TrueNAS CORETrueNAS CORE Nightly Development Documentation
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As of TrueNAS CORE 13.3, this feature is untested and provided without support to the TrueNAS Community.

Users with a critical need to use containers or virtualization solutions in production should migrate to the tested and supported virtualization features available in TrueNAS SCALE. TrueNAS Enterprise customers can contact iXsystems to schedule a TrueNAS SCALE deployment. See CORE to SCALE Migrations for more information.

Jails are a lightweight, operating-system-level virtualization. One or multiple services can run in a jail, isolating those services from the host TrueNAS system. The main differences between a user-created jail and a plugin are that plugins are preconfigured and usually provide only a single service.

Why use a Jail instead of a VM? By default, jails run the FreeBSD operating system. These jails are independent instances of FreeBSD. The jail uses the host hardware and runs on the host kernel, avoiding most of the overhead usually associated with virtualization. The jail installs FreeBSD software management utilities so FreeBSD packages or ports can be installed from the jail command line. This allows compiling FreeBSD ports and installing FreeBSD packages from the command line of the jail.

It is important to understand that users, groups, installed software, and configurations within a jail are isolated from both the TrueNAS host operating system and any other jails running on that system.

The ability to create multiple jails offers flexibility regarding software management. For example, an administrator can choose to provide application separation by installing different applications in each jail, to create one jail for all installed applications, or to mix and match how software is installed into each jail.

Setting Jail Storage

You must create a data storage pool before using jails. Make sure the pool has enough storage for all of the intended jails. The Jails screen displays a message and the CREATE POOL button if a pool does not exist on the TrueNAS system.

If pools exist, but one is not chosen to use with jails or plugins, a dialog displays prompting you to choose a pool. Select a pool and click CHOOSE.

To select a different pool for jail and plugin storage, click the icon, then select a different pool from the dropdown list.

TrueNAS uses iocage for jail and plugin management. Jails and downloaded FreeBSD release files are stored in a dataset named iocage.

About the iocage Dataset

The iocage dataset, automatically uses the first pool that is not a root pool for the TrueNAS system. It should have at least 10 GiB of free space (recommended), and cannot be located on a share.

A defaults.json file contains the default settings used when a new jail is created. The file is created automatically when not already present. When the file is present but corrupted, iocage shows a warning and uses default settings from memory.

Each new jail installs into a new child dataset of the iocage dataset. For example, with the iocage/jails dataset in pool1, a new jail called jail1 installs into a new dataset named pool1/iocage/jails/jail1. Go to Storage > Pools, click on the iocage dataset to expand it, then click on Jails to see jail datasets added for a new a jail from the Jails wizard screen or for a plugin jail from the add plugin wizard screen.

FreeBSD releases are fetched as a child dataset into the /iocage/download dataset. This dataset is then extracted into the /iocage/releases dataset to use in jail creation. Go to Storage > Pools, click on the iocage dataset to expand it, then click on download to see releases added from the Jails wizard screen. You can then remove the dataset in /iocage/download without affecting the availability of fetched releases or an existing jail.

The iocage datasets on activated pools are independent of each other and do not share any data.

iocage jail configs are stored in /mnt/poolname/iocage/jails/jailname. When iocage is updated, the config.json configuration file is backed up as /mnt/poolname/iocage/jails/jailname/config_backup.json. You can rename the backup file to config.json to restore previous jail settings.

See Setting Up Jail Storage for more information on jail storage and mount points.

Creating Jails

TrueNAS has two options to create a jail, the jail Wizard or ADVANCED JAIL CREATION. The jail Wizard provides the simplest process to create and configure a new jail. The ADVANCED JAIL CREATION alternate method has every possible configurable jail option. See [Jails Screen](/core/uireference/jailspluginsvms/jailsscreens/ for more information on jails screens and configuration settings.

To add a new jail, go to Jails then click ADD. The Wizard opens. To access the advanced configuration option, click ADVANCED JAIL CREATION at the bottom of the Wizard screen. We recommend only advanced users with very specific use applications use this method to create a jail.

Enter a name for the jail. Names can contain letters, numbers, periods (.), dashes (-), and underscores (_).

Select the jail type. Default (Clone Jail) or Basejail. Clone jails are clones of the specified FreeBSD release. They are linked to that release, even if they are upgraded. Basejails mount the specified release directories as nullfs mounts over the jail directories. Basejails are not linked to the original release when upgraded.

Specify the release to use. Options are 12.4-RELEASE or 13.2-RELEASE. Jails can run FreeBSD versions up to the same version as the host TrueNAS system. Newer releases are not shown. Versions of FreeBSD are downloaded the first time they are used in a jail. Additional jails created with the same version of FreeBSD are created faster because the download is already completed.


Click Next to display the Configure Networking wizard screen with a simplified list of networking options.


Jail Supported Networking Options

Jails support several different networking solutions:

  • VNET adds a virtual network interface to the jail.

    This interface can select NAT, DHCP, or static jail network configurations. Since VNET provides the jail with an independent networking stack, it can broadcast an IP address, which is required by some applications.

  • NAT (Network Address Translation) uses the TrueNAS IP address and selects a unique port for the jail to use.

