why /dev/ptmx is in the snapshots?

why /dev/ptmx is in the snapshots?

[Marc Pignat]

I have a btrfs root partition and I use snapper to automatically take snapshots (ubuntu 18.04 LTS). 

The `/dev/ptmx` file change between each snapshots despite `/dev` is mounted as a devtmpfs file system.

I have tried creating a file in `/dev`, and as expected it is not snapshotted.

My first intuition was that one service was started before `/dev` is mounted as a devtmpfs and still using it, but `sudo fuser /dev/ptmx` show no use of that file.


Can someone explain this behavior?

Thank you in advance and best regards






Marc


P.S: This is a repost of one of my questions on askubuntu.com, since I still don't have any answer.

Re: why /dev/ptmx is in the snapshots?

[Marc Pignat]

On 11/12/18 1:50 PM, Remi Gauvin wrote:
> On 2018-11-12 07:26 AM, Marc Pignat wrote:
...
> fuser /mnt/sda3/@/dev/ptmx

Done the mount somewhere else thing, still no user of this file...

> 
> Depending on how Ubuntu was installed, you might not have the @
> subvolume.  I think then, root is just written straight to the root of
> the fs, so fuser /mnt/sda3/dev/ptmx
> 

Sure, Ubuntu installer creates a @ and @home volumes.

I think I've found the problem source (not the solution).

Every time I run snapper create the next status will show:
....xa /dev/ptmx and
c..... /var/log/snapper.log

And if fact, the log files says something about the /dev/ptmx file:

2018-11-12 14:07:53 ERR libsnapper(11939) XAttributes.cc(XAttributes):154 - Couldn't get xattributes names-list size. link: //.snapshots/8/snapshot/dev/ptmx, error: No such file or directory

After the snapshot, the file /mnt/test/@/.snapshots/8/snapshot/dev/ptmx is existing.

Is this a problem in snapper?