Before upgrading a Jail:

• Update the Jail to the latest Patch Release
• Take a Snapshot

Stop the Jail.

Open the Shell.

iocage upgrade name -r release

where:

• name is the plugin jail name; and
• release is the desired release to upgrade to.

Determine what Releases are available:

iocage fetch

returns:

[0] 11.2-RELEASE (EOL)
[1] 11.3-RELEASE (EOL)
[2] 11.4-RELEASE
[3] 12.0-RELEASE (EOL)
[4] 12.1-RELEASE

Upgrade Plex:

iocage upgrade PlexServer -r 12.1-RELEASE

When the upgrade is done, enter the jail:

sudo iocage console PlexServer

and run:

pkg update && pkg upgrade

returns:

Updating iocage-plugins repository catalogue...
iocage-plugins repository is up to date.
All repositories are up to date.
Updating iocage-plugins repository catalogue...
iocage-plugins repository is up to date.
All repositories are up to date.
Checking for upgrades (0 candidates): 100%
Processing candidates (0 candidates): 100%
Checking integrity... done (0 conflicting)
Your packages are up to date.

sudo iocage list

returns:

+-----+------------+-------+--------------+------+
| JID |    NAME    | STATE |   RELEASE    | IP4  |
+=====+============+=======+==============+======+
| 4   | PlexServer | up    | 12.1-RELEASE | DHCP |
+-----+------------+-------+--------------+------+

If this error is seen:

pkg: repository meta /var/db/pkg/FreeBSD.meta has wrong version 2

try:

pkg bootstrap -f