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

[Randy Dunlap <rdunlap@xenotime.net>]

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...


> >>> Once upon a time there was KeyboardRequest, which would send a SIGWINCH
> >>> to PID 1 (when pressing Alt-UP_arrow?).  I don't see any sign of this
> >>> feature in Linux 2.6.32 though.
> >>
> >> I couldn't find it in 2.4.37 either.
> >>
> >> Can 'loadkeys' help you any?
> >>
> >>> Looking at the Sysrq handlers in the kernel I don't see any keystrokes
> >>> that send SIGINT to PID 1 either.
> >>>
> >>> So, I'm wondering if it makes sense to add a Sysrq key to send a signal
> >>> to PID1 ?
> >>
> >> Dmitry, any ideas?
> >
> > We have SysRq bindings to unmount filesystems and reboot, isn't that
> > enough?
> 
> Reboot isn't clean... it doesn't signal MD-raid to "unmount" does it? 
> SysRq powerOff does cleanly shutdown md-raid, but who will drive to the 
> datacenter to press the power button to turn it back on?
> 
> I guess there are two ways to achieve clean (md-raid) reboot when using 
> serial console... a new SysRq to reboot "clean", or a new SysRq to 
> signal init.  Looking at ctrlaltdel(8), perhaps it could just one SysRq, 
> and let userspace (/sbin/init) configure it as needed.
> 
> 
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---
~Randy
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