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pot as thick jail

Introduction

A thick jail is a jail that doesn't exploit the base/package separation that FreeBSD provides, but put all the needed files in one file system.

In pot, a thick jail is a jail composed by only one ZFS dataset and is called pot of type single (as single ZFS dataset)

Thick jails have advantages and disadvantages that has to be evaluated before the jail is created. Once adopted a type, pot doesn't provide yet a way to convert jails from one type to another.

Create a thick jail

The following command creates a pot of type single:

# pot create -p casserole -b 12.1 -t single

In detail:

  • -p casserole : the name of the pot
  • -b 12.1 : the version of FreeBSD to use to create the jail
  • -t single : the pot type (single ZFS dataset)

The create command will:

  • fetch the FreeBSD base tarball (if not already cached)
  • extract the tarball

Note

The FreeBSD base tarball doesn't contain any security updates. A flavour is provided to run the update during the creation:

# pot create -p casserole -b 12.1 -t single -f fbsd-update

Use the thick jail

In common with all pots, several commands are available to thick jails:

# pot info -vp casserole     # to show information about the pot
# pot start casserole        # to start the pot
# pot show -p casserole      # to show run-time information about the pot
# pot term casserole         # to open a shell in the pot
# pot run casserole          # to start and open a shell in the pot [start+term]
# pot stop casserole         # to stop the pot

Additional features

Because their internal structure is easier to manage, thick jails provide additional features, that are not available for thin jails

Export a pot as image

A pot image is a snapshot of the ZFS dataset stored in a compressed file. Technically, a snapshot of a pot is exported in a file, not the pot itself.

A snapshot can be taken with the commands:

# pot stop casserole # if the pot is running
# pot snapshot -p casserole
# pot purge-snapshot -p casserole

More information about snapshots are available in the dedicated Snapshot section.

When a snapshot is available, an image of the snapshot can be exported:

# pot export -p casserole -t 1.0
In detail:

  • -p casserole : the name of the pot
  • -t 1.0 : the tag, a label that can be used for versioning

The output is two files:

# ls
casserole_1.0.xz
casserole_1.0.xz.skein

The casserole_1.0.xz file is the image and contains the filesystem of the pot, while the casserole_1.0.xz.skein file is just a hash

Compression performance

The compression utility chosen is xz(1) that provides high compression ratio, but it can be a bit slow. xz(1) is configured to run in parallel using as many core as possible. If you are running pot in a VM, you can consider to add more CPU core to speed up the compression process

Import a pot from an image

The opposite operation of export is import.

As example, the casserole image can be imported from the local directory with the command:

# pot import -p casserole -t 1.0 -U .

In detail:

  • -p casserole : the name of the pot
  • -t 1.0 : the tag, a label that can be used for versioning
  • -U . : the URL where to look for the image; in this case, the local folder (.)

The pot is imported with the name casserole_1_0.

# pot ls -q
casserole_1_0
casserole

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