Printing

Basic configuration

Add to /etc/nixos/configuration.nix:
```
{
  ...
  services.printing.enable = true;
  services.printing.drivers = [ YOUR_DRIVER ];
  ...
}
```
where YOUR_DRIVER is the driver package appropriate for your printer. Commonly used driver packages include:
- pkgs.gutenprint — Drivers for many different printers from many different vendors.
- pkgs.gutenprintBin — Additional, binary-only drivers for some printers.
- pkgs.hplip — Drivers for HP printers.
- pkgs.hplipWithPlugin — Drivers for HP printers, with the proprietary plugin. Use
```
nix run nixpkgs.hplipWithPlugin -c sudo hp-setup
```
  to add the printer, regular CUPS UI doesn't seem to work.
- pkgs.samsungUnifiedLinuxDriver — Proprietary Samsung Drivers
- pkgs.splix — Drivers for printers supporting SPL (Samsung Printer Language).
- pkgs.brlaser — Drivers for some Brother printers
- pkgs.brgenml1lpr and pkgs.brgenml1cupswrapper — Generic drivers for more Brother printers [1]
- pkgs.cnijfilter2 — Drivers for some Canon Pixma devices (Proprietary driver)
- Some printers might be supported by built-in CUPS drivers.
- Search for other printer drivers in the NixOS package directory: the official list of packages is here but does not list unfree packages (which is the case of many printer drivers). To list unfree packages, see The appropriate FAQ entry for installing unfree packages.
(Add the driver to services.printing.drivers, not environment.systemPackages.)
Rebuild:
```
$ sudo nixos-rebuild switch
```
CUPS will be started automatically.
Navigate to http://localhost:631/ in a web browser to configure printers. Alternatively, some desktop environments may provide GUI interfaces for adding printers, for example system-config-printer.

You may need to authenticate when you add the printer. Search the web for e.g. “cups add printer” for further information.

With a raw PPD

If no driver is found for your printer, even when services.printing.drivers is correctly populated (see above), you can try to give cups a PPD file.

Download the required PPD file, for example from openprinting.org
Open the PPD as a text file, and check that it does not mention FHS paths like /usr/bin. If it does, this method is unlikely to work, as the PPD file depends on executables not present on your system.
add the printer with system-config-printer (for example) and at the 'choose driver' screen choose 'provide PPD file'

Networked printers

In some cases (e.g.: the Brother HL-3170CDW), you don't even need drivers or a PPD file. Simply open up the CUPS dashboard, add a printer at ipp://your-printer-ip, and make sure to select the "IPP Everywhere" driver.

Setting up shared printers

Server

If you want to share a local printer on the network, follow the steps in Basic Configuration, but check “Share This Printer” when adding it to CUPS. If you have already added the printer to CUPS, reconfigure it to make it a shared printer.
You should probably check that printing works locally at this point.

Amend /etc/nixos/configuration.nix:

{
  ...

  # Enable automatic discovery of the printer from other Linux systems with avahi running.
  services.avahi.enable = true;
  services.avahi.publish.enable = true;
  services.avahi.publish.userServices = true;
  services.printing.browsing = true;
  services.printing.listenAddresses = [ "*:631" ]; # Not 100% sure this is needed and you might want to restrict to the local network
  services.printing.allowFrom = [ "all" ] # this gives access to anyone on the interface you might want to limit it see the official documentation
  services.printing.defaultShared = true; # If you want

  networking.firewall.allowedUDPPorts = [ 631 ];
  networking.firewall.allowedTCPPorts = [ 631 ];

  ...
}

Rebuild:
```
$ sudo nixos-rebuild switch
```

Note: I think I had to check "Share printers connected to this system" and "Allow printing from the internet" at http://192.168.11.9:631/admin but I'm not sure.

This article or section is out of date.

Reason: Needs checking to rectify uncertainty in instructions (Discuss in Talk:Printing)
Once the page has been updated this notice can be removed.

Client (Linux)

If you want to use a printer shared on the network, and if you enabled services.avahi.publish.userServices in the server configuration, enabling printing and avahi on the client should be sufficient for the printer to be detected:

{
  ...
  services.printing.enable = true;
  services.avahi.enable = true;
  # Important to resolve .local domains of printers, otherwise you get an error
  # like  "Impossible to connect to XXX.local: Name or service not known"
  services.avahi.nssmdns = true;
}

If CUPS complains about "Impossible to connect to XXX.local: Name or service not known" even if services.avahi.nssmdns is enabled as shown above, the reason could be that mdns does not work properly with IPv6 in your network. In such a case, switching to mdns4-only setup can help:

{
  ...
  services.avahi.nssmdns = false; # Use the settings from below
  # settings from avahi-daemon.nix where mdns is replaced with mdns4
  system.nssModules = with pkgs.lib; optional (!config.services.avahi.nssmdns) pkgs.nssmdns;
  system.nssDatabases.hosts = with pkgs.lib; optionals (!config.services.avahi.nssmdns) (mkMerge [
    (mkOrder 900 [ "mdns4_minimal [NOTFOUND=return]" ]) # must be before resolve
    (mkOrder 1501 [ "mdns4" ]) # 1501 to ensure it's after dns
  ]);
}

See this bug report for details.

Troubleshooting

Upgrade Required

Described in: Github issue 23993
Problem
Using the cups web interface, the page tells you "Upgrade Required" and then redirects you to a page that fails to load.

Cause
When you are using http and cups wants authentication it will redirect you to a https version by default.
In order to use https it needs ssl keys. However it is possible that cups fails to generate these keys, and then the page will fail to load.

Solution
Either we can help cups to get ssl keys, or we can tell it to not use https at all.
Generating ssl keys:
First make sure the directory /etc/cups/ssl exists:
sudo mkdir -p /etc/cups/ssl
Try restarting cups and using the web interface again. This might be enough to get it working.
If this didn't help, then check if cups has generated ssl keys in /etc/cups/ssl
Disabling ssl:
Edit your /etc/nixos/configuration.nix and add the following lines:

services.printing.extraConf = ''
    DefaultEncryption Never
  '';

Unable to launch Ghostscript: gs: No such file or directory

Described in: Github issue 20806 and issues 22062
Problem
When printing, cups will report an error: Unable to launch Ghostscript: gs: No such file or directory

Cause
Some drivers use the ghostscript binary.
Cups will look for the binary path in it's config file: cupsd.conf
This file is normally a link. But it can be overwritten, and consequentially become outdated.

Solution
You could try to manually fix the path variable in /var/lib/cups/cupsd.conf
Alternatively you could try to delete the file and run sudo nixos-rebuild switch

File is missing (Gnome 3)

When you add an printer in Gnome (using gnome-control-center printers) you create a profile for your printer.

Problem
But, later you may experience an error like "/nix/store/.../lib/cups/filter/pstospl not available: No such file or directory".

Cause
When you create a printer profile you get a freeze version of cups filter and when cups is updated, because you have upgraded your system, and garbage collected this version is gone.

Solution
Go into the gnome-control-center printers settings, remove the printer and recreate it.