2023-06-29

Trouble using a venerable HP Laserjet 1020 in CUPS in RHEL 9.2. 
With all hplip stuff installed, 
	hplip-common-3.21.2-6.el9.alma.x86_64
	hplip-libs-3.21.2-6.el9.alma.x86_64
	hplip-3.21.2-6.el9.alma.x86_64
the autosetup found the printer, but nothing came out: filter failed (I think that was the message). 

Measures trying to correct "included but not limited to" installing foomatic-db{,-ppds}, getting 
and trying the driver foo2zjs-z1.ppd instead of HP's own, installing foo2zjs (from git) and putting 
some of its executables wanted by this ppd into first /usr/bin and then another place apparently 
searched by the binary /usr/lib/cups/filter/foomatic-rip (which was complaining about not finding 
other programs it needed), and a bit more, then restarting cups many times, replugging the printer, 
changing the usb cable, ...  Much of 
 killall cupsd
 systemctl restart cups
 journalctl -u cups -e

Then on trying the HP driver (hpcups .ppd) again, looking at the logs with more care, 
seeing it's not able to talk with the printer.  This gave a little clue about permissions. 
First tried selinux denials, but this didn't look relevant. 

What *seems* to have been the cause of its starting working was simply to give suitable 
permissions on the usb device:

# lsusb     (find printer, use the two numbers from start of line: bus, device)
 
# chmod a+rw /dev/bus/usb/001/096     (end part is bus/device for the printer, from lsusb)

# systemctl restart cups 

Then all was well. 
To make this permanent one could change the group that the CUPS part is running under, 
or change the usb plugging owner/permission settings, or just keep on giving everyone the permission...