Here are a few more notes about how things got setup for my jail I named debian:

Kernel Modules

In /boot/loader.conf, I added these lines:

fdescfs_load="YES"
linprocfs_load="YES"
linsysfs_load="YES"
tmpfs_load="YES"

Mounting Filesystems

Created /etc/fstab.debian and populated with:

linproc     /jails/debian/proc      linprocfs       rw 0 0
linsys      /jails/debian/sys       linsysfs        rw 0 0
tmpfs       /jails/debian/lib/init/rw   tmpfs       rw 0 0

ezjail Config

Created /usr/local/etc/ezjail/debian with these contents:

export jail_debian_hostname="debian"
export jail_debian_ip="127.0.0.6"
export jail_debian_interface="lo0"
export jail_debian_rootdir="/jails/debian"
export jail_debian_mount_enable="YES"
export jail_debian_devfs_enable="YES"
export jail_debian_devfs_ruleset="devfsrules_jail"
export jail_debian_fdescfs_enable="YES"
export jail_debian_exec_start="/etc/init.d/rc 3"
export jail_debian_flags="-l -u root"

I also tried adding an IPv6 address to the jail, and that seems to work OK

So you can now stop/start with jail with

service ezjail.sh stop debian
service ezjail.sh start debian

Connect to the jail console

If you create a symlink for login (so that from the jail's POV there's a /usr/bin/login, like there would be on a FreeBSD jail)

cd /jails/debian/usr/bin/
ln -s ../../bin/login .

then you can use the ezjail-admin command to get a console in the jail, with:

ezjail-admin console debian

Otherwise, I've been using my own script to get a console (which assumes bash is installed in the jail), named /usr/local/sbin/jlogin

#!/bin/sh
#
# log into a jail, running bash
#
JID=`jls | grep " $1 " | awk '{print $1}'`
exec jexec $JID env -i PATH=/sbin:/bin:/usr/sbin:/usr/bin:/usr/local/sbin:/usr/local/bin TERM=$TERM EDITOR=$EDITOR LANG=$LANG HOME=/root bash -l

That runs as:

jlogin debian

I got it running fairly decently, but along the way ran into some small problems - and thought I'd jot down what they were and what the fixes were.

FreeBSD Update

At first, I was using FreeBSD 8.2-RELEASE, and used debootstrap to install Debian Squeeze, as the tutorial showed. Once inside the jail, things sort of worked, but most commands, aptitude especially, would die with:

User defined signal 1

It turns out you need a newer kernel than 8.2 to run kFreeBSD in a chroot, as is mentioned in the FAQ. I upgraded my FreeBSD kernel/world to 8.3-PRERELEASE (2012-02-22), and the "signal 1" problem went away.

Debian Update

The next problem was that aptitude would still die, with:

Uncaught exception: Unable to read from stdin: Operation not permitted

After reading about this bug in cwidget, it seemed an upgrade to Wheezy was needed to fix the problem - and sure enough that problem went away.

kbdcontrol and /dev/console

The upgrade to Wheezy didn't go entirely smoothly, mainly due to the kbdcontrol package (required by sysvinit) being unable to access /dev/console in the jail. I wasn't worried about keeping things in the jail isolated for security reasons, so I went ahead and added /dev/console on-the-fly to the running jail by running outside the jail:

devfs -m /jails/debian/dev rule add path 'console*' unhide
devfs -m /jails/debian/dev rule applyset

After that, the kbdcontrol package was able to be upgraded, and I seem to have a Wheezy FreeBSD jail now. Very cool.

UPDATE: A followup talks more about the actual file changes made to run as an ezjail