What do "snapper mount" and "snapper umount" do? I'm using snapper with BTRFS under Ubuntu 16.04, and I'm confused about the "mount" and "umount" parameters. They are documented like this in the man page: mount number Mount a snapshot. Not required for all filesystem types. umount number Unmount a snapshot. Not required for all filesystem types. But where are the snapshots mounted? Does snapper read my mind to know, or just makes an educated guess? I know how to mount the snapshots using "mount" and the subvol ID, but I would like to know if these "mount" and "umount" options are just a joke or something you can actually use. Thanks in advance.

`snapper mount` and `snapper umount` are really only useful when snapper is used with thin-provisioned LVM snapshots. Theese commands will mount and unmount LVM snapshots in the `.snapshots/$number/snapshot` directory.

Since btrfs subvolumes are always accessible form the `.snapshots` directory without having to be mounted, `snapper mount` and `snapper umount` don't do anything with btrfs.