Introduction to FreeBSD Jails

FreeBSD jails provide operating system-level virtualisation, allowing you to partition a FreeBSD system into several independent mini-systems called jails.

What Are Jails?

Jails are lightweight containers that share the host kernel but have their own:

File system hierarchy
Network stack (optional)
User accounts
Process space

Why Use Jails?

Security isolation - Compromised services cannot affect the host
Resource management - Limit CPU, memory, and disk usage
Easy deployment - Clone and migrate entire environments
Testing - Safe environment for experiments

Basic Jail Creation

# Create a jail root
mkdir -p /jails/myjail

# Extract base system
tar -xf /path/to/base.txz -C /jails/myjail

# Configure jail in /etc/jail.conf
myjail {
    host.hostname = "myjail.local";
    path = "/jails/myjail";
    exec.start = "/bin/sh /etc/rc";
    exec.stop = "/bin/sh /etc/rc.shutdown";
}

Next Steps

Once you have a basic jail running, explore:

VNET for full network virtualisation
ZFS datasets for jail storage
Jail management tools like iocage or bastille