Jail types

Use iocell get type TAG to inspect the stored type. The current creation interface differs from older full/thin/base flag examples.

Basejail (default)

iocell create tag=myjail creates a basejail. Writable configuration/data live in its jail datasets; base directories are mounted read-only from a shared fetched release using nullfs(5). This is not a fully independent OS image. Keep the corresponding release available for startup and package operations.

Updating shared base files affects every jail using that release. A jail-root snapshot or rollback does not include that shared release dataset. Plan backups and maintenance accordingly.

Clone

Create a clone from an existing jail or template:

iocell clone source-tag tag=mycopy

Or select an existing root snapshot:

iocell clone source-tag@snapshot-name tag=mycopy

Its root dataset is a writable ZFS clone and depends on its source snapshot. iocell promote mycopy reverses the ZFS clone dependency; it does not make shared basejail release directories into private OS copies. Check native ZFS origins before removing source datasets. create -c is not supported.

Template

A stopped basejail can become a template using:

iocell set istemplate=yes source-tag

Use a safe dataset-component tag first. Templates are listed with iocell list -t and are not started automatically. Deploy a new jail with:

iocell clone template-tag tag=mynewjail

Convert back with iocell set istemplate=no template-tag. The stored UUID, tag, snapshots and child datasets are preserved. The old template=yes property is not the conversion interface. See How to create and use templates for guards and failure behavior.

Empty

iocell create -e tag=empty-test creates an empty filesystem/metadata structure, not a populated FreeBSD installation or a clone. Supply a compatible userland and appropriate startup commands before trying to run it. This is a foundation for custom setups, not a promise of support for an arbitrary guest OS.

Independent/full (legacy thick jail)

The code can operate on complete independent userlands, including legacy thickjail images and Git-backed full OS trees. A type label alone does not populate such a userland. Current create does not provide the old -t full-jail mode; -b, -c and base=... recipes are also obsolete.

Independent 14.5 to 15.1 userland upgrade was tested, but not every legacy image format or custom guest OS. Do not assume an exported basejail includes its shared release files; see Jail images and historical differential packages and Known limitations.