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SubjectRe: Forcing an immediate reboot
Anton Altaparmakov wrote:
> On Sat, 15 Oct 2005, Coywolf Qi Hunt wrote:
>
>>On 10/15/05, Anton Altaparmakov <aia21@cam.ac.uk> wrote:
>>
>>>echo s > /proc/sysrq-trigger
>>>echo u > /proc/sysre-trigger
>>>echo s > /proc/sysrq-trigger
>>
>>What the purpose of the second sync?
>
>
> Allows any i/o initiated between the first sync and the remount r/o to
> complete. Remember that r/o mounting doesn't stop i/o. It only stops you
> from writing to the fs at the vfs layer. Once a write/modification has
> entered the fs driver it will get written no matter what, unless the
> "reboot" sysrq is triggered in which case the kernel just reboots
> immediately.
>
> Maybe it is just paranoia on my part but I have gotten used to hitting
> Alt+PrtScr+S, +U, +S, +B so I do it automatically.

Second sync is a must, otherwise remounting read-only is not written to
the filesystem (at least in my case) so no fsck is saved. But you can
save first sync (before remount), and then you get nice sequence which
even admins comming from Windows can remember - they have to use USB to
safely reboot their Linux systems ;-) (alt-sysrq-U, S, B)
Petr

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