systemd
systemd is the init system and service manager used by openSUSE.
The program systemd is the process with process ID 1. It is responsible for initializing the system in the required way. systemd is started directly by the kernel and resists signal 9, which normally terminates processes. All other programs are either started directly by systemd or by one of its child processes.
Systemd is a replacement for the System V init daemon. systemd is fully compatible with System V init (by supporting init scripts). One of the main advantages of systemd is that it considerably speeds up boot time by aggressively paralleling service starts. Furthermore, systemd only starts a service when it is really needed. Daemons are not started unconditionally at boot time, but rather when being required for the first time. systemd also supports Kernel Control Groups (cgroups), snapshotting and restoring the system state and more. See http://www.freedesktop.org/wiki/Software/systemd/ for details.
see openSUSE:Systemd_tips and the openSUSE systemd documentation
Configuration
All systemd daemons including PID1 can have theirs default settings tuned. The way to configure these various daemons is similar and is described in the relevant man pages.
For example, for a detailed description of PID1 configuration, you can refer to systemd-system.conf(5) man page.
Main Configuration files
Each systemd daemon is accompanied with a main configuration file.
The shipped main configuration files show the default values set during compilation. They might be stored either in /usr/lib/systemd/ or in /etc/systemd/.
/usr/systemd/ will be overriden during updates anyways).Drop-in snippets
Drop-ins are configuration snippets and as already mentioned have higher precedence over main configuration files. They are usually stored in
/etc/systemd/*.conf.d/ for drop-ins belonging to sysadmins or installed in /usr/lib/systemd/*.conf.d/ by packages when downstream needs to customize specific parts of a configuration.
For example if a sysadmin wants to disable the rate limiting enforced by systemd-journald by default, he can run the following commands:
$ mkdir /etc/systemd/journald.conf.d $ cat >/etc/systemd/journald.conf.d/60-rate-limit.conf<<EOF # Disable rate limiting RateLimitIntervalSec=0 EOF $ systemctl restart systemd-journald
Getting a configuration overview
Since the configuration of a systemd component might be scattered into different places, it might be tricky to get a global overview.
Fortunately systemd-analyze cat-config can be used to inspect the configuration of one systemd component. For example to inspect the configuration files affecting systemd-journald, one can execute:
$ systemd-analyze cat-config systemd/journald.conf
See systemd-analyze(1) man page for more examples.
Avoiding drop-in conflicts
To avoid conflict between drop-ins shipped by downstream and those created by users, it is recommended to prefix all filenames in those sub-directories with a two-digit number and a dash, e.g. 60-rate-limit.conf.
Moreover by using a prefix number >= 50, users are guaranteed that theirs drop-in snippets won't be overridden by those shipped by downstream. Or to say this differently: the available user range is [50-99] while the range [0-49] is reserved for packages.
systemctl cat should be used instead of systemd-analyze cat-config.