Linux kernel action upon init process exiting

Question

Say I am writing my own init program running on a Linux kernel.

What happens when my init program exits with return value 0 ?

Additionally is the behaviour different if the return value is non-zero?

JdeBP · Accepted Answer · 2015-04-13 14:50:51Z

6

What happens when my init program exits with return value 0?

This code, from the find_child_reaper function in kernel/exit.c, is run:

panic("Attempted to kill init! exitcode=0x%08x\n",
       father->signal->group_exit_code ?: father->exit_code);

And consequently this message appears on your console:

Kernel panic - not syncing: Attempted to kill init! exitcode=0x00000000

answered Apr 13, 2015 at 14:50

JdeBP

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Thank you! I misunderstood the message, and was thinking this is the kernel panic you will get if you try to send a kill signal to init, not the action performed if init just returns.
– Bjarke Freund-Hansen
Apr 28, 2015 at 9:13
2

@BjarkeFreund-Hansen There is no such thing as "just returns" for a process. When you return from main in a C program, you return to a stub function in the C library that then invokes a system call to end the process, just as if you called exit().
– DepressedDaniel
Mar 21, 2017 at 22:54
1

@DepressedDaniel: Thank you, that broadens my understanding. :)
– Bjarke Freund-Hansen
Mar 29, 2017 at 8:04
1

Wow! The crap you learn just passing through is amazing.
– Bruno Bronosky
Mar 5, 2018 at 18:57
1

If someone is wondering what the ?: means, look here: stackoverflow.com/a/3319144. In summary: the syntax x ?: y is a nonstandard GCC extension and is equivalent to x ? x : y.
– jp48
Aug 6, 2019 at 20:13

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