THE INIT PROCESS
1. The init process is the first non-kernel process that is started, and, therefore, it always gets the process ID number of 1.
2. init reads its configuration file, /etc/inittab, and determines the runlevel where it should start.
3. Essentially, a runlevel dictates the system’s behavior.
4. Each level (designated by an integer between 0 and 6) serves a specific purpose.
5. A runlevel of initdefault is selected if it exists; otherwise, you are prompted to supply a runlevel value.
Run Level ID
|
Description
|
0
|
Halt the system
|
1
|
Enter single-user mode
|
2
|
Multiuser mode, but without Network File System
(NFS)
|
3
|
Full multiuser mode (normal)
|
4
|
Unused
|
5
|
Same as runlevel 3, except using an X Window System
login rather than a text-based login
|
6
|
Reboot the system
|
6.
When it is told
to enter a runlevel, init executes a script, as dictated by the /etc/
inittab file.
7.
The default
runlevel that the system boots into is determined by the initdefault entry
in the /etc/inittab file.
If, for example, the entry in the file is :- id:3:initdefault:
--> This means that the system will boot into runlevel 3.
-->But if, on the other
hand, the entry in the file is id:5:initdefault:,
--> This means the system will
boot into runlevel 5, with the X Window subsystem running with a graphical
login screen.
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