Rebooting Via Proc and the magic sysreq key
You know what the best way to start the day is? I’m pretty sure that it doesn’t include a production web server putting its file systems in to read only mode. When this happens most local commands don’t work - init, shutdown, telnit and reboot all stop being useful and you have to resort to desperate measures… and here’s the desperate measure of the day.
First, check that your system supports the magic sysreq key -
$ cat /proc/sys/kernel/sysrq 1 # nonzero is good
Now you know you have the power to destroy your system through a single incorrect character, have a look at the Redhat Sysrq command reference (you want the ‘sysrq’ section). We tried to make it sync the disks and reboot - your requirements may vary.
root@web02:~# echo s > /proc/sysrq-trigger root@web02:~# echo b > /proc/sysrq-trigger # machine reboots
As techniques go this one’s a little obscure but it’s very useful in the right circumstances.