15.6. Managing Jails with ezjail

Originally contributed by Warren Block.

Creating and managing multiple jails can quickly become tedious and error-prone. Dirk Engling's ezjail automates and greatly simplifies many jail tasks. A basejail is created as a template. Additional jails use mount_nullfs(8) to share many of the basejail directories without using additional disk space. Each additional jail takes only a few megabytes of disk space before applications are installed. Upgrading the copy of the userland in the basejail automatically upgrades all of the other jails.

Additional benefits and features are described in detail on the ezjail web site, https://erdgeist.org/arts/software/ezjail/.

15.6.1. Installing ezjail

Installing ezjail consists of adding a loopback interface for use in jails, installing the port or package, and enabling the service.

  1. To keep jail loopback traffic off the host's loopback network interface lo0, a second loopback interface is created by adding an entry to /etc/rc.conf:


    The second loopback interface lo1 will be created when the system starts. It can also be created manually without a restart:

    # service netif cloneup
    Created clone interfaces: lo1.

    Jails can be allowed to use aliases of this secondary loopback interface without interfering with the host.

    Inside a jail, access to the loopback address is redirected to the first IP address assigned to the jail. To make the jail loopback correspond with the new lo1 interface, that interface must be specified first in the list of interfaces and IP addresses given when creating a new jail.

    Give each jail a unique loopback address in the netblock.

  2. Install sysutils/ezjail:

    # cd /usr/ports/sysutils/ezjail
    # make install clean
  3. Enable ezjail by adding this line to /etc/rc.conf:

  4. The service will automatically start on system boot. It can be started immediately for the current session:

    # service ezjail start

15.6.2. Initial Setup

With ezjail installed, the basejail directory structure can be created and populated. This step is only needed once on the jail host computer.

In both of these examples, -p causes the ports tree to be retrieved with portsnap(8) into the basejail. That single copy of the ports directory will be shared by all the jails. Using a separate copy of the ports directory for jails isolates them from the host. The ezjail FAQ explains in more detail: http://erdgeist.org/arts/software/ezjail/#FAQ.

    • To Populate the Jail with FreeBSD-RELEASE

      For a basejail based on the FreeBSD RELEASE matching that of the host computer, use install. For example, on a host computer running FreeBSD 10-STABLE, the latest RELEASE version of FreeBSD -10 will be installed in the jail):

      # ezjail-admin install -p
    • To Populate the Jail with installworld

      The basejail can be installed from binaries created by buildworld on the host with ezjail-admin update.

      In this example, FreeBSD 10-STABLE has been built from source. The jail directories are created. Then installworld is executed, installing the host's /usr/obj into the basejail.

      # ezjail-admin update -i -p

      The host's /usr/src is used by default. A different source directory on the host can be specified with -s and a path, or set with ezjail_sourcetree in /usr/local/etc/ezjail.conf.


The basejail's ports tree is shared by other jails. However, downloaded distfiles are stored in the jail that downloaded them. By default, these files are stored in /var/ports/distfiles within each jail. /var/ports inside each jail is also used as a work directory when building ports.


The FTP protocol is used by default to download packages for the installation of the basejail. Firewall or proxy configurations can prevent or interfere with FTP transfers. The HTTP protocol works differently and avoids these problems. It can be chosen by specifying a full URL for a particular download mirror in /usr/local/etc/ezjail.conf:


See Section A.2, “FTP Sites” for a list of sites.

15.6.3. Creating and Starting a New Jail

New jails are created with ezjail-admin create. In these examples, the lo1 loopback interface is used as described above.

Procedure 15.1. Create and Start a New Jail
  1. Create the jail, specifying a name and the loopback and network interfaces to use, along with their IP addresses. In this example, the jail is named dnsjail.

    # ezjail-admin create dnsjail 'lo1|,em0|'


    Most network services run in jails without problems. A few network services, most notably ping(8), use raw network sockets. In jails, raw network sockets are disabled by default for security. Services that require them will not work.

    Occasionally, a jail genuinely needs raw sockets. For example, network monitoring applications often use ping(8) to check the availability of other computers. When raw network sockets are actually needed in a jail, they can be enabled by editing the ezjail configuration file for the individual jail, /usr/local/etc/ezjail/jailname. Modify the parameters entry:

    export jail_jailname_parameters="allow.raw_sockets=1"

    Do not enable raw network sockets unless services in the jail actually require them.

