Signed-off-by: Eric W. Biederman <ebiederm@xxxxxxxxxxxx> --- man2/umount.2 | 18 ++++++++++++++++++ 1 file changed, 18 insertions(+) diff --git a/man2/umount.2 b/man2/umount.2 index aea39d8306fe..a0120b2fc811 100644 --- a/man2/umount.2 +++ b/man2/umount.2 @@ -97,6 +97,24 @@ Don't dereference if it is a symbolic link. This flag allows security problems to be avoided in set-user-ID-\fIroot\fP programs that allow unprivileged users to unmount filesystems. + +.P +Shared mount points cause any mount activity on that mount point +including umounts to be forwarded to every shared mount point in it's +peer group and every slave mount of that peer group. This means that +umount of any peer in a set of shared mounts will cause all of it's +peers to be unmounted and all of their slaves to be unmounted as well. + +This propogagtion of unmount activity can be particularly surprising +on systems where every mount point is shared by default. On such +systems recursively bind mounting the root directory of the filesystem +onto a subdirectory and then later unmounting that subdirectory with +.BR MNT_DETACH +will cause every mount in the mount namespace to be lazily unmounted. + +To ensure umount does not propagate the mount point may be +remounted with MS_REC | MS_PRIVATE prior to umount being called. + .SH RETURN VALUE On success, zero is returned. On error, \-1 is returned, and -- 1.9.1 -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
