or server + environments, or similar; a subset of graphical.target). However, + it is at the discretion of the administrator to configure it as an + alias to any other target unit. See + <citerefentry><refentrytitle>systemd.special</refentrytitle><manvolnum>7</manvolnum></citerefentry> + for details about these target units.</para> + + <para>systemd only keeps a minimal set of units loaded into memory. Specifically, the only units that are kept + loaded into memory are those for which at least one of the following conditions is true:</para> + + <orderedlist> + <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> + <listitem><para>It has a job queued for it</para></listitem> + <listitem><para>It is a dependency of some sort of at least one other unit that is loaded into memory</para></listitem> + <listitem><para>It has some form of resource still allocated (e.g. a service unit that is inactive but for which + a process is still lingering that ignored the request to be terminated)</para></listitem> + <listitem><para>It has been pinned into memory programmatically by a D-Bus call</para></listitem> + </orderedlist> + + <para>systemd will automatically and implicitly load units from disk — if they are not loaded yet — as soon as + operations are requested for them. Thus, in many respects, the fact whether a unit is loaded or not is invisible to + clients. Use <command>systemctl list-units --all</command> to comprehensively list all units currently loaded. Any + unit for which none of the conditions above applies is promptly unloaded. Note that when a unit is unloaded from + memory its accounting data is flushed out too. However, this data is generally not lost, as a journal log record + is generated declaring the consumed resources whenever a unit shuts down.</para> + + <para>Processes systemd spawns are placed in individual Linux + control groups named after the unit which they belong to in the + private systemd hierarchy. (see <ulink + url="https://www.kernel.org/doc/Documentation/cgroup-v1/cgroups.txt">cgroups.txt</ulink> + for more information about control groups, or short "cgroups"). + systemd uses this to effectively keep track of processes. Control + group information is maintained in the kernel, and is accessible + via the file system hierarchy (beneath + <filename>/sys/fs/cgroup/systemd/</filename>), or in tools such as + <citerefentry project='man-pages'><refentrytitle>systemd-cgls</refentrytitle><manvolnum>1</manvolnum></citerefentry> + or + <citerefentry project='man-pages'><refentrytitle>ps</refentrytitle><manvolnum>1</manvolnum></citerefentry> + (<command>ps xawf -eo pid,user,cgroup,args</command> is + particularly useful to list all processes and the systemd units + they belong to.).</para> + + <para>systemd is compatible with the SysV init system to a large + degree: SysV init scripts are supported and simply read as an + alternative (though limited) configuration file format. The SysV + <filename>/dev/initctl</filename> interface is provided, and + compatibility implementations of the various SysV client tools are + available. In addition to that, various established Unix + functionality such as <filename>/etc/fstab</filename> or the + <filename>utmp</filename> database are supported.</para> + + <para>systemd has a minimal transaction system: if a unit is + requested to start up or shut down it will add it and all its + dependencies to a temporary transaction. Then, it will verify if + the transaction is consistent (i.e. whether the ordering of all + units is cycle-free). If it is not, systemd will try to fix it up, + and removes non-essential jobs from the transaction that might + remove the loop. Also, systemd tries to suppress non-essential + jobs in the transaction that would stop a running service. Finally + it is checked whether the jobs of the transaction contradict jobs + that have already been queued, and optionally the transaction is + aborted then. If all worked out and the transaction is consistent + and minimized in its impact it is merged with all already + outstanding jobs and added to the run queue. Effectively this + means that before executing a requested operation, systemd will + verify that it makes sense, fixing it if possible, and only + failing if it really cannot work.</para> + + <para>Note that transactions are generated independently of a unit's + state at runtime, hence, for example, if a start job is requested on an + already started unit, it will still generate a transaction and wake up any + inactive dependencies (and cause propagation of other jobs as per the + defined relationships). This is because the enqueued job is at the time of + execution compared to the target unit's state and is marked successful and + complete when both satisfy. However, this job also pulls in other + dependencies due to the defined relationships and thus leads to, in our + our example, start jobs for any of those inactive units getting queued as + well.</para> + + <para>systemd contains native implementations of various tasks + that need to be executed as part of the boot process. For example, + it sets the hostname or configures the loopback network device. It + also sets up and mounts various API file systems, such as + <filename>/sys</filename> or <filename>/proc</filename>.</para> + + <para>For more information about the concepts and + ideas behind systemd, please refer to the + <ulink url="http://0pointer.de/blog/projects/systemd.html">Original Design Document</ulink>.</para> + + <para>Note that some but not all interfaces provided + by systemd are covered by the + <ulink url="https://www.freedesktop.org/wiki/Software/systemd/InterfaceStabilityPromise">Interface + Stability Promise</ulink>.