[buildd-tools-devel] Bug#633671: Bug#633671: schroot behaves differently depending on cwd

[Thibaut VARENE]

On Tue, Jul 12, 2011 at 10:43 PM, Roger Leigh <rleigh at codelibre.net> wrote:
> On Tue, Jul 12, 2011 at 09:50:22PM +0200, Thibaut VARENE wrote:
>> On Tue, Jul 12, 2011 at 9:33 PM, Roger Leigh <rleigh at codelibre.net> wrote:
>>
>> > The reason we don't implement a fallback is because it would make
>> > the behaviour unpredictable.  The exact logic is as follows:
>>
>> OK. I'm not entirely sure I see how it would be unpredictable, and
>> more to the point why dchroot behaves differently from schroot, but
>> then again, I'm not very familiar with either tool.
>
> When you run a command, you might need it to operate in a specific
> directory.  Examples:
>
>  rm foo
>  ls foo
>  make
>  dpkg-buildpackage
>
> If we can't chdir to the specific directory, the results could be
> both unpredictable and disastrous!  In the case of other commands
> such as "apt-get ..." the current directory doesn't matter, but
> there's no way for schroot to know that in advance, so we always
> have to play it safe.

Yeah I get that.

>> The thing is that the error message isn't really explicit, when you're
>> unaware of this "design choice"... I don't how it could be improved
>> though.
>
> We could add an additional information message e.g.
>
> E: Failed to change to directory ‘/tmp/syscheck’: No such file or directory
> I: Does this directory exist inside the chroot?
> I: Use the --directory option to run the command in a different directory.

Well, the problem is that when I first saw the error message, I didn't
realize it was talking about the chroot, but I quickly suspected it
(it wouldn't have made /any/ sense otherwise). This clarifies the
situation. What remains unclear to the average user unaware of the
implications of a fallback policy for commands is /why/ the directory
needs to be in the chroot. Put another way, at some point I started
believing schroot wouldn't work unless the whole /home/buildd was
loop-mounted into the chroot. I didn't realize it only need the
specific directory it was executed from. I suppose some extra
documentation in the manpages regarding the behaviour of schroot when
executing shells vs commands might be helpful to clarify this.

Cheers,
T-Bone

-- 
Thibaut VARENE
http://www.parisc-linux.org/~varenet/