Difference between /etc/init.d/ and innitab

newbie14 · 05-16-2012, 02:07 AM

Dear All,
I am confuse where some programme start with /etc/init.d/ and some start in inittab and some what the /etc/init.d/rc. From what I understand inittab is for the on boot process to start automatically is it?

acid_kewpie · 05-16-2012, 03:11 AM

inittab defines, amongst a few other things like starting console processes, what the runlevel is, and once the runlevel is defined, the scripts in /etc/rc.d/, which are symlinks onto the /etc/init.d scripts are executed accordingly. (Well, for sysVinit at least, changed somewhat for systemd and other newer systems, but the principle still holds)

newbie14 · 05-16-2012, 04:12 AM

Dear Kewpie,
So when the system load it will first look into inittab is it? So in inittab you do find configuration files for other or just console processes? Are these proceses also link to /etc/init.d? I notice some services are run as /etc/init.d/service start ( this will run only if there is a file in /etc/init.d right? Then some are run on inittab what is their difference?

acid_kewpie · 05-16-2012, 05:00 AM

just LOOK at the inittab file:

Code:

id:3:initdefault:

# System initialization.
si::sysinit:/etc/rc.d/rc.sysinit

l0:0:wait:/etc/rc.d/rc 0
l1:1:wait:/etc/rc.d/rc 1
l2:2:wait:/etc/rc.d/rc 2
l3:3:wait:/etc/rc.d/rc 3
l4:4:wait:/etc/rc.d/rc 4
l5:5:wait:/etc/rc.d/rc 5
l6:6:wait:/etc/rc.d/rc 6

so if it's runlevel 3 go run the rc scripts for runelvel 3 and so on...

services don't run from inittab, it starts the process to run the services as a whole

newbie14 · 05-16-2012, 12:12 PM

Dear Kewpie,
This is what I see in my inittab. So it just have this id:3:initdefault: not pointing to any of the rc ? I dont quite get this "services don't run from inittab, it starts the process to run the services as a whole" Which process does it start? So when boot first it come to inittab is it?

Quote:

# inittab is only used by upstart for the default runlevel.
#
# ADDING OTHER CONFIGURATION HERE WILL HAVE NO EFFECT ON YOUR SYSTEM.
#
# System initialization is started by /etc/init/rcS.conf
#
# Individual runlevels are started by /etc/init/rc.conf
#
# Ctrl-Alt-Delete is handled by /etc/init/control-alt-delete.conf
#
# Terminal gettys are handled by /etc/init/tty.conf and /etc/init/serial.conf,
# with configuration in /etc/sysconfig/init.
#
# For information on how to write upstart event handlers, or how
# upstart works, see init(5), init(8), and initctl(8).
#
# Default runlevel. The runlevels used are:
# 0 - halt (Do NOT set initdefault to this)
# 1 - Single user mode
# 2 - Multiuser, without NFS (The same as 3, if you do not have networking)
# 3 - Full multiuser mode
# 4 - unused
# 5 - X11
# 6 - reboot (Do NOT set initdefault to this)
#
id:3:initdefault:

acid_kewpie · 05-16-2012, 01:46 PM

can I suggest you actually just READ those comments you pasted in? They are EXACTLY what you're asking about.

sundialsvcs · 05-16-2012, 05:09 PM

As previously noted: the inittab file is what is consulted ... and its contents are what point the system to the various directories and their contents.

The script /etc/rc.d/rc n is what does it.

newbie14 · 05-17-2012, 03:20 AM

Dear Sun,
If I read this "inittab is only used by upstart for the default runlevel.". So in this case it does not call the script /etc/rc.d/rc n am I right here? Thank you.

acid_kewpie · 05-17-2012, 03:26 AM

well seeing as there is literally no code in it to do anything other than set the runlevel... no.

newbie14 · 05-17-2012, 03:29 AM

Dear Kewpie,
So in this case who start the /etc/rc.d/rc n scripts then?

acid_kewpie · 05-17-2012, 03:30 AM

upstart, but I don't know how upstart itself starts. It'll be pretty straight forward I'm sure, I just don't know myself.

newbie14 · 05-17-2012, 03:31 AM

Dear Chris,
So I got it now this inittab starts the upstart and then that starts the rest of the script right. Never mind I will look further into upstart.

greatbear · 05-17-2012, 12:00 PM

Newbie14, the executable that actually starts rc.d/rc scripts is called Init. Init can be considered the 'Main' function in the linux kernel, because it is usually the very first program. Here is a wikipedia article about it. Init reads the innitab file, and then it proceeds to the other configuration files. It also starts up scripts which are processed by executing shell programs such as BASH, PERL and PYTHON.

newbie14 · 05-17-2012, 12:20 PM

Dear Great,
Thank you that is quite helpful to understand better about the process sequence.