After I upgraded NixOS from 24.11 to 25.05, all printers stopped working. I have 4 printers, all are on the local network, all are using IPP. Print dialogs were showing “Rejecting jobs” in GUI applications (Firefox, Chromium, xreader). I tried configuring them in the local CUPS (localhost:631), they would still fail to print or discard the print jobs. At some point, I removed all configured printers. Two printers would appear in the Printers tab anyway (those two are on WiFi like my NixOS system, the other two are on wired Ethernet on the same subnet). The printers would ignore all output.
I’ll save you more details, but I was able to find the problem. The printers that were added automatically had their connection set to file:///dev/null. I assumed that it was OK for IPP, apparently it’s not.
So the solution is:
- for every auto-added printer, select it in “Printers”, go to “Administration” → “Modify Printer”, select the appropriate entry from “Discovered Network Printers”, select “Generic” make, select “IPP Everywhere”.
- for missing printers, go to “Administration” → “Add printer” and do the same.
Apparently it’s a CUPS bug to add a printer with a wrong URI. CUPS should know the correct URI, that’s how the printer is discovered.
I don’t know for sure if the issue is caused by the NixOS 25.05 upgrade. Everything just worked on NixOS 24.11, so I never needed to delete printers in CUPS.