userland shutdown(2)?

[Harry Schmalzbauer]

 Hello,

stoping jails leaves open sockets with no process attached.
(sockstat shows like this line:
?        ?          ?     ?  tcp6   2001:db8::fedc:389 2001:db8::abcd:15666
)

Since I make use of mount lines in jail.conf,
umounting the root filesystem of the jail fails because "device busy".
To avoid dirty filesystems after reboot of the host,
my modified rc.d/jail updates the corresponding filesystem
to be mounted readonly, but that's not a great solution.

I'd like to get all sockets killed before jail vanishes.

There's shutdown(2), which seems to do exactly what I want,
but where/how to implement?
Is there any userland tool utilizing shutdown(2)?

Thanks,

-Harry