Jail problems

I'm trying to setup several jails for the first time, but I'm having 
difficulties.

After following instructions in man jail, when i start a shell in a jail, I 
cannot start top or ps in it; the error messages are:

# top
kvm_open: bad namelist
# ps
ps: bad namelist

(on another jail they complain: kvm_open: /dev/null: No such file or 
directory; ... /kernel in the jail is linked to /dev/null as is stated in 
the manual; also, procfs is mounted ok.)

Also, I have sshd_enable="YES" in the jail's /etc/rc.conf, and I see the 
sshd startup message when "booting" jail with /etc/rc, but the process isn't 
there. Starting 'sshd' on the command line seems to work, but upon loggin in 
to the jail a following warning is displayed:

Warning: no access to tty (Bad file descriptor). Thus no job control in this 
shell.

... and the session seems to 'hang', after displaying some garbled lines of 
motd (I think).

vipw cannot be started:
vipw: pw_edit(): No such file or directory

(/etc/master.passwd and /etc/spwd.db exist in the jail)


This is probably something big and obvious I'm missing, but what?

-- 
Every sufficiently advanced magic is indistinguishable from technology
    - Arthur C Anticlarke