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# 16.5 Fine Tuning and Administration

There are several options which can be set for any jail, and various ways of combining a host FreeBSD system with jails, to produce higher level applications. This section presents:

- Some of the options available for tuning the behavior and security restrictions implemented by a jail installation.

- Some of the high-level applications for jail management, which are available through the FreeBSD Ports Collection, and can be used to implement overall jail-based solutions.

## 16.5.1 System Tools for Jail Tuning in FreeBSD

Fine tuning of a jail's configuration is mostly done by setting sysctl(8) variables. A special subtree of sysctl exists as a basis for organizing all the relevant options: the `security.jail.*` hierarchy of FreeBSD kernel options. Here is a list of the main jail-related sysctls, complete with their default value. Names should be self-explanatory, but for more information about them, please refer to the jail(8) and sysctl(8) manual pages.

- `security.jail.set_hostname_allowed: 1`

- `security.jail.socket_unixiproute_only: 1`

- `security.jail.sysvipc_allowed: 0`

- `security.jail.enforce_statfs: 2`

- `security.jail.allow_raw_sockets: 0`

- `security.jail.chflags_allowed: 0`

- `security.jail.jailed: 0`

These variables can be used by the system administrator of the host system to add or remove some of the limitations imposed by default on the `root` user. Note that there are some limitations which cannot be removed. The `root` user is not allowed to mount or unmount file systems from within a jail(8). The `root` inside a jail may not load or unload devfs(8) rulesets, set firewall rules, or do many other administrative tasks which require modifications of in-kernel data, such as setting the `securelevel` of the kernel.

The base system of FreeBSD contains a basic set of tools for viewing information about the active jails, and attaching to a jail to run administrative commands. The jls(8) and jexec(8) commands are part of the base FreeBSD system, and can be used to perform the following simple tasks:

- Print a list of active jails and their corresponding jail identifier (JID), IP address, hostname and path.

- Attach to a running jail, from its host system, and run a command inside the jail or perform administrative tasks inside the jail itself. This is especially useful when the `root` user wants to cleanly shut down a jail. The jexec(8) utility can also be used to start a shell in a jail to do administration in it; for example:

      # jexec 1 tcsh

## 16.5.2 High-Level Administrative Tools in the FreeBSD Ports Collection

Among the many third-party utilities for jail administration, one of the most complete and useful is `sysutils/jailutils`. It is a set of small applications that contribute to jail(8) management. Please refer to its web page for more information.

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