</para> + + <para>Units may be generated dynamically at boot and system + 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> + + <para>Systems which invoke systemd in a container or initrd + environment should implement the + <ulink url="https://www.freedesktop.org/wiki/Software/systemd/ContainerInterface">Container Interface</ulink> or + <ulink url="https://www.freedesktop.org/wiki/Software/systemd/InitrdInterface">initrd Interface</ulink> + specifications, respectively.</para> + </refsect1> + + <refsect1> + <title>Directories</title> + + <variablelist> + <varlistentry> + <term>System unit directories</term> + + <listitem><para>The systemd system manager reads unit + configuration from various directories. Packages that want to + install unit files shall place them in the directory returned + 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="http://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> + + <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-irreversible</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-irreversible</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-irreversible</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-irreversible</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-irreversible</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-irreversible</command>.</para> + </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+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></listitem> + </varlistentry> + + <varlistentry> + <term><constant>SIGRTMIN+24</constant></term> + + <listitem><para>Immediately exits the manager (only available + for --user instances).</para></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></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></listitem> + </varlistentry> + </variablelist> + </refsect1> + + <refsect1> + <title>Environment</title> + + <variablelist class='environment-variables'> + <varlistentry> + <term><varname>$SYSTEMD_LOG_LEVEL</varname></term> + <listitem><para>systemd reads the log level from this + environment variable. This can be overridden with + <option>--log-level=</option>.</para></listitem> + </varlistentry> + + <varlistentry> + <term><varname>$SYSTEMD_LOG_TARGET</varname></term> + <listitem><para>systemd reads the log target from this + environment variable. This can be overridden with + <option>--log-target=</option>.</para></listitem> + </varlistentry> + + <varlistentry> + <term><varname>$SYSTEMD_LOG_COLOR</varname></term> + <listitem><para>Controls whether systemd highlights important + log messages. This can be overridden with + <option>--log-color=</option>.</para></listitem> + </varlistentry> + + <varlistentry> + <term><varname>$SYSTEMD_LOG_LOCATION</varname></term> + <listitem><para>Controls whether systemd prints the code + location along with log messages. This can be overridden with + <option>--log-location=</option>.</para></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="http://standards.freedesktop.org/basedir-spec/basedir-spec-latest.html">XDG + Base Directory specification</ulink> to find its + configuration.</para></listitem> + </varlistentry> + + <varlistentry> + <term><varname>$SYSTEMD_UNIT_PATH</varname></term> + + <listitem><para>Controls where systemd looks for unit + files.</para></listitem> + </varlistentry> + + <varlistentry> + <term><varname>$SYSTEMD_SYSVINIT_PATH</varname></term> + + <listitem><para>Controls where systemd looks for SysV init + scripts.</para></listitem> + </varlistentry> + + <varlistentry> + <term><varname>$SYSTEMD_SYSVRCND_PATH</varname></term> + + <listitem><para>Controls where systemd looks for SysV init + script runlevel link farms.</para></listitem> + </varlistentry> + + <varlistentry> + <term><varname>$SYSTEMD_COLORS</varname></term> + + <listitem><para>The value must be a boolean. Controls whether colorized output should be + generated. This can be specified to override the decision that <command>systemd</command> + makes based on <varname>$TERM</varname> and what the console is connected to.</para> + </listitem> + </varlistentry> + + <varlistentry> + <term><varname>$SYSTEMD_URLIFY</varname></term> + + <listitem><para>The value must be a boolean. Controls whether clickable links should be generated in the output + for terminal emulators supporting this. This can be specified to override the decision that + <command>systemd</command> makes based on <varname>$TERM</varname> and other conditions.</para> + </listitem> + </varlistentry> + + <varlistentry> + <term><varname>$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 systemd for supervised processes for + status and start-up completion notification. See + <citerefentry><refentrytitle>sd_notify</refentrytitle><manvolnum>3</manvolnum></citerefentry> + 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 system instance systemd parses a number of + kernel command line arguments<footnote><para>If run inside a Linux + container these arguments may be passed as command line arguments + 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> + instead.</para></footnote>:</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 initial RAM disk + (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> + </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 (VT) when it + crashes. Defaults to disabled, meaning that no such switch is attempted. If + set to enabled, the VT the kernel messages are written to is selected. + </para></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, after a 10s delay. Otherwise, no shell is spawned. Defaults + to disabled, for security reasons, as the shell is not protected by password + authentication.