108.4 Lesson 1

Most Linux desktop installations will have the CUPS packages already installed. On minimal Linux installations the CUPS packages may not be installed, depending on the distribution. A basic CUPS installation can be performed on a Debian system with the following:

On Fedora systems the installation process is just as easy. You will need to start the CUPS service manually after installation on Fedora and other Red Hat-based distributions:

After the installation has completed, you can verify that the CUPS service is running with the use of the systemctl command:

As with many other Linux daemons, CUPS relies on a set of configuration files for its operations. Listed below are the main ones that are of interest to the system administrator:

The CUPS service also utilizes logging in much the same manner as the Apache 2 service. The logs are stored within /var/log/cups/ and contain an access_log, page_log, and an error_log. The access_log keeps a record of access to the CUPS web interface as well as actions taken within it, such as printer management. The page_log keeps track of print jobs that have been submitted to the print queues managed by the CUPS installation. The error_log will contain messages about print jobs that have failed and other errors recorded by the web interface.

We will next look at the tools and utilities that are used to manage the CUPS service.

Adding a printer queue to the system is a simple process within the CUPS web interface:

A printer’s queue may also be installed using the legacy LPD/LPR commands. Here is an example using the lpadmin command:

We will break down the command to illustrate the options used here:

As stated previously, it is best to let CUPS automatically determine which PPD file to use for a particular print queue. However, the legacy lpinfo command can be used to query the locally installed PPD files to see what are available. Just provide the --make-and-model option for the printer you wish to install and the -m option:

Note that the lpinfo command is deprecated. It is shown here as an example of listing out what print driver files a printer could use.

A default printer can be set using the lpoptions command. This way, should the majority (or all) print jobs be sent to a particular printer then the one specified with the lpoptions command will be the default. Just specify the printer along with the -d option:

Once a printer has been installed an administrator could use the web interface to manage the options that are available to the printer. A more direct approach to managing a printer is through the use of the lpadmin command.

One option is allowing the ability for a printer to be shared on the network. This can be achieved with the printer-is-shared option, and by specifying the printer with the -p option:

An administrator can also configure a print queue to only accept print jobs from specific users with each user separated by a comma:

Inversely, only specific users could be denied access to a specific print queue:

User groups could also be used to allow or deny access to a printer’s queue provided that the group’s name is preceded by an “at” (@) character:

A print queue can also have an error policy should it encounter issues printing a job. With the use of policies, a print job could be aborted (abort-job) or another attempt to print it could occur at a later time (retry-job). Other policies include the ability to stop the printer immediately should an error occur (stop-printer) as well as the ability to retry the job immediately after a failure is detected (retry-current-job). Here is an example where the printer policy is set to abort the print job should an error occur on the FRONT-DESK printer:

Be sure to review the manual pages for the lpadmin command located at lpadmin(8) for further details on the usage of this command.

Many desktop applications will allow you to submit print jobs from a menu item or by using the Ctrl+p keyboard shortcut. Should you find yourself on a Linux system that does not utilize a desktop environment, you can still send files to a printer by way of the legacy LPD/LPR commands.

The lpr (“line printer remote”) command is used to send a print job to a printer’s queue. In the command’s most basic form, a file name along with the lpr command is all that is required:

The above command will send the file report.txt to the default print queue for the system (as identified by the /etc/cups/printers.conf file).

If a CUPS installation has multiple printers installed then the lpstat command can be used to print out a list of available printers using the -p option and the -d option will indicate which is the default printer:

So in our example here, the report.txt file will be sent to the ENVY-4510 printer as it is set as the default. Should the file need to be printed at a different printer, specify the printer along with the -P option:

When a print job is submitted to CUPS the daemon will figure out which backend is best suited to handle the task. CUPS can make use of various printer drivers, filters, hardware port monitors and other software to properly render the document. There will be times when a user printing a document will need to make modifications to how the document should be printed. Many graphical applications make this task rather easy. There are also command line options that can be utilized to change how a document should be printed. When a print job is submitted via the command line, the -o switch (for “options”) can be used in conjunction with specific terms to adjust the document’s layout for printing. Here is a short list of commonly used options:

Taking a sampling of the options above, the following example command can be constructed:

More than one copy of a document can be printed by using the number option in the following format: -#N where N is equal to the number of copies to print. Here is an example with the collate option where seven copies of a report are to be printed on the default printer:

Aside from the lpr command, the lp command can also be used. Many of the options that are used with the lpr command can also be used with the lp command, but there are some differences. Be sure to consult the man page at lp(1) for reference. Here is how we can run the previous example lpr command using the syntax of the lp command while also specifying the destination printer with the -d option:

As stated earlier, each print job submitted to the print queue receives a job ID from CUPS. A user can view the print jobs that they have submitted with the lpq command. Passing in the -a option will show the queues of all printers that are managed by the CUPS installation:

The same lpstat command used previously also has an option to view printer queues. The -o option by itself will show all print queues, or a print queue can be specified by name:

The print job ID will be prepended with the name of the queue where the job was sent, then the name of the user that submitted the job, the file’s size, and the time it was submitted.

Should a print job get stuck on a printer or a user wishes to cancel their print job, use the lprm command along with the job ID found from the lpq command:

All jobs in a print queue could be deleted at once by providing just a dash -:

Alternatively, the CUPS cancel command could also be used by a user to stop their current print job:

A specific print job can be cancelled by its job ID prepended by the printer name:

A print job can also be moved from one print queue to another. This is often helpful should a printer stop responding or the document to be printed requires features available on a different printer. Take note that this procedure typically requires a user with elevated privileges. Using the same print job from the previous example, we could move it to the queue of the FRONT-DESK printer:

To remove a printer, it is often helpful to first list out all of the printers that are currently managed by the CUPS service. This can be done with the lpstat command:

The -v option not only lists out the printers but also where (and how) they are attached. It is good practice to first reject any new jobs going to the printer and provide a reason as to why the printer will not be accepting new jobs. This can be done with the following:

Note the use of sudo as this task requires a user with elevated privileges.

To remove a printer, we utilize the lpadmin command with the -x option to delete the printer: