Re: [gentoo-user] How to unmount bind-mounted /dev?

[Mick]

On Sunday 01 May 2011 14:08:36 Alex Schuster wrote:
> Mick writes:
> > On Sunday 01 May 2011 00:48:38 Alex Schuster wrote:
> > > The lazy unmount was Thomas' hint already and worked, the partition is
> > > no longer mounted. But I cannot fsck it, it is still in use. cryptsetup
> > > luksClose works neither.
> > > It's no big trouble, but still I'm curious why this is.
> >
> > Asking the obvious:  could this message be there because this partition
> > is still mounted?
>
> I grepped /proc/mounts for it and saw no references. I'm pretty sure I did
> not overlook something. And it's already the second time I tried this, one
> month ago the same had happened, but I did not care about it then.
>
> > Did you check that this partition has been unmounted
> > from all mount points, both original mount point and bind-mount?
>
> The partition only has one mount point, but others were mounted inside it:
>
> /dev/mapper/32 on /32             type ext3 (rw,noatime)
> /dev           on /32/dev         type none (rw,bind)
> /proc          on /32/proc        type none (rw,bind)
> /home          on /32/home        type none (rw,bind,noatime)
> /var/portage   on /32/var/portage type none (rw,bind,noatime)
>
> /var/portage has another file system inside for the portage tree. When I
> want to unmount /32/var/portage, I have to unmount /32/var/portage/tree
> first. All except /32/dev could be unmounted, for /32/dev I needed the -l
> option to mount. Then /32 itself could be unmounted. But things like fsck
> or 'cryptsetup remove' failed, /dev/mapper/32 was in use.
>
> Then I rebooted, but I had forgotten to save my changes to fstab, so all
> those things were again mounted. I tried again anyway, and this time there
> was no problem. I had to use umount -l for /32/dev again, and this time
> also for /32/proc (that was not necessary the last time), but after
> unmounting /32, I could fsck its partition and shrink it.
>
> I have no idea why it did not work the last times I tried. I'll try to
> reproduce this from time to time, maybe after some more uptime and work on
> this partition it will happen again.

Yes, you've done the right thing, unmounting directories from the lower to the 
higher, before you try to unmount the top of the tree.  I would think that 
/dev and /proc would be accessed by the OS in real time, every time you 
read/write to a device/memory/acpi, etc. so trying to umount them could be 
more troublesome.  Perhaps immediately after rebooting there was not much 
activity from previous actions and that's why you were able to unmount them 
without too much trouble.

-- 
Regards,
Mick