(cups-print-server)=
# Install and configure a CUPS print server

The [Common UNIX Printing System, or CUPS](https://openprinting.github.io/cups/doc/overview.html), is the most widely-used way to manage printing and print services in Ubuntu. This freely-available printing system has become the standard for printing in most Linux distributions, and uses the standard Internet Printing Protocol (IPP) to handle network printing.

CUPS manages print jobs and queues, and provides support for a wide range of printers, from dot-matrix to laser, and many in between. CUPS also supports PostScript Printer Description (PPD) and auto-detection of network printers, and features a simple web-based configuration and administration tool.

## Install CUPS

A complete CUPS install has many package dependencies, but they can all be specified on the same command line. To perform a basic installation of CUPS, enter the following command in your terminal:

```bash
sudo apt install cups
```

Once the download and installation have finished, the CUPS server will be started automatically.

## Configure the CUPS server

The CUPS server's behavior is configured through directives found in the `/etc/cups/cupsd.conf` configuration file. This CUPS configuration file follows the same syntax as the main configuration file for the Apache HTTP server. Some examples of commonly-configured settings will be presented here.

### Make a copy of the configuration file

We recommend that you make a copy of the original CUPS configuration file and protect it from writing, before you start configuring CUPS. You will then have the original settings as a reference, which you can reuse or restore as necessary.

```bash
sudo cp /etc/cups/cupsd.conf /etc/cups/cupsd.conf.original
sudo chmod a-w /etc/cups/cupsd.conf.original
```

### Configure Server administrator

To configure the email address of the designated CUPS server administrator, edit the `/etc/cups/cupsd.conf` configuration file with your preferred text editor, and add or modify the **ServerAdmin** line accordingly. For example, if you are the administrator for the CUPS server, and your e-mail address is `bjoy@somebigco.com`, then you would modify the ServerAdmin line to appear as follows:

```text
ServerAdmin bjoy@somebigco.com
```

### Configure Listen

By default on Ubuntu, CUPS listens only on the loopback interface at IP address `127.0.0.1`.

To instruct CUPS to listen on an actual network adapter's IP address, you must specify either a hostname, the IP address, or (optionally) an IP address/port pairing via the addition of a **Listen** directive.

For example, if your CUPS server resides on a local network at the IP address `192.168.10.250` and you'd like to make it accessible to the other systems on this subnetwork, you would edit the `/etc/cups/cupsd.conf` and add a Listen directive, as follows:

```text
Listen 127.0.0.1:631           # existing loopback Listen
Listen /var/run/cups/cups.sock # existing socket Listen
Listen 192.168.10.250:631      # Listen on the LAN interface, Port 631 (IPP)
```

In the example above, you can comment out or remove the reference to the Loopback address (`127.0.0.1`) if you do not want the CUPS daemon (`cupsd`) to listen on that interface, but would rather have it only listen on the Ethernet interfaces of the Local Area Network (LAN). To enable listening for all network interfaces for which a certain hostname is bound, including the Loopback, you could create a Listen entry for the hostname `socrates` like this:

```text    
Listen socrates:631  # Listen on all interfaces for the hostname 'socrates'
```

or by omitting the Listen directive and using **Port** instead, as in:

```text
Port 631  # Listen on port 631 on all interfaces
```

For more examples of configuration directives in the CUPS server configuration file, view the associated system manual page by entering the following command:

```bash
man cupsd.conf
```

## Post-configuration restart

Whenever you make changes to the `/etc/cups/cupsd.conf` configuration file, you'll need to restart the CUPS server by typing the following command at a terminal prompt:

```bash
sudo systemctl restart cups.service
```

## Web Interface

CUPS can be configured and monitored using a web interface, which by default is available at `http://localhost:631/admin`. The web interface can be used to perform all printer management tasks.

To perform administrative tasks via the web interface, you must either have the root account enabled on your server, or authenticate as a user in the `lpadmin` group. For security reasons, CUPS won't authenticate a user that doesn't have a password.

To add a user to the `lpadmin` group, run at the terminal prompt:

```bash
sudo usermod -aG lpadmin username
```

Further documentation is available in the "Documentation/Help" tab of the web interface.

## Error logs

For troubleshooting purposes, you can access CUPS server errors via the error log file at: `/var/log/cups/error_log`. If the error log does not show enough information to troubleshoot any problems you encounter, the verbosity of the CUPS log can be increased by changing the **LogLevel** directive in the configuration file (discussed above) from the default of "info" to "debug" or even "debug2", which logs everything.

If you make this change, remember to change it back once you've solved your problem, to prevent the log file from becoming overly large.

## References

* [CUPS Website](http://www.cups.org/)

* [Debian Open-iSCSI page](http://wiki.debian.org/SAN/iSCSI/open-iscsi)