2017-08-08 05:49:58 UTC
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 <***@suse.com>
Explanation derived from examination of source code.
Cc to systemd devel in relation to comment I just posted:
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
@@ -61,9 +61,17 @@ unmounts a target, but allows additional
controlling the behavior of the operation:
.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
+and NFS (2.1.116) respond to MNT_FORCE.
.BR MNT_DETACH " (since Linux 2.4.11)"
Perform a lazy unmount: make the mount point unavailable for new