Subject: bug#12478: cat SEGV when I press Ctrl-Alt-SysRq-1 on text console

From: "Alan Curry" <[email-masked]>
Date: Thu, 20 Sep 2012 14:50:02 -0500 (GMT+5)

Rafal W. writes:
> 
> > $ cat /dev/zero
> > ^\Quit (core dumped)
> >
> > Steps to reproduce:
> > 1. Switch to any text console (it doesn't happen in X).
> > 2. Login
> > 3. Run: cat /dev/zero
> > 4. Press: Ctrl-Alt-SysRq-1 (or any number except letters:)

What's that supposed to do? Ctrl isn't normally used with SysRq.

> > 5. You'll see: ^\Quit (core dumped)

The ^\ character generates a QUIT signal (the same way ^C generates INT), and
death with core dump is the default response to SIGQUIT. Ctrl-4 is an
alternate way of typing Ctrl-\ so this is all perfectly normal for a key
combination involving Ctrl and 4.

By adding SysRq into the mix I don't know what exactly you accomplished.
Maybe you confused the keyboard. Most keyboards don't have every key wired
separately, and weird combinations can send events for keys that weren't
pressed.

To investigate further, try running 'stty -isig' to disable signal
generation, then 'cat >/dev/null' or maybe 'od -c' and type your key
combinations. Ctrl-D should still work for EOF to get you out, which is not a
signal so it's not disabled by stty -isig.