Just wanted to chime in that everything seems to work fine after upgrading to TrueNAS. Changed to the 12.0 train yesterday and have been updating all the jails to 12.1. You have 2 options, backup the needed files, destroy the iocage jail, and create it again or the long way by upgrading. These instructions just need to be updated a bit and using a 12.1-RELEASE. Here's how upgrade your jails after you've updated to TrueNAS:
Code:
iocage upgrade -r 12.1-RELEASE jailname
You'll get to the a part asking if things look right, type in y. You'll get to a part where it wants you to review things, just hit q until it continues the install. This takes close to an hour on my server.
Go into the jail and enter
Code:
pkg-static install -f pkg
and