/proc/self/mounts in chroot vs lxc

/proc/self/mounts in chroot vs lxc

[Harald Dunkel]

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Hi folks,

AFAIK /proc/mounts (-> self/mounts) is supposed to replace
/etc/mtab. Problem is: In a chroot it contains too much
(invalid) information about the parent's mount points. It is
very hard to figure out which lines are correct.

For lxc there seems to be no such problem, so I wonder if it
would be possible to extend this scheme to chroot?

I am not sure if this is a kernel or libc issue. Any helpful
comment would be highly appreciated.


Regards

Harri
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Re: /proc/self/mounts in chroot vs lxc

[Michael Tokarev]

On 05.02.2012 12:43, Harald Dunkel wrote:
> Hi folks,
> 
> AFAIK /proc/mounts (-> self/mounts) is supposed to replace
> /etc/mtab. Problem is: In a chroot it contains too much
> (invalid) information about the parent's mount points. It is
> very hard to figure out which lines are correct.
> 
> For lxc there seems to be no such problem, so I wonder if it
> would be possible to extend this scheme to chroot?
> 
> I am not sure if this is a kernel or libc issue. Any helpful
> comment would be highly appreciated.

/proc is _always_ kernel thing.

For lxc, it creates a separate namespace where all "extra" mounts
are unmounted.  So /proc/mounts does not contain unnecessary
entries.

But plain chroot does not create new namespace, the process inherits
parent namespace, so there is no way to clean in up cleanly.

This is how it always worked, I'd say it is too late to change
this, and changing it isn't really trivial due to various
implications bind mounts are giving us.

I think anway.

/mjt.

Re: /proc/self/mounts in chroot vs lxc

[Harald Dunkel]

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On 02/05/12 11:33, Michael Tokarev wrote:
> 
> But plain chroot does not create new namespace, the process inherits parent namespace, so there is no way to clean in up cleanly.
> 

If I do a chroot to /mnt, then there is no "/mnt" in /proc/self/mounts
within this environment. Instead I see yet another entry for '/'.
This certainly looks like something private.

Maybe it would be easier for everybody if /proc/mounts (without "/self")
could always show the "real" mount points at the top level? A bind mount
of /abc to /mnt/abc would appear as /mnt/abc in /proc/mounts at all levels.
I could live with that.



Regards

Harri
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