Based on patch from Mike Frysinger <vapier@gentoo.org>.
Mike Frysinger wrote:
When it comes to pid namespaces, it's also useful for /proc to reflect
the current namespace. Again, this is easy to pull off, but annoying
to force everyone to do it themselves. So let's add a --mount-proc to
do the magic for us. The downside is that this also implies creating
a mount namespace as mounting the new pid namespace /proc over top the
system one will quickly break all other processes on the system.
Signed-off-by: Karel Zak <kzak@redhat.com> Acked-by: Mike Frysinger <vapier@gentoo.or>