Hi

When using cowbuilder --login with a bindmount, I occasionally hit a
problem where umounting fails on exiting from the chroot.

Here, pbuilder/cowbuilder as a precaution aborts the exit and forces you
to solve the problem to avoid trashing your files. This is great.

In my case, I cannot always figure out why the mount point refuses to
unmount but a lazy unmount (umount -l) gets the job done enough that my
files are no longer in danger.  Doing that causes pbuilder to still fail
on exit now with:

umount: /var/cache/pbuilder/build/cow.XXX/path/to/mp: not mounted.

And then throws me back into the chroot. So, to "unstuck" this, I end up
having first to umount the mountpoint manually and then manually remount
something else at that mountpoint, so pbuilder/cowbuilder get continue.

I think it would be nice if pbuilder could test if the mountpoint is
still a mountpoint.  Since `mountpoint` is in `util-linux` (Essential:
yes), this could be done with:


   IS_MOUNTED=true
   mountpoint -q "$MP" || RC=$?
   if [ "${RC}" = "32" ]; then
       IS_MOUNTED=false
   fi


For safety, I would recommend always doing umount, if that fails but
mountpoint says the path is not a mountpoint, then it can progress.

Best regards,
Niels

Niels Thykier dixit:

There’s also the option of getting a fresh view of the sub-mounts
from /proc/mounts; see e.g. the debchroot_umtree code in
https://evolvis.org/plugins/scmgit/cgi-bin/gitweb.cgi?p=shellsnippets/shellsnippets.git;a=blob;f=posix/sysadmin/debchroot.sh;hb=HEAD
which umounts everything under a given directory (in reverse order)
and is even POSIX sh. I’m in the position to dual-licence that if
needed.

bye,
//mirabilos

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