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umount.2: Move "shared mount + umount" text to a subsection in MOTTES 

Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
This commit is contained in:
Michael Kerrisk 2015-02-02 13:02:02 +01:00
parent 50a4b0aafc
commit 430a1677d2
1 changed files with 33 additions and 33 deletions
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man2/umount.2
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@ -97,39 +97,6 @@ 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.
.PP
Shared mount points cause any mount activity on a mount point, including
.BR umount (2)
operations, to be forwarded to every shared mount point in the
peer group and every slave mount of that peer group.
This means that
.BR umount (2)
of any peer in a set of shared mounts will cause all of its
peers to be unmounted and all of their slaves to be unmounted as well.
This propagation 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
.BR umount (2)
does not propagate in this fashion,
the mount point may be remounted using a
.BR mount (2)
call with a
.I mount_flags
argument that includes both
.BR MS_REC
and
.BR MS_PRIVATE
prior to
.BR umount (2)
being called.
.SH RETURN VALUE
On success, zero is returned.
On error, \-1 is returned, and
@ -197,6 +164,39 @@ are available in glibc since version 2.11.
These functions are Linux-specific and should not be used in
programs intended to be portable.
.SH NOTES
.SS umount() amd shared mount points
Shared mount points cause any mount activity on a mount point, including
.BR umount (2)
operations, to be forwarded to every shared mount point in the
peer group and every slave mount of that peer group.
This means that
.BR umount (2)
of any peer in a set of shared mounts will cause all of its
peers to be unmounted and all of their slaves to be unmounted as well.
This propagation 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
.BR umount (2)
does not propagate in this fashion,
the mount point may be remounted using a
.BR mount (2)
call with a
.I mount_flags
argument that includes both
.BR MS_REC
and
.BR MS_PRIVATE
prior to
.BR umount (2)
being called.
.SS Historical details
The original
.BR umount ()
function was called as \fIumount(device)\fP and would return