When a linux computer is “hung” or “frozen” you can use a Magic
SysRq key sequence to
send various low level requests to the kernel in order to try to recover
from or investigate the problem. This is extremely useful when
troubleshooting server lockups, but until recently
libvirt did not expose this
functionality for
KVM
guests.
In v0.9.3 (and newer) of libvirt you can send a Magic SysRq sequence to
a guest by utilizing the send-key
subcommand provided by virsh
. In
other words, sending the ‘h’ Magic SysRq command is as simple as:
\
dustymabe@media: ~>virsh send-key guest1 KEY_LEFTALT KEY_SYSRQ KEY_H
After executing the command a help message will be printed to the
console of the guest known as guest1. Any other character can be sent
as well by substituting KEY_H
with KEY_X
, where X
is the character.
Happy Investigating!
Dusty