wiki:skinny_elephants_recovery

Version 6 (modified by Daniel Kahn Gillmor, 12 years ago) (diff)

added notes about domU updates

How do I reboot a server via the console?

If a server fails and you are not able to secure shell to investigate and fix the problem, the first step is to attempt to access the server via it's dom0 (if the server is a domU). Check our server overview page to see if the server in question is a domU and if so which dom0 it belongs to.

If the server in question is a stand alone server or a dom0 then it should be accessible via the serial console. The console should provide information about the crash. You can reboot the server by using the raising skinny elephants trick.

For machines with a console provided via [deb:cereal], you need to use special break characters. The exact sequence is:

ctrl-\ b r
ctrl-\ b s
ctrl-\ b e
ctrl-\ b i
ctrl-\ b u
ctrl-\ b b

For Xen domU's, you need to use ctrl-o (that's an "oh", not a "zero") to simulate the break character, so that makes it:

ctrl-o r
ctrl-o s
ctrl-o e
ctrl-o i
ctrl-o u
ctrl-o b

After each line you should get confirmation on screen that it was run, for example:

SysRq : Keyboard mode set to XLATE
SysRq : Emergency Sync
Emergency Sync complete
SysRq : Terminate All Tasks
SysRq : Kill All Tasks
SysRq : Emergency Remount R/O