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Antranig Vartanian e86a7c17ff
PR #9: Better init, DHCP support, new rc.d/jail and more!
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NOTE: This README is just a complete guide. We'd like your help to write manual pages :)

Jailer is heavily under development and not yet ready for production use. The interface is subject to refinement and change, but you are more than welcome to use it and help us improve it with your invaluable feedback. It does not mean you cannot use it in production, though. Just beware that a lot might change in time.

However, that being said, we do use it in our production to manage servers and in our products.

Jailer is a modern, minimal, flexible, and easy-to-expand FreeBSD Jail manager built with love by experienced users for both neophytes and experts.


Jailer is not in FreeBSD ports yet, you need to install it manually

git clone
cd jailer
make install


  • FreeBSD
  • ZFS

Jailer is so much attached to ZFS and does not support UFS at this time (and most likely it will never do.) In case you are not using ZFS, you can create a ZFS pool by doing something like the following:

truncate -s 20G /usr/local/disk0.img
zpool create zroot /usr/local/disk0.img

Setup and Initialization

Custom Jail Service file

At the moment we use a custom rc.d/jail file, which is sent to FreeBSD as D38826: Fix multiple rc.d/jail and jail.conf.d issues. Once it's merged, we wont patch rc.d/jail anymore (unless we do more changes). jailer init will handle the patches.

Once the environment meets the basic requirements, Jailer initialization is required. all you need to do is the following:

jailer init

Here's how it looks like →

root@armbsd13:~ # jailer init
Jailer will create
 dataset     : zroot/jails
 mount point : /usr/local/jails
OK? (y/N) y
Creating ZFS dataset zroot/jails with the mount point /usr/local/jails: Done!
Setting jailer_dir in rc.conf: Done!
Enabling the jail service: Done!
Patching jail service for jail.conf.d support: Done!

You may run `jailer init info` to check system status
You may run `jailer init bridge` to setup advanced networking

Please report any problems at
The latest information about Jailer is available at
Consider joining Jailer's worldwide community:

Thank you for choosing Jailer!

Or, if you like colors, here's a picture :)


Basic Usage

At this point, you can create a Jail

jailer create

You should get the following →

root@armbsd13:~ # jailer create
Fetching 13.1-RELEASE: Done!
Creating 99d6c13c: Done!

By default, Jailer will fetch a base image if it's not available. You can list all images by doing

root@armbsd13:~ # jailer image list

Fetching might take a while, if you know a mirror that's closer to you, you can set the FreeBSD_mirror variable to that. e.g. setenv FreeBSD_mirror "" with tcsh or export FreeBSD_mirror="" with /bin/sh

You can list and download other images as well

root@armbsd13:~ # jailer image list remote
root@armbsd13:~ # jailer image fetch 13.0-RELEASE
Fetching 13.0-RELEASE: Done!

To list all the Jails, you can do jailer list. You should get the following →

root@armbsd13:~ # jailer list
NAME      STATE   JID  HOSTNAME           IPv4  GW
99d6c13c  Active  7    99d6c13c.armbsd13  -     -

This means that Jail 99d6c13c is using an inherited network stack, which is NOT SECURE for production use. In the next part, we will configure Jails with restricted and isolated network stacks.

Restricted networking on an external interface

You can attach your Jail to an external interface as well. To attach a Jail to the interface vtnet0 with the IP address you can do the following →

root@armbsd13:~ # jailer create -t new -b vtnet0 -a www0
Creating www0: Done!
root@armbsd13:~ # jailer list
NAME      STATE   JID  HOSTNAME           IPv4           GW
99d6c13c  Active  7    99d6c13c.armbsd13  -              -
www0      Active  9    www0.armbsd13  -

Unlike 99d6c13c, which has an inherited network stack, the Jail www0 has a restricted network stack, we can see that by logging into the Jail and running ifconfig

root@armbsd13:~ # jailer console www0
root@www0:~ # ifconfig 
vtnet0: flags=8863<UP,BROADCAST,RUNNING,SIMPLEX,MULTICAST> metric 0 mtu 1500
	ether 52:88:80:9b:bb:00
	inet netmask 0xffffffff broadcast
	media: Ethernet autoselect (10Gbase-T <full-duplex>)
	status: active
lo0: flags=8049<UP,LOOPBACK,RUNNING,MULTICAST> metric 0 mtu 16384
	groups: lo

