Debian Bug report logs - #648459
schroot doesn't mount /home submount into the chroot

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Message #5 received at submit@bugs.debian.org (full text, mbox, reply):

From: Wookey <wookey@wookware.org>

To: bugs@debian.org

Subject: schroot doesn't mount /home submount into the chroot

Date: Fri, 11 Nov 2011 18:17:18 +0000

[Message part 1 (text/plain, inline)]

Package:schroot
Version:1.4.19
Subject:schroot doesn't mount /home submounts into the chroot

If you use schroot on a machine used in a large company or institution
it is likely that your $home mount is actually mounted on /home/user,
not /home. 

Because the default fstab mounts /home with bind, rather then rbind
this means that you don't see the real $HOME inside the chroot. I have
such a machine at work, which is how I noticed this issue.

What I actually see inside the chroot is the underlying almost-empty
/home/wookey that is obscured by the real /home/wookey when it is
mounted. (This is of course exptremely confusing for while until you
work out what the hell is going on).

Is there a good reason not to make rbind the default for /home in the
same way that it now is for /proc and /sys? Then users would get the
full 'schroot experience' where their $HOME is just the same insde the
chroot as outside.

I've attached a patch for this changing the default config. Perhaps it
should apply to the desktop config too - I'm not sure exactly how
those are used? 

This bug was originally found and reported on Ubuntu (
https://bugs.launchpad.net/ubuntu/+source/schroot/+bug/791908 ). 

Wookey
-- 
Principal hats:  Linaro, Emdebian, Wookware, Balloonboard, ARM
http://wookware.org/

[schroot-home-rbind.patch (text/x-diff, attachment)]

Message #10 received at 648459@bugs.debian.org (full text, mbox, reply):

From: Roger Leigh <rleigh@codelibre.net>

To: Wookey <wookey@wookware.org>, 648459@bugs.debian.org

Subject: Re: [buildd-tools-devel] Bug#648459: schroot doesn't mount /home submount into the chroot

Date: Sat, 12 Nov 2011 00:27:30 +0000

On Fri, Nov 11, 2011 at 06:17:18PM +0000, Wookey wrote:
> Package:schroot
> Version:1.4.19
> Subject:schroot doesn't mount /home submounts into the chroot
> 
> Is there a good reason not to make rbind the default for /home in the
> same way that it now is for /proc and /sys? Then users would get the
> full 'schroot experience' where their $HOME is just the same insde the
> chroot as outside.

We found recently that autofs does not play nicely with rbind, which
led to complete removal of rbind from the profile fstabs in
etc/profile-templates in the source.  We now explicitly list each
bind mount.

I wasn't happy with doing this, especially since it's most likely
a kernel bug.  You actually end up with unmountable mounts, and need
to reboot the entire system after running schroot since it's not
possible to umount.  We noticed this was occuring with rbind of /dev
when using systemd, since systemd creates a number of autofs mounts
under /dev.  However, the problem affects all autofs mounts, not only
those created by systemd.  We can't be sure that the host isn't using
autofs, hence we chose to go with the safe approach of not using
rbind, and avoid the need to reboot the system to recover in such
cases.

Were the bug with binding of autofs mounts to be fixed, we would then
certainly reconsider using rbind again.  I'm not sufficiently familiar
with the kernel to look at fixing it myself.


Regards,
Roger

-- 
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