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pot installation guide

This is a guide to prepare your FreeBSD installation to use the pot jail framework.

root user

Many operations need root privileges. In this guide, we consider to be logged in as root


ZFS is mandatory, so if you don't know what it is or you don't have a ZFS pool, please consider to read this quick guide.

FreeBSD version

pot is usually developed on CURRENT, but it's mainly tested and used on 12.1. It should work also on 11.3, even if the kernel has to be rebuild, to activate VNET(9), via the VIMAGE option. If you want to use FreeBSD 11.3, please follow the instruction reported on the handbook to build a custom kernel with the VIMAGE option enabled.

Install pot

pot is available as package or port.

The suggested way is to install pot is to use the package:

# pkg install -y pot
All dependencies will be automatically installed, if not already installed.

If you want to install it using ports, you can

# cd /usr/ports/sysutils/pot
# make install clean

Build with ports

A dependency of pot, called potnet is written in Rust. If you install potnet via ports, the build dependencies will be built as well, and it can take really long time (depending on the power of you system, it could be several hours).

Enable the resource limit database

One really useful feature, needed to improve the isolation between jails, is the resource limit database. This feature is normally disabled (it seems it causes a performance penalty in previous FreeBSD versions), and it can be enabled only at boot. To do so:

# echo kern.racct.enable=1 >> /boot/loader.conf
# reboot
This settings will take effect at the next reboot.

Known issue

An issue with the vtnet driver can cause poor performance on the network card. If pot is installed on a VM based on vtnet, the following command avoids the performance penalty:

# echo hw.vtnet.lro_disable=1 >> /boot/loader.conf

This setting needs a reboot to take effect.

pot framework configuration

Under the folder /usr/local/etc/pot you'll find two files:

  • pot.default.conf
  • pot.conf

The pot.default.conf contains all the default values and it shouldn't be touched. All needed changes can be made in the pot.conf file. This configuration file provide already a brief explanation for all parameters, but here we go deep, explaining them one by one

File system parameters

pot is based on ZFS. In the configuration file, 2 parameters are used to let pot use your ZFS pool correctly.

POT_ZFS_ROOT (default zroot/pot)

This parameter is the ZFS dataset that will be used by pot to store whatever will be needed: jails file systems, bases, and so on. If the dataset doesn't exist, it will be created by the initialization command (See the last chapter).

POT_FS_ROOT (default /opt/pot)

This parameter is the mountpoint for the POT_ZFS_ROOT dataset. You shouldn't use a mountpoint that exists and contains file, otherwise the content will become unreachable.

POT_CACHE (default /var/cache/pot)

This parameter specifies the mountpoint of the dataset POT_ZFS_ROOT/cache. This dataset is used only to store pot images for the import and the preparecommand. The default value is the suggested one.

Network parameters

In order to use network types like alias, public-bridge or private-bridge, some configuration parameters are needed.

POT_EXTIF (default em0)

Currently, pot assumes that all the network traffic is going through one physical network interface. This parameter configures pot to use the specified network interface.

POT_EXTIF_ADDR (default empty)

0.12.0 In case the POT_EXTIF has multiple addresses, public-bridge and private-bridge setup will use the first not alias IPv4 address for NAT and redirection. The parameter POT_EXTIF_ADDR can be used to specify which IPv4 address (assigned to POT_EXTIF) is the one to be used for NAT and redirection.

POT_NETWORK_STACK (default ipv4)

0.11.0 This parameter configures the network stack that a pot will set when created. There are three possible values

  • ipv4 : all pots will use IPv4 only
  • ipv6 : all pots will use IPv6 only
  • dual : all pots will have dual stack support, both IPv4 and IPv6

As explained here, this variable is only used as default value when a pot is created or cloned and no specific option is provided..

POT_NETWORK (default

This parameter specifies the IPv4 address of you internal virtual network and is used by the public-bridge network type only. It's wise to choose a private network segment that doesn't conflict with your current network setup. The default address space is huge, however you can choose the network range that match your needs.

POT_NETMASK (default

This parameter specifies the netmask relative to the POT_NETWORK. Theoretically, the netmask can be derived from the POT_NETWORK. For now, this is not the case, so you have to provide a netmask consistent with the network specified in POT_NETWORK

POT_GATEWAY (default

This parameter specifies the IP address that will be used as default gateway in your internal virtual network. It has to be part of the network specified in POT_NETWORK and it will be used as default gateway for all pots attached to the internal virtual network (public-bridge network type).

POT_EXTRA_EXTIF (default empty)

In case your host has multiple network interfaces connected to multiple network segments, this option allows your pots to access those network segments. For example, let's say that you have 2 vlan interfaces, called vlan20 and vlan30.

  • vlan20 is configured as
  • vlan30 is configured as

To make those segments accessible, the configuration file should look like:

POT_EXTRA_EXTIF=vlan20 vlan30
Currently there is no way to use additional external interface for the network type alias. All other network types are supported

Network validation

If you want to check that your network configuration is valid, you can use the utility potnet:

# potnet config-check
This command will show only the errors.

Other parameters

POT_LOG_FACILITY (default local2)

0.10.4 Every time pot is invoked, its activity is logged via syslogd(8). By default, the facility used is local2, but this parameter can be used to change it.

Experimental parameters

There are other parameters that are used by some experimental features.

VPN support

If your host system is using a VPN to reach some network segments, you can add some parameters in order to be able to connect your internal virtual network to those networks

  • POT_VPN_EXTIF: the name of the network interface of the VPN software tunnel; default: tun0
  • POT_VPN_NETWORKS: a list of all network segments served by the VPN; default:

If you have multiple network segments, you have to list them all. For instance:


dns pot [DEPRECATED]

An experimental feature is to provide an internal dns service running in a pot attached to the internal virtual network. The dns is still a work in progress, however two parameters are already present for this feature:

  • POT_DNS_NAME: this parameter specifies the name of the pot that will run the dns; default => dns
  • POT_DNS_IP: this parameter specifies the IP (internal to the POT_NETWORK that the "dns pot" will have; default =>

Initialize the environment

The initialization of the environment will:

  • Create the ZFS datasets
  • Validate the network parameters
  • Configure pf(4) to be aware of the internal virtual network

If you are already using pf, I suggest to make a backup of you pf configuration file.

When ready, you can initialize the environment with the command (use the flag -v if you want a bit more of verbosity):

# cp /etc/pf.conf /etc/pf.conf.bak
# pot init -v

Initialize and test the internal virtual network

The internal virtual network is not always active, but it's automatically activated if a pot configured to use it get started. However, a command is provided to activate the virtual network:

# pot vnet-start

From your host, you can now ping the virtual network default gateway (always reachable from the host):

# ping

Remove the pot environment

In order to remove the pot from your system, a command is provided to make it easy:

# pot de-init
This powerful command will remove everything related to pot and it cannot be undone.

Even if not mandatory, it would be nice to know why you removed it. Please, consider to write a feedback email to pizzamig at FreeBSD dot org

  • What's wrong with pot?
  • What's the missing feature I really need?
  • How bad is to use it? How can it be more user-friendly?

Last update: 2021-02-07