Magic SysRq Key Sequences over Remote DRAC5 Connection

Robert Brockway robert at timetraveller.org
Thu Jun 3 21:45:05 CDT 2010


On Wed, 2 Jun 2010, Bryce Nesbitt wrote:

> These servers run Debian Linux, and we periodically have problems with out
> of control memory situations.  We could save servers from a hard reboot by
> sending Magic SysReq commands such as "m" and "f" (to dump Linux Kernel
> memory stats and invoke the Out of Memory Killer (oom-killer).  Or make a
> reboot nicer by syncing disks first.  These commands work fine directly from
> an attached keyboard (e.g. Alt-SysRq-m).  Can we get Magic SysRq over DRAC5?

Hi Bryce.  Do you mean in a situation in which a shell cannot be opened on 
the system?  /proc/sysrq-trigger can be used if you can open a shell as 
root (say over DRAC).  The WP article shows how to use sysrq-trigger. 
There are plenty of situations in which a shell can be opened but a 
normal reboot has become impossible - I often use sysrq-trigger in these 
situations.

The page below talks about how to use Magic Sysrq over a serial console.

http://tldp.org/HOWTO/Remote-Serial-Console-HOWTO/security-sysrq.html

Cheers,

Rob

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Email: robert at timetraveller.org		Linux counter ID #16440
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