device: do not merge devices

[elogind.git] / man / systemd.xml

diff --git a/man/systemd.xml b/man/systemd.xml
index e74d71b126f096a2fd78c404f8e271841ec97da1..c027b4f6600fb46d1011a3c29cd18ff12b625988 100644 (file)
--- a/man/systemd.xml
+++ b/man/systemd.xml
@@ -141,7 +141,7 @@
                                 <listitem><para>Tell systemd to run a
                                 system instance (resp. session
                                 instance), even if the process ID is
                                 <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. system is not
+                                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
                                 (resp. is) run as init process.
                                 Normally it should not be necessary to
                                 pass these options, as systemd


@@ -226,18 +226,29 @@
                 <para>systemd provides a dependency system between
                 various entities called "units". Units encapsulate
                 various objects that are relevant for system boot-up
                 <para>systemd provides a dependency system between
                 various entities called "units". Units encapsulate
                 various objects that are relevant for system boot-up

-                and maintainance. The majority of units are configured
+                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
                 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), or inactive (meaning
-                stopped, unbound, unplugged, ...), as well as in the
-                process of being activated or deactivated,
-                i.e. between the two states. The following unit types
-                are available:</para>
+                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
 
                 <orderedlist>
                         <listitem><para>Service units, which control


@@ -304,6 +315,35 @@
                 list you may find in
                 <citerefentry><refentrytitle>systemd.special</refentrytitle><manvolnum>7</manvolnum></citerefentry>.</para>
 
                 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
                 <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