[Bug 118882] [wishlist] sysrq enhancements (more actions)

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Summary:

Alt-SysRQ-[X]  functions are extremely useful, however they are
sometimes insufficient. I'd like to add a few more options, either pre-
defined, or user-configurable.

Motivation:

I have several times encountered serious problems that could be
repaired, without serious dataloss, but where I ended up having to reset
the computer, because there was no way to get an emergency root login.
This enhancement would solve that problem; it might also be rather
useful for getting / saving diagnostics.  Examples where this would be
useful:

 * Xserver crash (eg the wretched fglrx) going to 100% CPU.  We could
then  a)do some diagnostics on the hung process. b)shut down relatively
gracefully  c)try to save data where possible, for example  killing
emacs would make it autosave, and cat /dev/mem > memdump.dat   would
give us some hope later of retrieving the long email we were in the
middle of writing.

* Runaway processes eg a "fork bomb" or something which is rapidly leaking memory could be terminated. Likewise, anything that is using up so much I/O that it takes ages to actually start the root shell.
  
* Failing disk: one part of the drive becomes inaccessible because it is failing; but because you can't kill the process accessing that bit, the disk effectively blocks. And there's no way to take control of the system, and attempt a (partial) recovery, even though this is usually possible in principle.

Details:

I propose patching the kernel sysrq function to add some extra keys (in addition to the rather useful RSEIUB etc). These would be bound to user-definable actions. The one I really want to see is:
   killall -STOP  <all userspace processes, including the X-server>
   chvt 1   (and clear the screen)
   prompt for root password 
   start bash, at nice -10.

What I suggest is similar in principle to Alt-SysRQ-K, but less destructive.  There are some potential security risks here, but nothing that can't be fixed.  
If people think this is a good idea, I'll write a detailed proposal sadly kernel hacking is beyond me!

** Affects: linux-meta (Ubuntu)
     Importance: Wishlist
         Status: Confirmed


** Tags: wishlist
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[wishlist] sysrq enhancements (more actions)
https://bugs.launchpad.net/bugs/118882
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