Re:Early Linux filesystem reliability
by mschuster91 on Tuesday May 30, 2017 @05:05PM
(#14448538)
Nice to learn this - but how does one send a "break-u" e.g. from inside minicom, or in KVM virtual machines, via virsh console?
Re:Early Linux filesystem reliability
by throwaway76543 on Tuesday May 30, 2017 @06:04PM
(#14448918)
I usually use `cu`, but the docs for minicom tell me it's control-A followed by F to send a break signal. Then just hit "u." There are a number of single characters following a break with actions to them, the full doc on this kernel feature is here: https://www.kernel.org/doc/Documentation/admin-guide/sysrq.r...
I'm not terribly familiar with KVM but the VM console tools probably have some way to generate a break signal. Check the docs for how to "send a break."
Oh, and don't forget to enable this feature via sysctl -- per the above linux doc.
"Once filesystems are mounted read-only you can safely power off the machine."
In Ubuntu/Kubuntu there was once a key combination to forcefully unmount all file systems. THey seemed to have discontinued this? No?
You are looking for the Magic SysRq Key: https://en.wikipedia.org/wiki/Magic_SysRq_key
- Alt+SysRq+u remounts all filesystems readonly.
Looks like some of the Magic SysRq Keys are disabled by default now in new Ubuntus.
Filesystems can be remounted read-only via the serial console as well, with a break-u. Useful even when userland is otherwise inaccessible such as in the event of a fork bomb.