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Diffstat (limited to 'man/systemd.xml')
| -rw-r--r-- | man/systemd.xml | 60 |
1 files changed, 59 insertions, 1 deletions
diff --git a/man/systemd.xml b/man/systemd.xml index 007705e494..b4a7e3ec93 100644 --- a/man/systemd.xml +++ b/man/systemd.xml @@ -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> |