  2. Start the jail:

    # ezjail-admin start dnsjail
  3. Use a console on the jail:

    # ezjail-admin console dnsjail

The jail is operating and additional configuration can be completed. Typical settings added at this point include:

  1. Set the root Password

    Connect to the jail and set the root user's password:

    # ezjail-admin console dnsjail
    # passwd
    Changing local password for root
    New Password:
    Retype New Password:
  2. Time Zone Configuration

    The jail's time zone can be set with tzsetup(8). To avoid spurious error messages, the adjkerntz(8) entry in /etc/crontab can be commented or removed. This job attempts to update the computer's hardware clock with time zone changes, but jails are not allowed to access that hardware.

  3. DNS Servers

    Enter domain name server lines in /etc/resolv.conf so DNS works in the jail.

  4. Edit /etc/hosts

    Change the address and add the jail name to the localhost entries in /etc/hosts.

  5. Configure /etc/rc.conf

    Enter configuration settings in /etc/rc.conf. This is much like configuring a full computer. The host name and IP address are not set here. Those values are already provided by the jail configuration.

With the jail configured, the applications for which the jail was created can be installed.


Some ports must be built with special options to be used in a jail. For example, both of the network monitoring plugin packages net-mgmt/nagios-plugins and net-mgmt/monitoring-plugins have a JAIL option which must be enabled for them to work correctly inside a jail.

15.6.4. Updating Jails Updating the Operating System

Because the basejail's copy of the userland is shared by the other jails, updating the basejail automatically updates all of the other jails. Either source or binary updates can be used.

To build the world from source on the host, then install it in the basejail, use:

# ezjail-admin update -b

If the world has already been compiled on the host, install it in the basejail with:

# ezjail-admin update -i

Binary updates use freebsd-update(8). These updates have the same limitations as if freebsd-update(8) were being run directly. The most important one is that only -RELEASE versions of FreeBSD are available with this method.

Update the basejail to the latest patched release of the version of FreeBSD on the host. For example, updating from RELEASE-p1 to RELEASE-p2.

# ezjail-admin update -u

To upgrade the basejail to a new version, first upgrade the host system as described in Section 24.2.3, “Performing Major and Minor Version Upgrades”. Once the host has been upgraded and rebooted, the basejail can then be upgraded. freebsd-update(8) has no way of determining which version is currently installed in the basejail, so the original version must be specified. Use file(1) to determine the original version in the basejail:

# file /usr/jails/basejail/bin/sh
/usr/jails/basejail/bin/sh: ELF 64-bit LSB executable, x86-64, version 1 (FreeBSD), dynamically linked (uses shared libs), for FreeBSD 9.3, stripped

Now use this information to perform the upgrade from 9.3-RELEASE to the current version of the host system:

# ezjail-admin update -U -s 9.3-RELEASE

After updating the basejail, mergemaster(8) must be run to update each jail's configuration files.

How to use mergemaster(8) depends on the purpose and trustworthiness of a jail. If a jail's services or users are not trusted, then mergemaster(8) should only be run from within that jail:

Example 15.1. mergemaster(8) on Untrusted Jail

Delete the link from the jail's /usr/src into the basejail and create a new /usr/src in the jail as a mountpoint. Mount the host computer's /usr/src read-only on the jail's new /usr/src mountpoint:

# rm /usr/jails/jailname/usr/src
# mkdir /usr/jails/jailname/usr/src
# mount -t nullfs -o ro /usr/src /usr/jails/jailname/usr/src

Get a console in the jail:

# ezjail-admin console jailname

Inside the jail, run mergemaster. Then exit the jail console:

# cd /usr/src
# mergemaster -U
# exit

Finally, unmount the jail's /usr/src:

# umount /usr/jails/jailname/usr/src

Example 15.2. mergemaster(8) on Trusted Jail

If the users and services in a jail are trusted, mergemaster(8) can be run from the host:

# mergemaster -U -D /usr/jails/jailname


After a major version update it is recommended by sysutils/ezjail to make sure your pkg is of the correct version. Therefore enter:

# pkg-static upgrade -f pkg

to upgrade or downgrade to the appropriate version. Updating Ports

The ports tree in the basejail is shared by the other jails. Updating that copy of the ports tree gives the other jails the updated version also.