    VNET is required when NAT is selected.

  • DHCP Autoconfigure IPv4 sets the jail receive its IP address from a DHCP server.

Configure networking by entering values in either the IPv4 Address or IPv6 Address fields. You can configure any combination of these fields. Multiple interfaces are supported for IPv4 and IPv6 addresses. To add more interfaces and addresses, click ADD.

Setting IPv4 Default Router and IPv6 Default Router to auto automatically configures these values. You must select VNET to enable the IPv4 Default Router field. When manually configuring IP addresses and if no interface is selected, TrueNAS automatically assigns the given jail IP address to the current active interface of the host system.

You can configure a jail without network settings.

Selecting a proxy in the TrueNAS network settings also configures new jails to use the proxy settings, except when performing DNS lookups. Make sure a firewall is properly configured to maximize system security.

When pairing the jail with a physical interface, edit the network interface and select Disable Hardware Offloading. This prevents a network interface reset when the jail starts.
Additional VMware Requirements

Jail Networking

If you have installed TrueNAS in VMware, you need functional networking to create a jail.

For the jail to have functional networking, you have to change the VMware settings to allow Promiscuous, MAC address changes, and Forged Transmits.

Promiscuous ModeWhen enabled at the virtual switch level, objects defined within all portgroups can receive all incoming traffic on the vSwitch.
MAC Address ChangesWhen set to Accept, ESXi accepts requests to change the effective MAC address to a different address than the initial MAC address.
Forged TransmitsWhen set to Accept, ESXi does not compare source and effective MAC addresses.

Click NEXT to view a summary of the chosen jail options. Click SUBMIT to create the new jail. After a few moments, the new jail is added to the Jails screen list.

Advanced Jail Creation

From the Jails screen click on ADD to open the Wizard, then click on ADVANCED JAIL CREATION at the bottom of the screen to open the Advanced Jail Creation form.


Enter the jail name, type, and select the release just as in the Name Jail and Choose FreeBSD Release Wizard screen.

Enter the networking settings leave all blank to create the jail without networking.

Click on Jail Properties to enter the settings for a jail ruleset to follow, commands to run in the system or jail environment, add a jail user, set allow or deny SYSV IPC message, shared memory, or semaphore primitives. You can also add VNET interfaces and other jail settings on this screen.

Click on Network Properties to add interfaces, host names, domain names, and resolver addresses, disable IPv4 or IPv6 source address selection for the jail in favor of the primary IPv4 or IPv6 address of the jail (only available when the jail is not configured to use VNET). You can also set the IPv4 or IPv6 IP address to inherit or restrict access to all system addresses or stop the jail from using either IPv4 or IPv6 entirely. You can configure MAC address settings.

Click Custom Properties to add the priority for the jail at boot time, jail host ID, set up the jail as a template. You can add system host time to synchronize time between the jail and host, enabling ZFS jailing inside the jail, define a dataset to be jailed and to be fully handed over to a jail, enter a mount point for the jail_zfs_dataset, configure tun settings, and add other local host, IP host name, and IPV6 autoconfigure settings.

Click SAVE to add the jail and return to the Jails screen.

Creating a Jail without Networking

You can create a usable jail without any networking by entering only the required Jail Name, selecting the Jail Type, and Release. To create a jail without networking, leave all network checkboxes cleared and fields empty to initialize the jail without any networking abilities.

To add networking to the jail after creation, go to Jails, click the for the jail, then click Edit. Configure the network settings in the Basic Properties area when the jail needs to communicate over the local network or out to the internet.

If you are an experienced user you can access additional advanced configuration settings in the Network Properties, and Custom Properties sections.

For more information on the configuration screens, see Jails Screens.

Creating a Template Jail

A template jail is a jail using the basejails type and customized with other software that can efficiently create other jails with the same configuration.

To create a template jail go to Jails, click ADD then click ADVANCED JAIL CREATION at the bottom of the Wizard screen, then:

  1. Create a jail to use as a template.

    a. Enter a name for the jail template, select Basejail as the Jail Type, and select the release from the Release dropdown.

    b. Configure the other jail setting you want to save in the template.

    c. Click SAVE to create the template and add this jail to the iocage/templates folder and list of available releases.

  2. Start this new jail, then click Shell to install the custom software packages. See Installing Jail Software for more information on customizing your jail template.

  3. Click SAVE.

  4. Click Stop to stop the jail.

  5. Click Edit to open the Edit Advanced Jail Creation screen and make the jail a template.

    a. Click on Custom Properties to show that section, then select Template.

    b. Click Save.

The new template jail shows on the Releases dropdown list.

  1. Add a new jail from the template.

    a. Click ADD to open the Wizard.

    b. Enter a name, select Default (Clone Jail), then select the name of the template from the Releases dropdown list.

    c. Click NEXT to enter networking settings.

    d. Click NEXT to review your settings and if satisfied with the settings, click SUBMIT to add the jail.

    You can select the Advanced Jail Creation option if you want to enter any other advanced settings not included in the template.

You must use the ADVANCED JAIL CREATION screens to create the basejail you want to use as a template. If you use the Wizard to create the basejail, then edit it to make it a template, any new jails created from this template do not start.

Jails Articles