Problem with /dev/usb/lp0

Help
1

Hi, I’m relative new to nixos, and I have a problem…

I need /dev/usb/lp0 exposed, because a thermal printer.

I found a solution: deactivating cups, but also I’ve a Laser printer that works with cups…

So I can’t find the way to expose /dev/usb/lp0 without deactivating cups, anyone know a way to do it?

I’ve usblp en my kernelModules

boot.kernelModules = [ “kvm-amd” “usblp” ];

Thank you !

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2

What do you mean by expose, please?

3

I need /dev/usb/lp0 in my filesystem to echo to a thermal printer.

But when cups is active, I understand the usblp module is blacklisted, and /dev/usb/lp0 doen’t get created

So, there is a way to mantain cups and load usblp at the same time?

Thank you

PD Sorry about my english is not my first language.

4

Can’t you use your thermal printer through CUPS? You may need to add a driver package for it via services.printing.drivers, but I don’t know if most folks should be using the usblp module for anything these days.

5

Yes I can see it, but that’s not the point, I need to send commands directly to the printer.

Almost all thermal printer works that way, you send it ESC/POS commands directly to the printer, no driver required.

But also I have a “normal” laser printer what requires cups, so my problem is i can’t use in the same NixOS installation both printers.

6

Yes, but couldn’t you send those commands via the lp program (with -o raw) instead of writing them to /dev/usb/lp0?

7

Hi again, thank you for your time, but that not a posible solution, the driver don’t “speak” the same language of the printer.

I use the printer to print barcodes (hundreds of them). Thermals printers have a set of native commands in the printer (ESC/POS)

If I print “\x1b\x21\x3012345678” with the lp command prints exactly that

But echoing the same string to the printer directly prints a bardoce in code128 format, that represents the last 8 character of the string. Those escape character are the ESC/POS commands, for cups is a normal string.

I need to use usblp kernel module and cups at the same time… or a way to cups understand the ESC/POS commands, but i think is way easier the first, because is the default dehaviour in Arch what is I using right now in that PC for this reason (I like to use NixOS in all my computers)

8

That kernel module is indeed being blacklisted by the CUPS (NixOS) module:

# Cups uses libusb to talk to printers, and does not use the
# linux kernel driver. If the driver is not in a black list, it
# gets loaded, and then cups cannot access the printers. 
boot.blacklistedKernelModules = [ "usblp" ];

If this comment it still valid, it does really look like it’s not possible to use both at the same time.

EDIT: if you say you can just do so in Arch, then it may be that this is no longer true. Maybe try to override the blacklist with lib.mkForce.

1 Like
9

OK… now I see exactly what is the problem, I gonna try your solution, maybe that is there for some legacy problem (I hope).

THANK YOU !

1 Like
10

Indeed that was the solution, thank you again, the printer works fine echoing directly to /dev/usb/lp0 and through CUPS too