The Jail www0 is not aware of any other IP addresses, but can see the network interfaces. It also has the same networking that's available on the host's vtnet0 interface. If the host has internet access, so does www0

root@www0:~ # ping -c 1
PING ( 56 data bytes
64 bytes from icmp_seq=0 ttl=57 time=44.368 ms

Advanced Networking

Jailer can auto-configure the host to have advanced networking. We can check the status by running the following

root@armbsd13:~ # jailer init info
Checking system state...
 jail_enable in rc.conf  ==> YES!
 patched rc.d/jail file  ==> YES!
Checking jailer state...
 jailer_dir in rc.conf   ==> YES!
 jailer_dir is define to ==> zfs:zroot/jails
 Jailer ZFS dataset      ==> zroot/jails
 Jailer ZFS mountpoint   ==> /usr/local/jails
Checking network status...
 bridge0 in rc.conf      ==> NO :(
  If you want Jailer to auto-configure bridge interfaces, run `jailer init bridge`

We can run jailer init bridge to setup internal bridge networking between Jails and the host

Jailer will configure
 network interface : bridge0
 network address   :
OK? (y/N) y
Configuring interface bridge0 with IP address Done!

You may run `jailer init dhcp` to setup DHCP server for bridge0

At this point, we can run a VNET (Virtualized Network) Jail that uses an epair to attach to bridge0 (we call that an eb Jail for epair/bridge)

root@armbsd13:~ # jailer create -t eb -a
Creating fd1dafdc: Done!
root@armbsd13:~ # jailer list
NAME      STATE   JID  HOSTNAME           IPv4           GW
99d6c13c  Active  7    99d6c13c.armbsd13  -              -
fd1dafdc  Active  11   fd1dafdc.armbsd13
www0      Active  9    www0.armbsd13  -

To assign IPs automatically on VNET interfaces, you can setup a DHCP server. No worries! Jailer can handle that for you as well! It will install OpenBSD's dhcpd, setup dhcpd.conf and the needed devfs.rules for Jails.

root@armbsd13:~ # jailer init dhcp
Jailer will
 - Install OpenBSD's dhcpd from packages.
 - Setup dhcpd.conf.
 - Create /etc/devfs.rules for VNET Jails.
OK? (y/N) y
Setting up dhcpd, dhcpd.conf and devfs.rules: Done!

Now you can create a VNET Jail that uses DHCP.

root@armbsd13:~ # jailer create -t eb app0
Creating app0: Done!
root@armbsd13:~ # jailer list
NAME      STATE   JID  HOSTNAME           IPv4           GW
99d6c13c  Active  7    99d6c13c.armbsd13  -              -
app0      Active  12   app0.armbsd13
fd1dafdc  Active  11   fd1dafdc.armbsd13
www0      Active  9    www0.armbsd13  -

As you have guessed, if -a address is not assigned, then Jailer defaults to -a dhcp :)

If your VNET Jails need internet access, you probably need to setup NAT. Here's the easiest way to do that

# Enable routing
echo 'net.inet.ip.forwarding=1' >> /etc/sysctl.conf
service sysctl restart
# Enable pf
sysrc pf_enable="YES"
# Get default interface
default_interface=$(route get default | grep interface | cut -w -f 3)
# Generate the configuration and start pf
echo "nat on $default_interface from to any -> ($default_interface)" >> /etc/pf.conf
service pf start

If you get a message that says Illegal variable name then you're probably using tcsh. You can jump into /bin/sh by running sh :)

Jailer has the nat and rdr subcommands to manage NAT and Redirection, but it will be integrated in the next release.

Now, you can login into your VNET Jail and access the internet.

root@armbsd13:~ # jailer console app0
root@app0:~ # host -t A has address

Stopping and Destroying Jails

To stop a Jail

root@armbsd13:~ # jailer stop www0
Stopping www0: Done!

To stop all Jails

root@armbsd13:~ # jailer stopall
Stopping jails: 99d6c13c fd1dafdc app0.

And to start all

root@armbsd13:~ # jailer startall
Starting jails: 99d6c13c app0 fd1dafdc www0.

To destroy a Jail

root@armbsd13:~ # jailer destroy www0
Destroying www0: Done!

If you get an error message that says resource is busy, then it probably is. You can force destroy by doing jailer destroy -f jailname.

Snapshots and Clones

ZFS Snapshots are some of its best features. You can snap a Jail to 1) rollback in case something fails 2) create a new Jail base on it.

