Cannont umount FUSE filesystems when mounted on a NFS mounted directory in some cases

[Sebastian Urban]

When trying to unmount a FUSE mount that is mounted on a subdirectory of a NFS mounted directory the following error message appears sometimes:

$ sshfs user@host:/home/user/test ./sshfs
$ fusermount -u ./sshfs
umount: user@host:/home/user/test: block devices not permitted on fs
umount: user@host:/home/user/test: block devices not permitted on fs

We have found no way to unmount this directory. fusermount -u -z does not help.

Description: Ubuntu 8.04.2
Release: 8.04

fuse-utils:
  Installed: 2.7.2-1ubuntu2
  Candidate: 2.7.2-1ubuntu2
  Version table:
 *** 2.7.2-1ubuntu2 0
        500 http://de.archive.ubuntu.com hardy/main Packages
        100 /var/lib/dpkg/status

[Joe Pfeiffer (joseph-pfeifferfamily)]

I came across this today in another distribution. It turned out to be a protections issue; one of the ancestor directories wasn't accessible by root.

umount gives the error message you cite when it receives an EACCES error return, which is extremely misleading. I wonder if this should be reported as a bug against util-linux?

[Luboš Doležel (lubos-dolezel)]

I confirm the problem. When root cannot access the home directory of the user (which is a common case with NFS mounts), it is impossible to unmount a FUSE mount.