How to terminate a lot of jails correctly

[S.N.Grigoriev]

Hi list,

I use a server (FreeBSD 8.1R amd64) with two dozens of jails configured.
I've found out that only a few of them are terminated normally (via
/etc/rc.shutdown) during the system shutdown. FreeBSD reports that
20sec interval has elapsed and simply kills all the jails that are not yet
terminated. I would like to know in what way can I fix it using the system
tools only (not ezjail, Qjail etc).
 
Thanks,
Serguey.