[Pkg-sysvinit-devel] Bug#494001: Bug: mount: "user" mounts broken when /etc/mtab is a symlink

[Chuck Lever]

On Jan 9, 2011, at 7:37 AM, Roger Leigh wrote:

> On Tue, Jun 23, 2009 at 09:31:12PM +0200, Karel Zak wrote:
>> On Tue, Jun 23, 2009 at 11:32:44AM +0100, Roger Leigh wrote:
>>> On Mon, Jun 22, 2009 at 09:17:18PM +0200, Karel Zak wrote:
>>>> 
>>>> My plan is to support systems without /etc/mtab and use
>>>> /proc/self/mountinfo in util-linux-ng 2.{17,18} (September/October
>>>> 2009 or so...).
>>> 
>>> Cool.  Just to clarify: at this point, barring any unforseen bugs,
>>> we can delete /etc/mtab and running with just /proc will be a
>>> valid supported configuration?
>> 
>> Yes, mtab is Bad Thing.
>> 
>>> What will the minimum supported kernel version for such a configuration
>>> be (with mountinfo)?
>> 
>> kernel 2.6.26
> 
> Hi Karel,
> 
> I know this mail was from quite some time ago, but I've not been able
> to push this change in Debian for a while due to our freeze.  As soon
> as we're released, hopefully in a month or so, removing mtab will be
> on my TODO list again.
> 
> I just wanted to check with you which versions of util-linux-ng would
> work correctly with /etc/mtab removed, since they hadn't been released
> when we last wrote.  I didn't see anything in the 2.17/2.18 release
> notes, but did in 2.19, albeit with the libmount support, marked
> experimental.
> 
> If 2.19 is required, I'd be interested to know how experimental libmount
> support is.  i.e. are there any known regressions or failing use cases
> which we should be aware of, or any other reasons not to enable it at
> this point?

Are you aware of the NFS umount command's dependencies on the information in /etc/mtab?

When performing a umount, the mount.nfs command uses /etc/mtab to save the options that were used to mount that mount point (ie, options that enable the client to contact the server, and which NFS version the mount point uses).  Making /etc/mtab a link to /proc/mounts makes that whole process less reliable, so expect to see reports of umount failures with NFSv2 and NFSv3 in some corner cases.

We are hoping to use libmount, eventually, to store the command-line mount options somewhere besides /etc/mtab so that umount.nfs can continue to work reliably without /etc/mtab.

> Upgrades should be smooth given that we have 2.6.26 in stable as well.
> Have you removed mtab in Fedora/RedHat yet?
> 
> 
> Many thanks,
> Roger
> 
> 
> (I'm not subscribed to the util-linux-ng list, so a CC on any reply
> would be appreciated, thanks!)
> 
> -- 
>  .''`.  Roger Leigh
> : :' :  Debian GNU/Linux             http://people.debian.org/~rleigh/
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-- 
Chuck Lever
chuck[dot]lever[at]oracle[dot]com