Linux supports a mount 'subtype', which, according to man mount(8) is "defined by a '.subtype' suffix." Widely used fuse fileysystems like sshfs identify themselves with a subtype. I.e., they show up in the mnt_type field as 'fuse.sshfs'. Other filesysems may use subtype as well.

When an administrator or packager puts 'fuse' (or another fstype that supports or encourages subtyping) in PRUNEFS, their intention is clearly to prune all filesystems of type 'fuse', regardless of subtype.

The attached patch changes updatedb's behavior so that PRUNEFS only matches the filesystem type and ignores any '.subtype'. It also reports both the original mnt_type and the modified type when --debug-pruning is enabled.