<para>systemd is a system and session manager for
Linux operating systems. When run as first process on
- boot (as PID 1) it may act as init system that brings
- up and maintains userspace.</para>
+ 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
+ <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
+ 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 system instance, systemd interprets
+ the configuration file
+ <filename>system.conf</filename>, otherwise
+ <filename>session.conf</filename>. See
+ <citerefentry><refentrytitle>systemd.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>
+ for more information.</para>
</refsect1>
<refsect1>
<listitem><para>Prints a short help
text and exits.</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>--running-as=</option></term>
-
- <listitem><para>Tell systemd to run in
- a particular mode. Argument is one of
- <option>system</option>,
- <option>session</option>. Normally it
- should not be necessary to pass this
- option, as systemd automatically
- detects the mode it is started
- in. This call is hence of little use
- except for
- debugging.</para></listitem>
- </varlistentry>
<varlistentry>
<term><option>--test</option></term>
configuration items understood in unit
definition files.</para></listitem>
</varlistentry>
- <varlistentry>
- <term><option>--confirm-spawn</option></term>
-
- <listitem><para>Ask for confirmation when spawning processes.</para></listitem>
- </varlistentry>
<varlistentry>
<term><option>--introspect=</option></term>
<listitem><para>Extract D-Bus
interface introspection data. This is
- mostly useful at build at install time
+ mostly useful at install time
to generate data suitable for the
D-Bus interfaces
repository. Optionally the interface
name for the introspection data may be
- specified. If omitted the
+ specified. If omitted, the
introspection data for all interfaces
is dumped.</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>--session</option></term>
+
+ <listitem><para>Tell systemd to run a
+ system instance (resp. session
+ instance), even if the process ID is
+ not 1 (resp. is 1), i.e. systemd is not
+ (resp. is) run as init process.
+ 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.</para></listitem>
+ </varlistentry>
+ <varlistentry>
+ <term><option>--dump-core</option></term>
+
+ <listitem><para>Dump core on crash. This switch has no effect when run as session instance.</para></listitem>
+ </varlistentry>
+ <varlistentry>
+ <term><option>--crash-shell</option></term>
+
+ <listitem><para>Run shell on crash. This switch has no effect when run as session instance.</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 session instance.</para></listitem>
+ </varlistentry>
+ <varlistentry>
+ <term><option>--show-status=</option></term>
+
+ <listitem><para>Show terse service
+ status information while booting. This
+ switch has no effect when run as
+ session instance. Takes a boolean
+ argument which may be omitted
+ which is interpreted as
+ <option>true</option>.</para></listitem>
+ </varlistentry>
+ <varlistentry>
+ <term><option>--sysv-console=</option></term>
+
+ <listitem><para>Controls whether
+ output of SysV init scripts will be
+ directed to the console. This switch
+ has no effect when run as session
+ instance. Takes a boolean argument
+ which may be omitted which is
+ interpreted as
+ <option>true</option>.</para></listitem>
+ </varlistentry>
+ <varlistentry>
+ <term><option>--log-target=</option></term>
+
+ <listitem><para>Set log
+ target. Argument must be one of
+ <option>console</option>,
+ <option>syslog</option>,
+ <option>kmsg</option>,
+ <option>syslog-or-kmsg</option>,
+ <option>null</option>.</para></listitem>
+ </varlistentry>
<varlistentry>
<term><option>--log-level=</option></term>
<option>info</option>,
<option>debug</option>.</para></listitem>
</varlistentry>
- <varlistentry>
- <term><option>--log-target=</option></term>
-
- <listitem><para>Set log
- target. Argument must be one of
- <option>console</option>,
- <option>syslog</option>,
- <option>kmsg</option>,
- <option>syslog-or-kmsg</option>,
- <option>null</option>.</para></listitem>
- </varlistentry>
<varlistentry>
<term><option>--log-color=</option></term>
</variablelist>
</refsect1>
+ <refsect1>
+ <title>Concepts</title>
+
+ <para>systemd provides a dependency system between
+ various entities called "units". 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 or dynamically from system state. 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
+ 'maintenance' 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, or an operation timed out). 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 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>Snapshot units can be used to
+ temporarily save the state of the set of
+ systemd units, which later may be restored by
+ activating the saved snapshot unit. For more
+ information see
+ <citerefentry><refentrytitle>systemd.snapshot</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 encapsulated memory swap
+ partitions or files of the operating
+ systemd. 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>
+
+ </orderedlist>
+
+ <para>Units are named as their configuration
+ files. Some units have special semantics. A detailed
+ list you may find 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 requests 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>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="http://www.kernel.org/doc/Documentation/cgroups/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>/cgroup/systemd/</filename>), or in tools
+ such as
