Non keyboard trigger of Alt-SysRQ-S-U-B

Is there any way that this can be triggered remotely? I frequently get into situations with a particular machine where 'reboot' or 'reboot -f' just plain won't work, and would like to be able do a 'filesystem clean' forcible reboot, but don't particularly care about services being shut down cleanly. Of course, the key is, I'm not at the keyboard of the server in question.

I figured there may be some way to have a module do this, but if anyone has any ideas, I'd appreciate it. I did see the example sent not too long ago about triggering a panic, but that won't cleanly unmount the filesystems.

-- Nathan

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Nathan Neulinger EMail: [email protected]
University of Missouri - Rolla Phone: (573) 341-4841
CIS - Systems Programming Fax: (573) 341-4216

If you have a serial console on the server, you can get sysrq by sending a serial break followed by the character. See drivers/char/serial.c on any 2.4 kernel. Otherwise you could hack up a module that calls handle_sysrq() directly. Unless you are sending a character that needs regs ('p'), kbd ('r') or tty ('k'), you can set those parameters to NULL. Any unrecognised character will try to use kbd and tty parameters.

Hi,

i've tried it with minicom and functioned : ctrl+a+F and key for function as in normal sysrq.

This approach will probably not help you a lot thought, since you wouldn't have access to your serial console too.

If you don't get your problems solved till now, i could make a simple single-purpos module which will export a syscall to priviledged process to call sysrq functions.

Gonna to have a look...

Bye B.

Hi Nathan,

I've just made an experimental module which offers syscall to privileged process, which internally translates itself into real sysrq handler (handle_sysrq) defined in drivers/char/sysrq.c. It occupates itself one of unussed linux system calls (concretely stty - no. 31). Makefile and patch for that sysrq.c are included in attached archive. (I stronly believe i didn't made it reversed :).
The patch itself only exports 1 variable and 1 function from sysrq.c, that normally aren't.

You can make a daemon, which listens on socket and triggers commands send by clients. Dont call sysrq+boot until a while needed to sync and unmount. This check, if sync and/or umount were finished before boot, should be really done, but it would require more changes in kernel source. And of course, the security is to be taken in client/server into account.

Bye B.