linux-kernel - Re: signal to PID 1 from serial console like KeyboardRequest or CAD

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Message-ID: <20110401155938.GA9163@core.coreip.homeip.net>
Date:	Fri, 1 Apr 2011 08:59:38 -0700
From:	Dmitry Torokhov <dmitry.torokhov@...il.com>
To:	Jeremy Jackson <jerj@...lanar.net>
Cc:	Randy Dunlap <rdunlap@...otime.net>, linux-kernel@...r.kernel.org
Subject: Re: signal to PID 1 from serial console like KeyboardRequest or CAD

On Fri, Apr 01, 2011 at 11:47:10AM -0400, Jeremy Jackson wrote:
> On 04/01/2011 11:42 AM, Randy Dunlap wrote:
> >On Fri, 01 Apr 2011 11:39:28 -0400 Jeremy Jackson wrote:
> >
> >>On 04/01/2011 01:37 AM, Dmitry Torokhov wrote:
> >>>On Thu, Mar 31, 2011 at 12:57:06PM -0700, Randy Dunlap wrote:
> >>>>On Fri, 25 Mar 2011 13:41:40 -0400 Jeremy Jackson wrote:
> >>>>
> >>>>>Hi,
> >>>>>
> >>>>>Sent to linux-console with no reply for over a week...
> >>>>>
> >>>>>I ran into a problem recently on a Linux server with a remote serial
> >>>>>console.  /sbin/init (actually Upstart) was in a state where nothing
> >>>>>(useful) was running.  I had to power cycle the machine to get back to
> >>>>>the boot prompt.  This has the side-effect of triggering raid rebuilds.
> >>>>>
> >>>>>It would be nice to have what Ctrl-Alt-Del does at the VGA console with
> >>>>>PS/2 or USB keyboard. This sends a SIGINT to PID 1, and most distros
> >>>>>have this set to do "shutdown -r now" which attempts a clean reboot.
> >>>>
> >>>>so C_A_D works at console via PS/2 or USB keyboard, but not on a remote
> >>>>serial console?  Could it be an issue with whatever remote/serial software
> >>>>you are using?
> >>>
> >>>I believe it is simply a matter of console keymap and assigning "boot"
> >>>value to the desired combination.
> >>
> >>The VGA console/keyboard isn't an issue here, C_A_D works great.  The
> >>problem is, that functionality isn't available when using *serial* console.
> >
> >That's why I asked whether it could be an issue with the serial interface
> >software.  E.g., minicom handles/processes certain keystrokes, other apps do things
> >differently, etc...
> 
> OK I guess I should clarify... when using Linux serial console, you
> can send BREAK <letter> to use SysRq functions.

Ah, right, we hardwire BREAK to SysRq when using serial console...

>  In minicom, META-F
> sends break.  This works fine for all the existing functions linux
> offers, r = reboot immediate, i = kill all tasks, etc.  But, there
> is no function available to reboot *clean*, or to signal PID 1
> (/sbin/init) to do same.  So, minicom is working/configured
> properly, Linux just doesn't offer a feature similar to C_A_D via
> serial.

SysRQ+REISUB should do it I think.

-- 
Dmitry
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