It turns out omshell on Debian (11), Ubuntu 20.04 and 22.04 is broken.
I added the omapi key to ISC and Foreman-proxy, just in case. This resolved the omshell errors reported, but things still didn’t work. Then I found these links about omshell:
- Foreman-proxy ISC dhcpd - #2 by lzap
- #995242 - isc-dhcp-server: omshell returns inconsistent results or segfaults - Debian Bug report logs
- Comment #18 : Bug #1916931 : Bugs : isc-dhcp package : Ubuntu
Replacing the Ubuntu default version of omshell (v4.4.1) with v4.4.3 fixed the issue for me. I used the instructions from the last link (post 18 of the Launchpad bug report).