Take the 2-minute tour ×
Server Fault is a question and answer site for professional system and network administrators. It's 100% free, no registration required.

Please, I am not looking for a rehash of what's stated in RedHat's documentation regarding emergency mode. I would like to know what steps are involved from the time grub hands off to the kernel to the time you get a emergency mode login prompt.

I imagine /sbin/init is completely bypassed and therefore rc.sysinit bypassed as well. I don't however know what isn't bypassed or how emergency mode differs (intimately) with init=/bin/sh.

What sort of steps does the kernel take when given the emergency argument at boot time? Thanks!

share|improve this question
add comment

2 Answers 2

up vote 2 down vote accepted

Normal situation:

  1. bios initialization
  2. bootloader
  3. kernel initialization
  4. init starts and enters your runlevel & execute:
    • /etc/rc.d/rc.sysinit
    • /etc/rc.d/rc and /etc/rc.d/rc?.d/
    • /etc/rc.d/rc.local
  5. X display manager

In emergency mode you bypass 'rc.sysinit' and runs only 'sulogin' script by default. To see what is happening on your system see /etc/inittab.

share|improve this answer
    
That's mostly what I was looking for, now I know emergency mode is passed as an argument to /sbin/init. Thanks! What is the boot process when you pass init=/bin/sh to the kernel on boot? I imagine the kernel no longer calls /sbin/init and instead calls /bin/sh. Is this correct? –  CarpeNoctem Feb 16 '10 at 9:04
    
I tested my assumption regarding init=/bin/sh by passing init=/sbin/init. The system booted as normal so I imagine that init=/bin/sh does in fact cause the kernel to execute sh in place of init, versus as some sort of argument to init or something else. –  CarpeNoctem Feb 16 '10 at 9:09
    
Yes, one of last things kernel initialization does is invoke execve() on the argument you pass to it by init=whatever if it fails it tries to run init from several locations if that fails you end up with /bin/sh. –  fuo Feb 17 '10 at 4:41
add comment

No scripts are processed and you are given a root shell. Requires a password. Uses PAM if configured.

share|improve this answer
    
Not telling me anything I don't already know, but that doesn't make your answer any less correct. Thanks. –  CarpeNoctem Feb 16 '10 at 3:21
add comment

Your Answer

 
discard

By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.