jail not found error?

[Grzegorz Junka]

I am trying to set up a Centos 6 jail. It fails with the following error:

root at ultrabook:~ # service jail start centos6
Starting jails: centos6jls: jail "centos6" not found
.

I somehow managed to run it once by changing the start script from:

exec.start = "/bin/sh /etc/rc";

to

exec.start = "/etc/rc 3";

It started once but after I shut it down it shows the same error again 
wherever I am trying to start it. This is what I have configured so far:

root at ultrabook:~ # cat /etc/jail.conf
# Use the rc scripts to start and stop jails. Mount jail's /dev.

#exec.start = "/bin/sh /etc/rc";
#exec.stop = "/bin/sh /etc/rc.shutdown";
exec.clean;

allow.mount;
mount.devfs;
mount.fstab = "/usr/local/etc/fstab/$name";
devfs_ruleset = 4;

path = "/j/$name";
host.hostname = "$name.ultrabook.yoonka.com";
exec.consolelog = "/var/log/jail/$name";

centos6 {
   exec.start = "/etc/rc 3";
   ip4.addr = 127.0.2.1;
   interface = lo0;
}


root at ultrabook:~ # cat /usr/local/etc/fstab/centos6
linsys    /j/centos6/sys         linsysfs  rw 0 0
linproc   /j/centos6/proc        linprocfs rw 0 0
#tmpfs     /j/centos6/lib/init/rw tmpfs     rw,mode=777 0 0
/devfs    /j/centos6/dev         devfs     rw,ruleset=4 0 0

I was following this example:

https://bluehatrecord.wordpress.com/2015/09/19/the-midnight-oil-jailing-centos6-in-freebsd-10-2/

but wanted to use the new configuration files. My system:

root at ultrabook:~ # uname -a
FreeBSD ultrabook.yoonka.com 10.3-RELEASE FreeBSD 10.3-RELEASE #0 r297264: Fri Mar 25 02:10:02 UTC 2016     root at releng1.nyi.freebsd.org:/usr/obj/usr/src/sys/GENERIC  amd64

How to fix or debug this 'jail "centos6" not found' error and start the 
jail?

Grzegorz