Stupid Linux Tricks: force a filesystem journal replay without mounting (filesystem-agnostic!)

This might actually be a bug in the mount command, but, for any filesystem:

mount /dev/sdXy nonexistent_mountpoint 

Will invoke the filesystem driver to fully prepare the filesystem for mounting, and only fails at the very end when it realises the mountpoint path doesn't exist. This includes journal replay, device scan/addition, etc.

So, if you ever have a weird use case where you need to do this to filesystems but want to save yourself the extra "unmount" command, there you go. Yes, most filesystems' check tools have a way to do the same thing, but that varies, and this way you don't have to remember anything filesystem-specific.

(My weird edge case where this is handy: I need to fsck filesystems that are temporarily attached from VMs that had something bad happen to their underlying storage, and the fsck equivalent for some of them, e.g. xfs_repair -n , cares about the journal being cleared by a normal mount first. Don't worry; it doesn't matter that the journal replay is a write operation; I'm working on throwaway clones of these VMs.)