iiab/roles/cups

CUPS Printing README

CUPS (also known as the "Common UNIX Printing System") is the standards-based, open source printing system for Linux and macOS.

It allows your Internet-in-a-Box (IIAB) to act as a print server.

This can be useful if a printer is attached to your IIAB — so student/teacher print jobs from client computers and phones can be processed — and then sent to the appropriate printer.

Using it

Make sure your IIAB was installed with these 2 lines in /etc/iiab/local_vars.yml :

cups_install: True
cups_enabled: True

Then visit your IIAB's http://box/print > Administration and log in using:

• Username: Admin
• Password: changeme

Or use any Linux account that is a member of the Linux group: lpadmin

Browser pop-ups will try to scare you — click (and persist!) to log in despite these exaggerated warnings.

Security

The above uses 'SystemGroup lpadmin' in /etc/cups/cups-files.conf — in coordination with about 15 '@SYSTEM' lines and 'DefaultAuthType Basic' in /etc/cups/cupsd.conf

CUPS creates a 10-year "self-signed" HTTPS certificate during installation, that will be very confusing to non-technical users when they log in, as a result of modern browser warnings.

How it Works

Understand how IIAB configures CUPS for all IP addresses and all hostnames (IIAB redirects to bypass the "since 2009" CUPS problem mentioned below!) by reading these in-line explanations:

• /opt/iiab/iiab/roles/cups/tasks/install.yml

Modify these 2 files at your own risk:

• /etc/cups/cupsd.conf (run sudo cupsctl and sudo cupsd -t to verify the file!)
• /etc/nginx/conf.d/cups.conf

If you make modifications to the above files, don't forget to restart systemd services: (run this as root)

systemctl restart cups cups-browsed nginx

Troubleshooting

Visit your IIAB's http://box/print > Help for printer configuration suggestions, Etc!

http://localhost:631 is very useful if NGINX redirects or CUPS permissions are set wrong.

Beware that http://box:631 and http://box.lan:631 will not work, due to a known issue with CUPS since 2009.

Run ps aux | grep cups and systemctl status cups to verify the CUPS systemd service is running well.

Finally, keep an eye on: /var/log/cups/error_log

Docs and Updates

• https://www.cups.org/documentation.html
  • https://github.com/apple/cups/releases
• https://openprinting.github.io/cups/
  • https://github.com/OpenPrinting/cups/releases/