error creating thin jail on 15.0

[Graham Menhennitt]

Hello,

I've recently upgraded my server from 14.3 to 15.0. Everything appeared
to work successfully in the upgrade.

I now want to create a thin jail using UFS. I've followed the handbook
section 17.5 exactly except that my jail is named "vaultwarden" instead
of "thinjail". Accordingly, I've replaced "thinjail" by "vaultwarden"
everywhere.

When I try to start the jail, I get an error:

# service jail start vaultwarden
Starting jails: cannot start jail  "vaultwarden":
jail: vaultwarden: mount.devfs:
/usr/local/jails/containers/vaultwarden/dev: No such file or directory
.
#

I tried creating directory /usr/local/jails/containers/vaultwarden/dev.
Then I get a different error:

# service jail start vaultwarden
Starting jails: cannot start jail  "vaultwarden":
1
jail: vaultwarden: /bin/sh /etc/rc: failed
.
#

I'm completely new to jails. Can somebody please give me a clue on how
to diagnose then problem.

Thanks in advance,

    Graham