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.
