Introduction
In the last article, I introduced what CUPS (Common Unix Printing System) is and how, even in today's highly digital landscape, printing still plays a key role in supporting business processes. In this article, we’ll take the next step by exploring how to configure user access in CUPS through Role-Based Access Control (RBAC) to enhance security and control.
Understanding RBAC and Its Role in CUPS
RBAC, or Role-Based Access Control, is a method of managing user access by assigning permissions based on roles rather than individuals. In simple terms, it means restricting what a user—or group of users—can do based on what their job function requires or the level of access needed within a system, device, or application.
Why is this needed? Let’s explore that in the context of CUPS.
Table of Contents
- Introduction
- Understanding RBAC and Its Role in CUPS
- CUPS User Roles and Access Levels
- User Authentication in CUPS
- Locations and Policies in CUPS
CUPS User Roles and Access Levels
A good way to understand RBAC is through examples. Let’s break down CUPS user responsibilities into three distinct roles:
End Users: These could be cashiers, managers, or team leads in a warehouse. They either manually print documents or use applications that automatically send print jobs. Typically located near printers, their primary needs include verifying if a job was sent, checking on slow jobs, and reprinting if something goes wrong.
Help Desk: This is the first line of support when end users encounter issues they can’t solve. Help desk users may need to move jobs to another printer, cancel pending jobs, or perform most of the actions available to end users.
Admins: Admins provide second-level support and are responsible for maintaining and configuring CUPS across the enterprise. They handle tasks like adding or removing printers, analyzing logs, and resolving escalated issues. Admins can do everything help desk and end users can do, and more.
Under RBAC, each role receives an appropriate level of access. End users have the least privileges, while admins have the most. However, RBAC isn’t about status or hierarchy. Without end users, the help desk and admins have no one to support. Without admins, the help desk and users wouldn't have functioning systems. And, let’s face it—sometimes it’s better if some admins never directly interact with users.
User Authentication in CUPS
CUPS supports multiple authentication types: Basic, Digest, and Kerberos, depending on the version. Digest authentication may be deprecated in some versions, and Kerberos typically requires integration with Active Directory or similar centralized user authentication. For the purposes of this article, we’ll stick with Basic authentication.
With Basic authentication, CUPS uses the default Linux authentication system. Users are assigned to Linux groups, and those groups are then mapped to CUPS roles:
-
cups_viewer– End Users -
cups_help_desk– Help Desk -
cups_admin– Admins
To assign a user to the end user role, you would run the following command:
sudo usermod -aG cups_viewer <user id>
So, how does CUPS enforce these roles?
Locations and Policies in CUPS
CUPS uses Apache-style configuration syntax. Within the configuration files, two key directives help manage RBAC:
-
Location– defines where access is granted (relative to the CUPS web interface) -
Policy– defines what actions users can perform once access is granted
Location Tags
At first glance, you might assume Location refers to geographic or network location. However, in CUPS, it refers to URL paths on the web interface.
For example:
-
<Location />refers to the CUPS home page -
<Location /admin>refers to the administration page
To allow the cups_admin group to access the administration page, the following configuration can be used:
<Location /admin>
AuthType Basic
Require group cups_admin
Allow localhost
Allow 192.168.20.0/24
Allow 192.168.35.0/24
Order deny,allow
Encryption Required
</Location>
For a general login to the CUPS home page with basic user access, you can use a catch-all rule:
<Location />
Order allow,deny
Allow localhost
Allow 192.168.20.0/24
Allow 192.168.35.0/24
AuthType Basic
Require valid-user
Encryption Required
</Location>
So, Location defines where a user can go. But Policy defines what they can do once they get there.
Policy Tags and Action Limits
Policy blocks let you define named access rules. Inside these, you can use one or more Limit blocks to control access to specific CUPS actions.
Here’s an example policy for the help desk role:
<Policy help_desk>
<Limit Pause-Printer Resume-Printer Enable-Printer Disable-Printer Pause-Printer-After-Current-Job Hold-New-Jobs Release-Held-New-Jobs Deactivate-Printer Activate-Printer Restart-Printer Shutdown-Printer Startup-Printer Promote-Job Schedule-Job-After Cancel-Jobs CUPS-Accept-Jobs CUPS-Reject-Jobs Cancel-Job CUPS-Authenticate-Job>
AuthType Basic
Require group cups_help_desk
Encryption Required
Order deny,allow
</Limit>
</Policy>
In this configuration, users in the cups_help_desk group can access the /printers page because the root location / is set to allow any valid user, and there are no specific restrictions defined for the /printers path. Once there, they can perform administrative actions such as pausing or resuming printers, as permitted by the actions defined in the appropriate block.
Interestingly, different Limit blocks within the same Policy can be tied to different users or groups, giving you flexibility to finely control access.
When RBAC in CUPS Is Necessary
So, is RBAC truly needed for CUPS? It depends on your environment.
In a home setup, small business, or basic lab with just a few printers, all three roles (end user, help desk, admin) might be performed by the same individual. In such cases, RBAC may add unnecessary complexity.
However, in larger businesses—especially those with multiple locations and shared network printers—RBAC becomes essential. It not only protects printer queues from accidental or malicious misuse but also ensures users, help desk, and admins can work together efficiently to keep operations running smoothly.
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