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.samsungUnifiedLinuxDriver — Proprietary Samsung Drivers
- pkgs.splix — Drivers for printers supporting SPL (Samsung Printer Language).
- Some printers might be supported by built-in CUPS drivers.
- Search for other printer drivers in the NixOS package directory.
(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.

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

Setting up shared printers

Server

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.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This article or section is out of date.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 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;
  services.avahi.nssmdns = true;
}

Alternately, the printer can be added to the client's CUPS daemon by navigating to http://localhost:631/ in a web browser and adding the remote printer.

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
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