Re: What interrupt does Ctrl+Alt+Delete send PID1?

From: Laurent Bercot <>
Date: Fri, 12 Jun 2015 02:35:28 +0200

On 12/06/2015 01:10, post-sysv wrote:
> Not sure what you meant by this statement, but you certainly can
> provided PID1 has set explicit signal handlers.

  Then it changed at some point. (I just tested to be sure, and I was
able to send a signal to my pid 1 indeed, on Linux 3.19.1.)

  There was a time where the kernel protected pid 1 against signals
sent by user processes, and only sent it signals it generated itself
such as SIGINT for Ctrl-Alt-Del. This is the reason why sysvinit
uses /dev/initctl as a communication point between init and the
"shutdown" program.

  Of course, POSIX being POSIX, the correct behaviour is completely
unspecified and left to the implementation, and Linux being Linux,
the change is completely undocumented.

Received on Fri Jun 12 2015 - 00:35:28 UTC

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