</para></listitem> + </varlistentry> + + <varlistentry> + <term><varname>systemd.crash_reboot</varname></term> + + <listitem><para>Takes a boolean argument or enables the option if specified + without an argument. If enabled, the system manager (PID 1) will reboot the + machine automatically when it crashes, after a 10s delay. Otherwise, the + system will hang indefinitely. Defaults to disabled, in order to avoid a + reboot loop. If combined with <varname>systemd.crash_shell</varname>, the + system is rebooted after the shell exits.</para></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></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></listitem> + </varlistentry> + + <varlistentry> + <term><varname>systemd.show_status</varname></term> + + <listitem><para>Takes a boolean argument or the constant + <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. + <constant>auto</constant> behaves like <option>false</option> until a unit + fails or 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>auto</constant>. If specified overrides the system + manager configuration file option <option>ShowStatus=</option>, see + <citerefentry><refentrytitle>systemd-system.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>. + However, the process command line option <option>--show-status=</option> + takes precedence over both this kernel command line option and the + configuration file option.</para></listitem> + </varlistentry> + + <varlistentry> + <term><varname>systemd.log_target=</varname></term> + <term><varname>systemd.log_level=</varname></term> + <term><varname>systemd.log_location=</varname></term> + <term><varname>systemd.log_color</varname></term> + + <listitem><para>Controls log output, with the same effect as the + <varname>$SYSTEMD_LOG_TARGET</varname>, + <varname>$SYSTEMD_LOG_LEVEL</varname>, + <varname>$SYSTEMD_LOG_LOCATION</varname>, + <varname>$SYSTEMD_LOG_COLOR</varname> environment variables described above. + <varname>systemd.log_color</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, with the same effect as the + <option>--default-standard-output=</option> and + <option>--default-standard-error=</option> command line + arguments described above, respectively.</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></listitem> + </varlistentry> + + <varlistentry> + <term><varname>systemd.unified_cgroup_hierarchy</varname></term> + + <listitem><para>When specified without an argument or with a true argument, + enables the usage of + <ulink url="https://www.kernel.org/doc/Documentation/cgroup-v2.txt">unified cgroup hierarchy</ulink> + (a.k.a. cgroups-v2). When specified with a false argument, fall back to + hybrid or full legacy cgroup hierarchy.</para> + + <para>If this option is not specified, the default behaviour is determined + during compilation (the <option>-Ddefault-hierarchy=</option> meson + option). If the kernel does not support unified cgroup hierarchy, the legacy + hierarchy will be used even if this option is specified.</para> + </listitem> + </varlistentry> + + <varlistentry> + <term><varname>systemd.legacy_systemd_cgroup_controller</varname></term> + + <listitem><para>Takes effect if the full unified cgroup hierarchy is not used + (see previous option). When specified without an argument or with a true + argument, disables the use of "hybrid" cgroup hierarchy (i.e. a cgroups-v2 + tree used for systemd, and + <ulink url="https://www.kernel.org/doc/Documentation/cgroup-v1/">legacy + cgroup hierarchy</ulink>, a.k.a. cgroups-v1, for other controllers), and + forces a full "legacy" mode. When specified with a false argument, enables + the use of "hybrid" hierarchy.</para> + + <para>If this option is not specified, the default behaviour is determined + during compilation (the <option>-Ddefault-hierarchy=</option> meson + option). If the kernel does not support unified cgroup hierarchy, the legacy + hierarchy will be used even if this option is specified.</para> + </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></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></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></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></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></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></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>Sockets and FIFOs</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> + </variablelist> + </refsect1> + + <refsect1> + <title>See Also</title> + <para> + The <ulink url="https://www.freedesktop.org/wiki/Software/systemd/">systemd Homepage</ulink>, + <citerefentry><refentrytitle>systemd-system.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>, + <citerefentry project='man-pages'><refentrytitle>locale.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>, + <citerefentry><refentrytitle>systemctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>, + <citerefentry><refentrytitle>journalctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>, + <citerefentry><refentrytitle>systemd-notify</refentrytitle><manvolnum>1</manvolnum></citerefentry>, + <citerefentry><refentrytitle>daemon</refentrytitle><manvolnum>7</manvolnum></citerefentry>, + <citerefentry><refentrytitle>sd-daemon</refentrytitle><manvolnum>3</manvolnum></citerefentry>, + <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>, + <citerefentry><refentrytitle>systemd.special</refentrytitle><manvolnum>5</manvolnum></citerefentry>, + <citerefentry project='die-net'><refentrytitle>pkg-config</refentrytitle><manvolnum>1</manvolnum></citerefentry>, + <citerefentry><refentrytitle>kernel-command-line</refentrytitle><manvolnum>7</manvolnum></citerefentry>, + <citerefentry project='man-pages'><refentrytitle>bootup</refentrytitle><manvolnum>7</manvolnum></citerefentry>, + <citerefentry><refentrytitle>systemd.directives</refentrytitle><manvolnum>7</manvolnum></citerefentry> + </para> + </refsect1> + +</refentry> |