Freebsd jail setup: thin jail

Thin jails are jails that mount a basejail as readonly.
This basejail is generally shared with several other jails.

NOTE:

Thin jails have been criticized for being difficult to manage, particularly for updates.
If you have the disk space, create a thick jail instead.

FreeBSD <=10

Create jail in filesystem

# Create New Jails (within system)
mkdir -p /home/j/gitbox/s
mkdir -p /home/js/gitbox

mkdir /home/js
cpdup /home/j/skel /home/js/gitbox

/home/j/{jail}/etc/resolv.conf

# /home/j/gitbox/etc/resolv.conf
nameserver 192.168.1.1  # router ip addr

/etc/jails/{jail}.fstab

Each jail can now store it's own fstab, keeping your root system's fstab clean.

You can keep this file wherever you'd like.
Reference it within your jail.conf's mount.fstab setting.

# /etc/jails/{yourjail}.fstab
/home/j/jbase    /home/j/gitbox    nullfs   ro  0   0
/home/js/gitbox  /home/j/gitbox/s  nullfs   rw  0   0

/etc/jail.conf

Jail options can be set for all jails by writing them outside of a jail's scope.
Jail options can be referenced within other options using bash variable syntax.
All options can be defined either globally, or for a specific jail.

# /etc/jail.conf

exec.start="/bin/sh /etc/rc";
exec.stop="/bin/sh /etc/rc.shutdown";
mount.fstab = "/etc/jails/${host.hostname}.fstab";
path=/home/jail/${host.hostname};

wikijail {
   allow.mount;
   allow.mount.devfs;
   allow.mount.nullfs;
   host.hostname=wikijail;
   ip4.addr=192.168.1.131;
}

FreeBSD <10

Create jail in filesystem

# Create New Jails (within system)
mkdir -p /home/j/gitbox/s
mkdir -p /home/js/gitbox

mkdir /home/js
cpdup /home/j/skel /home/js/gitbox

/home/j/{jail}/etc/resolv.conf

# /home/j/gitbox/etc/resolv.conf
nameserver 192.168.1.1  # router ip addr

/etc/fstab

In FreeBSD 9, jail mounts had to be declared within your host-server's fstab.

# /etc/fstab
/home/j/jbase    /home/j/gitbox    nullfs   ro  0   0
/home/js/gitbox  /home/j/gitbox/s  nullfs   rw  0   0