Application Jail Shutdown Problem

[Michael W. Lucas]

On Wed, May 01, 2019 at 08:53:18AM -0600, James Gritton wrote:
> On 2019-04-30 12:03, squiggly foo wrote:
> > Hi All,
> > 
> > I use the mount.fstab parameter to mount a number of file systems
> > before starting a jail which works without any problem.  However since
> > it is an application jail, there are no other processes running inside
> > the jail other than the one application.  As soon as that application
> > terminates the jail is removed by the host.
> > 
> > This is actually my preferred behavior; I want the jail to be removed
> > when the process inside of it terminates.  But the problem is that the
> > mount points are not unmounted after the jail is removed that way.
> > The only way I can get the jails to unmount is if I do a "jail -r
> > jailname" which is what I want to avoid as I would not do that while
> > the process inside the jail is still running.
> > 
> > 
> > Does anyone know of a way for the jails to umount the mount points in
> > its fstab file when the only process inside the jail exits?
> 
> No easy way.  Those filesystems have to be unmounted by somebody; the
> jail can't do it because it doesn't have the permission (because it 
> didn't
> mount them).  So some process needs to be watching to see when the jail
> goes away.  That would be some kind of watcher that wakes up 
> occasionally
> and sees if the jail is still there.  It might be nice to have some 
> kqueue
> support for jails.


Maybe I'm not understanding the problem.

Is there a reason why exec.poststop="umount -aF /whatever/jail.fstab"
won't do the trick?

==ml

-- 
Michael W. Lucas 	https://mwl.io/
author of: Absolute OpenBSD, SSH Mastery, git commit murder,
Immortal Clay, PGP & GPG, Absolute FreeBSD, etc, etc, etc...