Ive got a multiple problem with new jail and removal from the first with kqueue
error, device busy for devfs and jail(8) doesn't do ifconfig -alias.

How-To-Repeat: root@netsnap:/usr/jails/var # cat jail1.conf
jail1 {
exec.start = "/bin/sh /etc/rc";
exec.stop = "/bin/sh /etc/rc.shutdown";
exec.clean;
mount.devfs;
host.hostname = "jail1.my.domain";
path = "/usr/jails/jails/jail1";
allow.raw_sockets;
allow.socket_af;
allow.chflags;
allow.sysvipc;
ip4.addr = 192.168.1.67/24;
interface="em0";
devfs_ruleset="4";
}


root@netsnap:/usr/jails/var # ifconfig em0
em0: flags=8843<UP,BROADCAST,RUNNING,SIMPLEX,MULTICAST> metric 0 mtu 9000
       options=98<VLAN_MTU,VLAN_HWTAGGING,VLAN_HWCSUM>
       ether 08:00:27:d3:9a:a9
       inet6 2a01:4f8:61:50c2::13 prefixlen 64 duplicated
       inet6 fe80::a00:27ff:fed3:9aa9%em0 prefixlen 64 scopeid 0x1
       inet 192.168.1.101 netmask 0xffffff00 broadcast 192.168.1.255
       nd6 options=21<PERFORMNUD,AUTO_LINKLOCAL>
       media: Ethernet autoselect (1000baseT <full-duplex>)
       status: active


root@netsnap:/usr/jails/var # jail -f jail1.conf -c jail1
jail1: created
/etc/rc: WARNING: $hostname is not set -- see rc.conf(5).
Creating and/or trimming log files.
ln: /dev/log: Operation not permitted
Starting syslogd.
ELF ldconfig path: /lib /usr/lib /usr/lib/compat
32-bit compatibility ldconfig path: /usr/lib32
Clearing /tmp (X related).
Updating motd:.
Starting cron.

Mon May 14 18:56:27 UTC 2012

Ok, all fine on this moment:

root@netsnap:/usr/jails/var # ifconfig em0
em0: flags=8843<UP,BROADCAST,RUNNING,SIMPLEX,MULTICAST> metric 0 mtu 9000
       options=98<VLAN_MTU,VLAN_HWTAGGING,VLAN_HWCSUM>
       ether 08:00:27:d3:9a:a9
       inet6 2a01:4f8:61:50c2::13 prefixlen 64 duplicated
       inet6 fe80::a00:27ff:fed3:9aa9%em0 prefixlen 64 scopeid 0x1
       inet 192.168.1.101 netmask 0xffffff00 broadcast 192.168.1.255
       inet 192.168.1.67 netmask 0xffffff00 broadcast 192.168.1.255
       nd6 options=21<PERFORMNUD,AUTO_LINKLOCAL>
       media: Ethernet autoselect (1000baseT <full-duplex>)
       status: active


Now dancing with stopping:

root@netsnap:/usr/jails/var # jail -f jail1.conf -r jail1
Stopping cron.
Terminated