On Tue 2019-09-03 18:08:40, Adam Borowski wrote: > This advice is obsolete and slightly harmful for filesystems from this > millenium: any modern filesystem can handle unexpected crashes without > requiring fsck -- and on the other hand, trying to write to the disk when > the kernel is in a bad state risks introducing corruption. Actually no, I don't think it is good idea. sync is still useful these days -- you want the current data to be written to disk; true, you'll not have to do fsck, but you may lose your current data. Best regards, Pavel > For ext2, any unsafe shutdown meant widespread breakage, but it's no longer > a reasonable filesystem for any non-special use. > > Signed-off-by: Adam Borowski <kilobyte@xxxxxxxxxx> > --- > Documentation/admin-guide/sysrq.rst | 20 +++++++++----------- > 1 file changed, 9 insertions(+), 11 deletions(-) > > diff --git a/Documentation/admin-guide/sysrq.rst b/Documentation/admin-guide/sysrq.rst > index 7b9035c01a2e..72b2cfb066f4 100644 > --- a/Documentation/admin-guide/sysrq.rst > +++ b/Documentation/admin-guide/sysrq.rst > @@ -171,22 +171,20 @@ It seems others find it useful as (System Attention Key) which is > useful when you want to exit a program that will not let you switch consoles. > (For example, X or a svgalib program.) > > -``reboot(b)`` is good when you're unable to shut down. But you should also > -``sync(s)`` and ``umount(u)`` first. > +``reboot(b)`` is good when you're unable to shut down, it is an equivalent > +of pressing the "reset" button. > > ``crash(c)`` can be used to manually trigger a crashdump when the system is hung. > Note that this just triggers a crash if there is no dump mechanism available. > > -``sync(s)`` is great when your system is locked up, it allows you to sync your > -disks and will certainly lessen the chance of data loss and fscking. Note > -that the sync hasn't taken place until you see the "OK" and "Done" appear > -on the screen. (If the kernel is really in strife, you may not ever get the > -OK or Done message...) > +``sync(s)`` is handy before yanking removable medium or after using a rescue > +shell that provides no graceful shutdown -- it will ensure your data is > +safely written to the disk. Note that the sync hasn't taken place until you see > +the "OK" and "Done" appear on the screen. > > -``umount(u)`` is basically useful in the same ways as ``sync(s)``. I generally > -``sync(s)``, ``umount(u)``, then ``reboot(b)`` when my system locks. It's saved > -me many a fsck. Again, the unmount (remount read-only) hasn't taken place until > -you see the "OK" and "Done" message appear on the screen. > +``umount(u)`` can be used to mark filesystems as properly unmounted. From the > +running system's point of view, they will be remounted read-only. The remount > +isn't complete until you see the "OK" and "Done" message appear on the screen. > > The loglevels ``0``-``9`` are useful when your console is being flooded with > kernel messages you do not want to see. Selecting ``0`` will prevent all but -- (english) http://www.livejournal.com/~pavelmachek (cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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