MNT_FORCE does not allow a busy filesystem to be unmounted. Only MNT_DETACH allows that. MNT_FORCE only tries to abort pending transactions, in the hope that might help umount not to block, Also, other filesystems than NFS support MNT_FORCE. Signed-off-by: NeilBrown <neilb@xxxxxxxx> --- Explanation derived from examination of source code. Cc to systemd devel in relation to comment I just posted: https://github.com/systemd/systemd/commit/0c08f5cde749bd2818475e487109cd0d413452df You may want to move the "linux version when support was added" to a comment, or discard it. man2/umount.2 | 14 +++++++++++--- 1 file changed, 11 insertions(+), 3 deletions(-) diff --git a/man2/umount.2 b/man2/umount.2 index 68f76b7c6352..ccd1d07afe88 100644 --- a/man2/umount.2 +++ b/man2/umount.2 @@ -61,9 +61,17 @@ unmounts a target, but allows additional controlling the behavior of the operation: .TP .BR MNT_FORCE " (since Linux 2.1.116)" -Force unmount even if busy. -This can cause data loss. -(Only for NFS mounts.) +Ask the filesystem to abort pending requests before attempting the +unmount. This may allow the unmount to complete without waiting +for an inaccessible server. If, after aborting requests, some +processes still have active references to the filesystem, the +unmount will still fail. In Linux 4.12, only the filesystems +9p (2.6.16), +ceph (2.6.34), +cifs (2.6.12), +fuse (2.6.16), +lustre (3.11), +and NFS (2.1.116) respond to MNT_FORCE. .TP .BR MNT_DETACH " (since Linux 2.4.11)" Perform a lazy unmount: make the mount point unavailable for new -- 2.14.0.rc0.dirty
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