I am really looking for help troubleshooting this as I realised after searching the forums and wiki that I don't even know what I should be searching for.
I use a variety of printers with my laptop depending on where I am. Some of these are networked. Some are USB. Some are virtual.
The problem is that CUPS does not realise when a printer is *not* available. This can then cause it to not realise that the same printer is now available somewhere else.
I am in my office. I plug in a USB printer which has two virtual printers (HP1320 and HP1320_hplip_hpijs). Everything is fine. I can print using HP1320. (This is my default but sucks for graphics.)
I unplug the USB printer but CUPS continues to show HP1320 as "ready and printing". Even if I pause and resume the queue in CUPS, it still claims it is "ready".
If I now plug it into a different USB port, printing fails. If I plug it back into the original USB port, I can print again.
I sleep the laptop, come home, wake it. CUPS still insists that both HP1320 and HP1320_hplip_hpijs have status Idle and that HP1320 is "ready to print".
In addition, it claims that my home networked printer is Idle even though I have not switched it on in at least a few weeks.
It does recognise that a USB printer in my second workplace is unavailable, though.
Basically, I get this:
▼ Queue Name ▼ Description Location Make and Model Status CUPS_PDF Virtual PDF Printer CyfrifiadurCFR Generic CUPS-PDF Printer Idle Dell_2330dn Dell 2330dn Laser Printer (Socket) Cartref CFR Dell 2330dn Laser Printer Idle HP1320 HP LaserJet 1320 series (HPLIP) Humanities 1.40 HP LaserJet 1320 series Postscript (recommended) Idle - "ready to print" HP1320_hplip_hpijs HP LaserJet 1320 series (HPLIP HPIJS) Humanities 1.40 HP LaserJet 1320 Series hpijs pcl3, 3.12.4 Idle HP_LaserJet_P3010_Series HP LaserJet P3010 Series Learn HP LaserJet P3010 Series Postscript (recommended) Paused - "Unplugged or turned off"
Of these printers only CUPS_PDF is actually available. The Dell is the networked printer but is off. The two HP1320 printers refer to the same USB device (office) and the last HP refers to a different USB printer (second workplace - I did not use this printer recently from this laptop).
This used to work a bit better than this. However, because my laptop has been rather sick, I haven't taken it to work in a while and so haven't used a USB printer in a while. (My printer at home is networked.) So I have absolutely no idea when it stopped working or what changes I might have made which might have caused it to stop working.
In case it is relevant, KDE's printer settings panel shows the same information as CUPS. However, I never actually configure printers this way - I always use the web interface or, sometimes, the command line.
I noticed that I no longer get a system tray icon thing for printing even when there are active print jobs. This used to appear automatically. Investigation proved that this had been disabled, though, so I doubt this is significant. (I suspect it is just a KDE-update-blip thing.)
So I looked through the wiki page on CUPS but most of the issues were to do with printers not being recognised rather than non-printers being recognised. I searched for USB but this turned up a lot of irrelevant hits. (I thought maybe it is some setting to do with monitoring of USB ports and might be only incidentally related to printers.) I cannot say there is nothing relevant about it but I could not find it. I then wondered whether it might be a udev problem and found instructions for making udev see a device as removable but this is not quite the problem, I don't think, since the printers are recognised when added.
I tried to check whether or not the printers were recognised when absent by the USB system but I am not sure what I am looking for in the output of lsusb -v which is rather overwhelmingly long. (But let me know if I should post this.)
I would be very grateful if somebody could point me to relevant documentation or suggest a useful search time I could try.