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authorLennart Poettering <lennart@poettering.net>2010-07-06 03:46:31 +0200
committerLennart Poettering <lennart@poettering.net>2010-07-06 03:46:31 +0200
commit59a3e1bc46819d69df6353a86aa0e796cd821024 (patch)
treeaf431d2c8d0a40c56e2405cf599f6c5bb591359b /man/systemd.xml
parent99ffae46d38f05b6c8bc09fe29e50a507ae8b79b (diff)
man: more blurbs
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diff --git a/man/systemd.xml b/man/systemd.xml
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@@ -296,10 +296,68 @@
<citerefentry><refentrytitle>systemd.special</refentrytitle><manvolnum>7</manvolnum></citerefentry>
for details about these target units.</para>
+ <para>Processes systemd spawns ared 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 comaptibility implementations of the
+ various SysV client tools 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
- Announcement Document</ulink>.</para>
+ Design Document</ulink>.</para>
</refsect1>
<refsect1>