 First introduced in FreeBSD version 4, jails is a security mechanism and an implementation of operating-system-level virtualization that enables the user to run multiple instances of a guest operating system on top of a FreeBSD host. It is an enhanced version of the traditional chroot mechanism. A process that runs within such a jail is unable to access the resources outside of it. Every jail has its own hostname and IP address. It is possible to run multiple jails at the same time, but the kernel is shared among all of them. Hence only software supported by the FreeBSD kernel can be run within a jail.