+ <citerefentry><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>Systemd contains native implementations of
+ various tasks that need to be executed as part of the
+ boot process. For example, it sets the host name 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>
+ </refsect1>
+
<refsect1>
<title>Directories</title>
--variable=systemdsystemconfdir</command>
returns the path of the system
configuration directory. Packages
- should alter this directory only with
+ should alter the content of these
+ directories only with the
+ <command>enable</command> and
+ <command>disable</command> commands of
the
- <citerefentry><refentrytitle>systemd-install</refentrytitle><manvolnum>1</manvolnum></citerefentry>
+ <citerefentry><refentrytitle>systemctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>
tool.</para></listitem>
</varlistentry>
</variablelist>
unit files in the directory returned
by <command>pkg-config systemd
--variable=systemdsessionunitdir</command>. Global
- configuration is done in the
- directory reported by
- <command>pkg-config systemd
+ configuration is done in the directory
+ reported by <command>pkg-config
+ systemd
--variable=systemdsessionconfdir</command>. The
- <citerefentry><refentrytitle>systemd-install</refentrytitle><manvolnum>1</manvolnum></citerefentry>
+ <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
SysV init script directory varies
between distributions. If systemd
cannot find a native unit file for a
- requested service it will look for a
+ requested service, it will look for a
SysV init script of the same name
(with the
<filename>.service</filename> suffix
when figuring out whether a service
shall be enabled. Note that a service
unit with a native unit configuration
- file can be started by activating it
+ file cannot be started by activating it
in the SysV runlevel link
farm.</para></listitem>
</varlistentry>
</variablelist>
</refsect1>
+ <refsect1>
+ <title>Kernel Command Line</title>
+
+ <para>When run as system instance systemd parses a few kernel command line arguments:</para>
+
+ <variablelist>
+ <varlistentry>
+ <term><varname>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.</para></listitem>
+ </varlistentry>
+
+ <varlistentry>
+ <term><varname>systemd.dump_core=</varname></term>
+
+ <listitem><para>Takes a boolean
+ argument. If <option>true</option>
+ systemd dumps core when it
+ crashes. Otherwise no core dump is
+ created. Defaults to
+ <option>true</option>.</para></listitem>
+ </varlistentry>
+
+ <varlistentry>
+ <term><varname>systemd.crash_shell=</varname></term>
+
+ <listitem><para>Takes a boolean
+ argument. If <option>true</option>
+ systemd spawns a shell when it
+ crashes. Otherwise no core dump is
+ created. Defaults to
+ <option>false</option>, for security
+ reasons, as the shell is not protected
+ by any password
+ authentication.</para></listitem>
+ </varlistentry>
+
+ <varlistentry>
+ <term><varname>systemd.crash_chvt=</varname></term>
+
+ <listitem><para>Takes an integer
+ argument. If positive systemd
+ activates the specified virtual
+ terminal when it crashes. Defaults to
+ <literal>-1</literal>.</para></listitem>
+ </varlistentry>
+
+ <varlistentry>
+ <term><varname>systemd.confirm_spawn=</varname></term>
+
+ <listitem><para>Takes a boolean
+ argument. If <option>true</option>
+ asks for confirmation when spawning
+ processes. Defaults to
+ <option>false</option>.</para></listitem>
+ </varlistentry>
+
+ <varlistentry>
+ <term><varname>systemd.show_status=</varname></term>
+
+ <listitem><para>Takes a boolean
+ argument. If <option>true</option>
+ shows terse service status updates on
+ the console during bootup. Defaults to
+ <option>true</option>.</para></listitem>
+ </varlistentry>
+
+ <varlistentry>
+ <term><varname>systemd.sysv_console=</varname></term>
+
+ <listitem><para>Takes a boolean
+ argument. If <option>true</option>
+ output of SysV init scripts will be
+ directed to the console. Defaults to
+ <option>true</option>, unless
+ <option>quiet</option> is passed as
+ kernel command line option in which
+ case it defaults to
+ <option>false</option>.</para></listitem>
+ </varlistentry>
+
+ <varlistentry>
+ <term><varname>systemd.log_target=</varname></term>
+ <term><varname>systemd.log_level=</varname></term>
+ <term><varname>systemd.log_color=</varname></term>
+ <term><varname>systemd.log_location=</varname></term>
+
+ <listitem><para>Controls log output,
+ with the same effect as the
+ <varname>$SYSTEMD_LOG_TARGET</varname>, <varname>$SYSTEMD_LOG_LEVEL</varname>, <varname>$SYSTEMD_LOG_COLOR</varname>, <varname>$SYSTEMD_LOG_LOCATION</varname>
+ environment variables described above.</para></listitem>
+ </varlistentry>
+
+ </variablelist>
+ </refsect1>
+
<refsect1>
<title>Sockets and FIFOs</title>
abstract namespace.</para></listitem>
</varlistentry>
+ <varlistentry>
+ <term><filename>@/org/freedesktop/systemd1/shutdown</filename></term>
+
+ <listitem><para>Used internally by the
+ <citerefentry><refentrytitle>shutdown</refentrytitle><manvolnum>8</manvolnum></citerefentry>
+ tool to implement delayed
+ shutdowns. This is an AF_UNIX datagram
+ socket in the Linux abstract
+ namespace.</para></listitem>
+ </varlistentry>
+
<varlistentry>
<term><filename>@/org/freedesktop/systemd1/private</filename></term>
<para>
<citerefentry><refentrytitle>systemctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
<citerefentry><refentrytitle>systemadm</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
- <citerefentry><refentrytitle>systemd-install</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>7</manvolnum></citerefentry>,
~ianmdlvl / elogind.git / blobdiff