Automatic fsck

[Lars Wirzenius]

ti, 2008-08-12 kello 20:57 +1000, Ian Chennell kirjoitti:
> If fsck is to run during shutdown, then there definitely needs to be a
> means to easily skip it, or perhaps defer it to run at the next startup.
>  Many people (like me :P) leave it till the very last minute at work
> before doing an "express shutdown" to dash out the door for the train.
> Having the laptop decide that it needs to do a disk scan at that point
> will not be popular...!

I have the same feeling. I often shut down my desktop and file servers
at home over night, and I wouldn't want the file server to stay on for
several hours doing fsck, while I'm trying to get some sleep. (I also
don't like it taking hours to boot up, when fsck-on-boot strikes.)

It seems there is not good to run fsck either during boot or during
shutdown.

As it happens, I made a little experiment to run fsck with -n (supported
by ext2/ext3 mainly) while the system was running, to avoid having to
run it during boot at all. This would be good also for long-running
servers: they could run fsck from cron.

Unfortunately, e2fsck does not handle very well the situation of the
filesystem changing from underneath it, which will happen when running
with -n on a mounted filesystem.

A way to avoid that would be to set up systems with LVM, and use an LVM
snapshot volume for running fsck. This would give fsck a frozen snapshot
of the system, and should work better. However, it requires some free
space to be used, and I haven't actually tried it yet. Reserving some
disk space just for this probably isn't going to be all that popular,
either. However, for systems on which it would be acceptable, it might
be worthwhile to investigate this.