Re: Emergency shutdown feature - already solved, see magic sysrq

Pavel Machek (
Sat, 20 Dec 1997 14:32:37 +0100


> and init can react to key combinations too. The problem is that these are
> user processes, and they won't get a chance when the scheduler is hosed.
> (Which can happen with such trivial mistakes as a process running SCHED_RR
> in an endless loop.) An emergency reboot like this has to be in the kernel,
> called from some interrupt.

This is all done, look at magic sysrq (standart feature in 2.1.X kernels).

> I sometimes wanted a simple emergency reboot activated over the network.
> This would supposedly be rather easy to implement. I'm thinking about the
> following: a datagram has to be received (via IP is most convenient I think)
> with a special type which contains e.g. the target host name and current
> system time in 10 seconds granularity (to allow for clock fuzz) signed with
> a secret key (MD5 suffices). The feature is activated by writing this key
> into a /proc/sys entry. The cryptographic setup is to prevent trivial DOS
> attacks, and this way the feature has to be activated explicitly.

Hmm. I was also thinking on making magic sysrq work over the
network. Trouble is, how to do it securely. This looks nearly like

(mj: any comments?)


I'm really 	   Pavel
Look at ;-).