Hardware Reference
In-Depth Information
Table 3-4.
telinit Run Levels
Level
Description
0-6
Run level 0, 1, 2, 3, 4, 5, or 6
a, b, c
Invoke inittab entries with a, b, or c
Q or q
Tell init to reexamine /etc/inittab
S or s
Change to single-user mode
U or u
Tell init to reexecute itself
Any unrecognized level is silently ignored.
Change of Run Level
Let's use an example to keep the references concrete. If you were in run level 1 and
directed the system to change to run level 2 with
# telinit 2
the following happens:
1.
/etc/init.d/rc
executes all
K*
(kill) scripts for run level
2
(the level you are changing to), with an argument of
stop
.
2.
/etc/init.d/rc
executes all
S*
(start) scripts for run level
2
,
with the argument
start
.
3.
Except where previously noted (redundant stop and start
script executions are omitted)
Another way to think about this is that all
K*
symlinks at a particular run level
identify services that
should not be running
at that level. Similarly, the
S*
symlinks
identify services that
should be running
at that level.
Single-User Mode
Changing to single-user mode works the same as for any other level, except that most of
the scripts are designed to be kill scripts to stop services (
/etc/rc1.d/K*
), rather than to
start them.
The concept of single-user mode is that only one user will be using the system,
without unnecessary services running in the background. This run level is normally used
to repair the file systems or to reconfigure the system.
