INIT.D(7) The SuSE boot concept INIT.D(7)
INIT.D - The SuSE boot concept
The scripts for controlling the system are placed in /etc/init.d/ (they have been moved according to the Linux Standard Base (LSB) specifi-
cation). These scripts are executed directly or indirectly by /sbin/init, the father of all processes. The configuration of /sbin/init is
given by the file /etc/inittab (see inittab(5)).
At boot time, the boot level master script /etc/init.d/boot is called to initialise the system (e.g. file system check, ...). It also exe-
cutes some hardware init scripts linked into /etc/init.d/boot.d/. Then it calls /etc/init.d/boot.local, which executes the local commands.
After system startup, /sbin/init will normally switch on the default run level given in /etc/inittab. It calls the run level master script
/etc/init.d/rc to start or stop services provided by the other scripts under /etc/init.d/.
Both scripts, then boot level master script /etc/init.d/boot and the the run level master script /etc/init.d/rc starts all other boot or
runlevel scripts either sequential or partial parallel within their dependencies order.
To control the services of a run level, the corresponding scripts are linked into run level directories /etc/init.d/rc<X>.d/, where
<X>=0,1,2,3,4,5,6,S is the run level number.
There are two kinds of symbolic link: start links, which are called when entering a run level, and stop links, which are called when leav-
ing a run level. Note that each service in the run levels 2, 3, 4, and 5 consists of a start and a stop link. Within SuSE boot concept a
differential link scheme is used to be able to change a runlevel in comparision with the former level.
If parallel executing of the boot scripts is enabled (see /etc/sysconfig/boot variable RUN_PARALLEL) then both master scripts uses the pro-
gram startpar(8) which starts or stops multiple services in parallel. Startpar(8) will look for the files /etc/init.d/.depend.boot,
/etc/init.d/.depend.start, and /etc/init.d/.depend.stop to get the dependencies for each service. The files will be written, beside the
symbolic links in the boot and runlevel directories, by the program insserv(8).
To avoid redundant starts when changing run levels, only those services are started which have no start link in the previous run level.
And to avoid redundant stops when changing run levels, only those services are stopped which have no start link in the current level. To
control this behaviour, the names of the scripts are added on the names of the start and stop links.
To control the order of service starts and stops, the start and stop links include a number in their link name.
The system configuration files in /etc/sysconfig contain most of the variables used to configure the installed services. These variables
can easily be changed by YaST or by using an editor. After using an editor, the script /sbin/SuSEconfig must be called to distribute the
settings into the system.
The script /etc/init.d/lpd starts or stops the line printer daemon for the printing service, according to the flag used:
To do this automatically in run level 3, this script is linked into /etc/init.d/rc3.d/ with these two symbolic links
/etc/init.d/rc3.d/S20lpd -> ../lpd
/etc/init.d/rc3.d/K20lpd -> ../lpd
The corresponding link with the letter S is used to start a service. For the printing service the number between the letter S and the name
should be greater than the number of the start link of the network service. The corresponding link with the letter K is used to stop a
service. The number of the stop link for the printing service should be less than that of the stop link for the network service so that the
printer daemon is stopped before shutting down the network service.
Run levels and their services
0 This level is used for halting the system. The only valid service for this level is the script halt, which is linked into
/etc/init.d/rc0.d/. The script halt executes /etc/init.d/halt.local. Special system issues for halt or reboot should be added
6 This level is used for rebooting the system. The only valid service for this level is the script reboot, which is linked into
/etc/init.d/rc6.d/. The script reboot executes /etc/init.d/halt.local. Specials system issues for halt or reboot should be added
S This mode is used to switch from boot phase into single user mode. The last valid service for this mode is the script single, which
is linked into /etc/init.d/rcS.d/. In this mode you have only one console.
1 According to the Linux Standard Base (LSB) specification this runlevel is used to switch from normal runlevel into single user mode.
This is different from former SuSE Linux versions!
2 The run level 2 is without remote networking. Note that on some other systems this is identical with the single user mode. This run
level can have more than one virtual console.
3 The run level 3 is with network. This run level is for server stations not automatically running X.
5 The level 5 is with network and xdm(1). You should have a configured and perfectly running X Window System for this work station
4 The run level 4 is not (yet) used.
This script is a model for writing your own. You can use insserv(8) to include your own script into a run level.
insserv(8), startpar(8), init(8), inittab(5), and the SuSE Linux handbook, chapter The SuSE boot concept.
1996-2005 SuSE Linux AG, Nuernberg, Germany.
Florian La Roche <http://www.suse.de/feedback>, Werner Fink <firstname.lastname@example.org>, Burchard Steinbild <http://www.suse.de/feedback>.
4.4 Berkeley Distribution Nov 15, 2000 INIT.D(7)