Create a snapshot of app0 named prod

root@armbsd13:~ # jailer snap app0@prod
Taking the snapshot app0@prod: Done!

Create a Jail named app01 from app0@prod

root@armbsd13:~ # jailer create -t eb -s app0@prod app01
Creating app01: Done!

In the coming releases, Jailer will have the ability to deploy ZFS Clones as well, which would allow you to save storage space.

Default Values

Default Image/Release

To specify an image as default, you can use the image use subcommand →

root@armbsd13:~ # jailer image list
root@armbsd13:~ # jailer image use 13.1-RELEASE
root@armbsd13:~ # jailer image list
* 13.1-RELEASE

Otherwise, you can use the -r imagename flag to create a Jail based on imagename on the fly.

Default Network Type

As mentioned above, it's not a good idea to use inherited network stack on production. You can specify the default network type with the network use subcommand

root@armbsd13:~ # jailer network use eb
root@armbsd13:~ # jailer network use

Dry run

Jailer can display all the commands it would run during creation by using the -D flag.

root@armbsd13:~ # jailer create -D db0
jail.conf file =>
# vim: set syntax=sh:

db0 {
  $id             = "6";
  devfs_ruleset   = 10;
  $bridge         = "bridge0";
  $domain         = "armbsd13";
  vnet.interface = "epair${id}b";

  exec.prestart   = "ifconfig epair${id} create up";
  exec.prestart  += "ifconfig epair${id}a up descr vnet-${name}";
  exec.prestart  += "ifconfig ${bridge} addm epair${id}a up";

  exec.start      = "/sbin/ifconfig lo0 up";
  exec.start     += "/bin/sh /etc/rc";

  exec.stop       = "/bin/sh /etc/rc.shutdown jail";
  exec.poststop   = "ifconfig ${bridge} deletem epair${id}a";
  exec.poststop  += "ifconfig epair${id}a destroy";

  host.hostname   = "${name}.${domain}";
  path            = "/usr/local/jails/db0";
  exec.consolelog = "/var/log/jail/${name}.log";
ZFS commands =>

  (zfs send zroot/jails/image/13.1-RELEASE@base |
   zfs recv zroot/jails/db0)

Resolver commands =>
  cp /etc/resolv.conf /usr/local/jails/db0/etc/resolv.conf
Network setup commands =>
  echo "ifconfig epair6b ether 58:9c:fc:a1:8a:3a" > /usr/local/jails/db0/etc/start_if.epair6b
  sysrc -q -f /usr/local/jails/db0/etc/rc.conf ifconfig_epair6b="SYNCDHCP"
Post-Installation =>
  sysrc -q -f /usr/local/jails/db0/etc/rc.conf sendmail_enable="NONE" syslogd_flags="-ss"

JSON Output

Some subcommands support JSON output.

root@armbsd13:~ # jailer list -j | jq
    "name": "99d6c13c",
    "state": "Active",
    "jid": "21",
    "hostname": "99d6c13c.armbsd13",
    "ipv4": "-",
    "gateway": "-"
    "name": "app0",
    "state": "Active",
    "jid": "22",
    "hostname": "app0.armbsd13",
    "ipv4": "",
    "gateway": ""
    "name": "app01",
    "state": "Active",
    "jid": "25",
    "hostname": "app01.armbsd13",
    "ipv4": "",
    "gateway": ""
    "name": "fd1dafdc",
    "state": "Active",
    "jid": "23",
    "hostname": "fd1dafdc.armbsd13",
    "ipv4": "",
    "gateway": ""
    "name": "www0",
    "state": "Active",
    "jid": "24",
    "hostname": "www0.armbsd13",
    "ipv4": "",
    "gateway": "-"


You are more than welcome to contribute to Jailer, whether it is on code, doc, or just to fix a typo. Please open an issue if you find a bug, or a PR if you have fixed one. All code changes must be reviewed and tested.


In January of 2021, @antranigv and @riks-ar had a bet whether @antranigv is able to rewrite @illuria's ZFS, Jail and ifconfig(8) wrappers from Elixir to Shell. The deal was if @antranigv failed to do that in 2 weeks, then @riks-ar gets @antranigv's desk and chair (which was the best one in the office at the time). If @antranigv succeeded, then he had the right to open-source the Shell program at any time in the future.

On October 20th 2022, @illuria open-sourced Jailer by pushing the code to this repository :)