How to detect a file system's dirty bit?
 

Is it possible to detect a file system's dirty bit before attempting to mount it?

The question arises for a backup script. Ideally it would run fsck if required before mounting to minimise the logging verbosity associated with a failed mount.

In case the answer depends on the file system type, ext4 and JFS are of particular interest; others would be nice.

With ext.*fs you could

Thanks unSpawn :)

And similarly with JFS2, jfs_tune -l and parse the "JFS state:" value from the output. Unlike for ext*, the state shows as "mounted" when it is, er, mounted; that can be convenient.

Finally we do not check JFS file systems to see if they are dirty before mounting them. It is so "cheap" to fsck a JFS file system that the cost of coding to avoid doing so unnecessarily is not justified. That can be a deciding factor between ext4 and JFS.