The basejail ports tree is updated with portsnap(8):

# ezjail-admin update -P

15.6.5. Controlling Jails Stopping and Starting Jails

ezjail automatically starts jails when the computer is started. Jails can be manually stopped and restarted with stop and start:

# ezjail-admin stop sambajail
Stopping jails: sambajail.

By default, jails are started automatically when the host computer starts. Autostarting can be disabled with config:

# ezjail-admin config -r norun seldomjail

This takes effect the next time the host computer is started. A jail that is already running will not be stopped.

Enabling autostart is very similar:

# ezjail-admin config -r run oftenjail Archiving and Restoring Jails

Use archive to create a .tar.gz archive of a jail. The file name is composed from the name of the jail and the current date. Archive files are written to the archive directory, /usr/jails/ezjail_archives. A different archive directory can be chosen by setting ezjail_archivedir in the configuration file.

The archive file can be copied elsewhere as a backup, or an existing jail can be restored from it with restore. A new jail can be created from the archive, providing a convenient way to clone existing jails.

Stop and archive a jail named wwwserver:

# ezjail-admin stop wwwserver
Stopping jails: wwwserver.
# ezjail-admin archive wwwserver
# ls /usr/jails/ezjail-archives/

Create a new jail named wwwserver-clone from the archive created in the previous step. Use the em1 interface and assign a new IP address to avoid conflict with the original:

# ezjail-admin create -a /usr/jails/ezjail_archives/wwwserver-201407271153.13.tar.gz wwwserver-clone 'lo1|,em1|'

15.6.6. Full Example: BIND in a Jail

Putting the BIND DNS server in a jail improves security by isolating it. This example creates a simple caching-only name server.

  • The jail will be called dns1.

  • The jail will use IP address on the host's re0 interface.

  • The upstream ISP's DNS servers are at and

  • The basejail has already been created and a ports tree installed as shown in Section 15.6.2, “Initial Setup”.

Example 15.3. Running BIND in a Jail

Create a cloned loopback interface by adding a line to /etc/rc.conf:


Immediately create the new loopback interface:

# service netif cloneup
Created clone interfaces: lo1.

Create the jail:

# ezjail-admin create dns1 'lo1|,re0|'

Start the jail, connect to a console running on it, and perform some basic configuration:

# ezjail-admin start dns1
# ezjail-admin console dns1
# passwd
Changing local password for root
New Password:
Retype New Password:
# tzsetup
# sed -i .bak -e '/adjkerntz/ s/^/#/' /etc/crontab
# sed -i .bak -e 's/; s/localhost.my.domain/dns1.my.domain dns1/' /etc/hosts

Temporarily set the upstream DNS servers in /etc/resolv.conf so ports can be downloaded:


Still using the jail console, install dns/bind99.

# make -C /usr/ports/dns/bind99 install clean

Configure the name server by editing /usr/local/etc/namedb/named.conf.

Create an Access Control List (ACL) of addresses and networks that are permitted to send DNS queries to this name server. This section is added just before the options section already in the file:

// or cause huge amounts of useless Internet traffic.

acl "trusted" {;

options {

Use the jail IP address in the listen-on setting to accept DNS queries from other computers on the network:

	listen-on	{; };

A simple caching-only DNS name server is created by changing the forwarders section. The original file contains:

	forwarders {;

Uncomment the section by removing the /* and */ lines. Enter the IP addresses of the upstream DNS servers. Immediately after the forwarders section, add references to the trusted ACL defined earlier:

	forwarders {;;

	allow-query       { any; };
	allow-recursion   { trusted; };
	allow-query-cache { trusted; };

Enable the service in /etc/rc.conf:


Start and test the name server:

# service named start
wrote key file "/usr/local/etc/namedb/rndc.key"
Starting named.
# /usr/local/bin/dig @ freebsd.org

A response that includes

;; Got answer;

shows that the new DNS server is working. A long delay followed by a response including

;; connection timed out; no servers could be reached

shows a problem. Check the configuration settings and make sure any local firewalls allow the new DNS access to the upstream DNS servers.

The new DNS server can use itself for local name resolution, just like other local computers. Set the address of the DNS server in the client computer's /etc/resolv.conf:


A local DHCP server can be configured to provide this address for a local DNS server, providing automatic configuration on DHCP clients.

All FreeBSD documents are available for download at https://download.freebsd.org/ftp/doc/

Questions that are not answered by the documentation may be sent to <freebsd-questions@FreeBSD.org>.
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