Re: Documentation for init

From: Austin S Hemmelgarn
Date: Tue Aug 26 2014 - 08:35:17 EST

On 2014-08-26 01:48, Shea Levy wrote:
> Hi all,
> Is there any official documentation of the init process? I'm
> specifically interested in the process state at kernel handoff (argv,
> envp, open fds, etc.) as well as any special properties pid 1 has
> (parent of all orphans, anything else?).
> Thanks,
> Shea Levy
> P.S. I am not subscribed to LKML, please CC me in responses
This is following is just my understanding based on what I have seen and
read, and I may well be totally wrong on some points (if that is the
case, I would love to know about it, I'm always trying to learn more).

As far as I can tell, the argv that gets passed to the init process is
the concatenation of all arguments on the kernel command-line that the
kernel doesn't recognize or parse. A lot of LiveCD's make use of this
to control hardware detection and module loading. The only open file
descriptors (i believe, I may be wrong) are 0, 1, and 2, all pointing at

As for special properties:
* Parent of all orphans
* Doesn't have a session ID until it calls setsid() (not certain about
this one)
* Calling exit() will cause either a reboot or possibly a panic (I
think that this is dependent on the argument passed to exit())
* Not catching a fatal signal will cause a panic (this means that
sending SIGKILL and SIGABRT to PID 1 will always cause a panic).
* Has a PPID of 0, only other process like this is kthreadd
* Becomes the parent of most X programs (almost all of them dissociate
very quickly from whatever started them.
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