How to troubleshoot inconsistent printer problems?

I suppose the fact that the printer is not called specifically by a printer server (CUPS) is what could be the main issue.

Now, on the compatibility side of things I don't have good experience with Brother but IIRC I might have seen that there are some models that work just fine with free drivers.

You may try install the printer via the web browser, localhost:631 or via the Printer application in Control Center or Settings depending on your DE, about testing printing I find enough to print blank pages from LibreOffice Writer, some text editors might print headers or time stamps, but Writer won't, so is good when you only want to test connectivity.

Hope that makes sense, regards!

As an addendum, CUPS print server, which is also available in Trisquel's repositories, is responsible for taking a copy of a document that is to be printed and add it to a queue so the printer can adequately see it's entirety.

I see there are a some different ways to communicate with a network printer at http://localhost:631/admin/. At localhost:631, as mentioned, is where I find CUPS (had to give username and password for add printer function). I guess I can assume since I reach the CUPS page that it is installed and starts as a daemon automatically when I boot up. There is a cups driver at 'https://github.com/pdewacht/brlaser' and your printer is on a list there as supported. But there is also a version of 'brlaser' I see in our synaptic repository.

If in your shoes I think I would make sure each laptop has CUPS installed and brlaser on top of that for starters.

If you are way ahead of me, please don't be offended, from your post I don't know.

I am using an Epson ET-2800 and I see that it is installed in CUPS and I can see it in, for me, Preferences > Printers as well.

I was once kind of in your shoes and most of my printers were HP and most of the Workstations were the ones with Darth Vader operating systems. My printers were mostly connected via the router but some may have had their own wifi print server operating. I do not remember these things well, but I read that in the CUPS world, drivers are intended to go away being replaced with Internet Printing Protocol so you have several ways to try to hook up to your printer assuming you router is still allowing it.

I could be jealous that you are using Trisquel laptops at work. I could not talk anyone out of the 'evil empire' stuff. It seems like you'll figure out a solution.

I am familiar with the HL-L2390DW as my parents have it. It works with printer-driver-brlaser but the upstream version is unmaintained (though there is a maintained fork) so there hasn't been a release with that particular printer definition. However, it should work if you just manually add a printer with a slightly different number like HL-L2360D that uses the brlaser driver. I'm not sure about the HL-L2420DW but you can try the same thing and see if it works.

If you want to use the HL-L2390DW scanning, it will be available in a future version of SANE - some people including myself independently reverse engineered the scanning protocol (it's actually really simple). I wrote a standalone scanning program in C for my personal use, and I intended to contribute a backend to SANE but put it off for a while. Anyway it turned out that one of the SANE developers had written a backend for Brother scanners around the same time, and it works pretty well. I did provide some information about the protocol that he wasn't aware of.

Cool effort there Legimet. My Epson ET-2800 is not found by xsane. Hears hoping that gets added too.

I did try that. Online I found two different Vendor #s and no Device ID for this printer. I did find another ecotank style device and tried that. However running xsane from the terminal produced a message that that line couldn't be parsed. I also found some info that libusb was required and I made sure I had that. I found an epson ipp download in our repository. Somehow, I broke the printer. Cups said it was waiting for it to come online. I changed it to the 'driverless' IPP mode. Now it is printing again and xsane finds it and can scan. The quality of the scan is poor. A page with color came out greyscale I guess. And somewhat faint. But at least progress.

So like
Bus 002 Device 003: ID 04b8:1187 Seiko Epson Corp. ET-2800 Series
I think would be
usb 0x04b8 0x1187
in /etc/sane.d/epsonds.conf? Do I need these, <>?

I appreciate your help.

Thanks again Legimet and Thanks Jacob K for starting the thread, hope he solved that issue.

When I run sudo systemd-hwdb update

I get

/etc/udev/hwdb.d/20-epson-scanner.hwdb:4: Property expected, ignoring record with no properties.
/etc/udev/hwdb.d/20-epson-scanner.hwdb:5: Property expected, ignoring record with no properties.

scanimage -L gets
'Could not find command-not-found database. Run 'sudo apt update' to populate it.
scanimage: command not found'

I did "Run 'sudo apt update' "
didn't help, no scanimage

in xsane Preferences > Enable Color Management I get a message box announcing
"Error durine CMS conversion:
Could not open scanner ICM profile"

I tried 'locate ICM or icm I do see
/usr/src/linux-headers-5.15.0-126/drivers/iio/imu/inv_icm42600
/usr/src/linux-headers-5.15.0-126/drivers/iio/imu/inv_icm42600/Kconfig
/usr/src/linux-headers-5.15.0-126/drivers/iio/imu/inv_icm42600/Makefile
Don't know if that's relevant.

When I call for xsane in the terminal:
'~$ xsane

(xsane:5653): Gtk-WARNING **: 09:33:18.595: Unable to locate theme engine in module_path: "pixmap"'

However, something, perhaps checking Enable Color Management and then unchecking it, or changing a setting from lineart to Gray did improve the quality of the scan. I think it looks fine now - just no color.

So that is a real big improvement from no scan at all. I seldom need color anyway.

The format of /etc/udev/hwdb.d/20-epson-scanner.hwdb needs to be precise. When I copy and paste it from my post, I actually get blank lines in between so I'm guessing this is what happened in your case. The first line starting with '#' is a comment. The second line "usb:v04B8p1187*" needs to be followed immediately by the third line. And the third line needs to start with exactly one space, so " libsane_matched=yes".

Fix that file and run "sudo systemd-hwdb update" again.

scanimage is in the package sane-utils. Just a tip, you can use "apt-file search" to search for packages containing a file.

Printing completely blank pages from LibreOffice Writer after adding the printer manually seems to work fine, but there's a "cups-waiting-for-job-completed" error while it's printing.

I didn't have to install any custom packages, and the driver says "Brother HL-L2390DW, driverless, cups-filters 1.28.15 (grayscale, 2-sided printing)".

Printing from Abrowser goes to the queue, but for some reason it's much slower to start printing. After around 5 minutes it said "Processing page 25..." by the job at http://localhost:631/jobs?which_jobs=all (but I don't see a way to get that info from the queue view in the Printers Administration application, or any way to show that info on the bottom panel.

Actually, it seems like the job from Abrowser timed out eventually. It says it completed 10 minutes after it started, but no paper came out of the printer. The document was 30 pages, and it seemed like it finished "processing" around 6 minutes in, but then pages did not start printing for some reason.

Atril finishes the "processing step" in less than a minutes, and then the printer starts making noise as soon as that's finished. This time, it printed all 30 pages (on 15 sheets).

Yes, now
sudo systemd-hwdb update
tardies a moment and the returns with no error.

OK ... after installing sane-utils

scanimage -L
device `escl:http://localhost:60000' is a Epson ET-2800 Series (USB) platen scanner
device `epsonds:libusb:002:003' is a Epson PID 1187 ESC/I-2

Just for fun - Abrowser directed to that port gets
This address is restricted

This address uses a network port which is normally used for purposes other than Web browsing. Abrowser has canceled the request for your protection.