What things are not saved in a btrfs snapshot?

I’m using BTRFS for my root partition and manage its snapshots with Snapper. I decided to create subvolumes for /var/tmp, /var/cache and /var/log as these are constantly changing its data which is not a good idea for scheduled snapshotting. In this way, they are not saved.

However, I noticed that files inside /tmp where included in the snapshots too, which is not what I want. I was mounting a tmpfs filesystem there but it was saved anyways. I ended up creating a subvolume for it.

I noticed that /sys, /run and /proc are not saved (which is a good thing). What do they do to achieve that? can I do the same for /tmp? what things are not saved in a btrfs snapshot? besides other subvolumes, of course.

Asked By: Megver83


Thanks to Kamil Maciorowski’s comment, I realized that I had to clean /tmp before mounting the tmpfs. Now snapshots have an empty /tmp. My mistake was to think that /tmp was cleaned when powering off.

Answered By: Megver83