mount_namespaces.7: More clearly explain the notion of locked mounts
For a long time, this manual page has had a brief discussion of
"locked" mounts, without clearly saying what this concept is, or
why it exists. Expand the discussion with an explanation of what
locked mounts are, why mounts are locked, and some examples of the
effect of locking.
Thanks to Christian Brauner for a lot of help in understanding
these details.
Reported-by: Christian Brauner <christian.brauner@ubuntu.com>
Acked-by: Christian Brauner <christian.brauner@ubuntu.com>
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>