How to share printers using Avahi and cups-browsed in CentOS 7.7

How to Fix

This method of printer sharing and discovery uses a set of service protocols (“multicast DNS” and “DNS Service Discovery”) that enables clients to discover shared printers on the master servers. The mDNS/DNS-SD protocols are implemented using Avahi and D-Bus in CentOS 7 and Rocky Linux 8. This method of printer sharing should be compatible with the Apple-branded “Bonjour” (sometimes called “Zeroconf”) system found in MacOS X.

For other methods of printer sharing and discovery using CUPS, please see the following Knowledgebase Solution:

How do I set up a master print server using CUPS in RHEL?

CUPS Master Print Server Configuration

1. Stop CUPS and back up your current CUPS configuration:

   # service cups stop
   # cp -a /etc/cups /etc/cups.saved
   

2. Edit /etc/cups/cupsd.conf to allow other servers to connect to printers on the master server. First change:

   Listen localhost:631
   

   to:

   Listen *:631
   

   or

   Listen 0.0.0.0:631
   

   This will configure CUPS to listen on all network interfaces. If you would like to limit CUPS to listening on a particular interface, enter the IP address of that interface instead of * or 0.0.0.0. For example:

   Listen 192.168.102.32:631
   

3. In cupsd.conf, add Allow @LOCAL to the bottom of the <Location /> stanza so It looks like the following:

   <Location />
     # Allow shared printing
     Order allow,deny
     Allow @LOCAL
   </Location>
   

   This will allow clients on the “local” network (the subnet on which the Master Print Server is located) to access CUPS on the Master Print Server. If you would like all clients to access the Master Print Server, then use “Allow all” instead of “Allow @Local“.

4. Install, enable, and start the D-Bus service. It’s probable that D-Bus is already installed and started. You can check this with the systemctl status command:

   # systemctl status dbus.service
   ● dbus.service - D-Bus System Message Bus
      Loaded: loaded (/usr/lib/systemd/system/dbus.service; static; vendor preset: disabled)
      Active: active (running) since Wed 2020-01-29 12:47:18 PST; 23h ago
   

   If the D-Bus service is not loaded and active, the following commands should install and start it:

   yum install dbus dbus-libs
   systemctl enable dbus.service
   systemctl restart dbus.service
   

5. Install, enable, and start Avahi service:

   yum install avahi
   systemctl enable avahi-daemon.service
   systemctl restart avahi-daemon.service
   

6. Stop and disable the “cups-browsed” service. It is not required as CUPS will communicate printer status to Avahi via D-Bus:

   systemctl stop cups-browsed
   systemctl disable cups-browsed
   

7. Start and enable CUPS:

   systemctl enable cups.service
   systemctl restart cups.service
   

   More information about CUPS printer browsing in CentOS 7 and later versions can be found in the following Knowledgebase Solution:

   CUPS Printer Browsing in CentOS 7

8. Make sure that each of your locally defined print queues is shared. The default is to share queues when they are created, so this shouldn’t be a problem. You can check the sharing status of a print queue by running the lpoptions command and looking for the printer-is-shared option as follows:

   # lpoptions -p textonly
   copies=1 device-uri=socket://10.3.4.5/ finishings=3 job-hold-until=no-hold job-priority=50 job-sheets=none,none
   marker-change-time=0 number-up=1 printer-commands=none printer-info=textonly printer-is-accepting-jobs=true
   printer-is-shared=true printer-location printer-make-and-model='Generic text-only printer' printer-state=3
   printer-state-change-time=1478741330 
   printer-state-reasons=none printer-type=4100
   printer-uri-supported=ipp://localhost:631/printers/textonly
   

   Note the entry printer-is-shared=true on the 3rd line in the output of the command above. You can also use the grep command to extract the value of printer-is-shared:

   # lpoptions -p textonly | egrep -o 'printer-is-shared=[^ ]+'
   printer-is-shared=true
   

   If the printer is not shared (i.e. the lpoptions command returns printer-is-shared=false), then the following command should share the printer:

   # lpatmin -p textonly -o printer-is-shared=true -E
   

9. Check to see that printers are defined and enabled on the master print server

   # lpstat -t
   scheduler is running
   no system default destination
   device for pcl: socket://10.1.2.3/
   device for postscript: socket://10.2.3.4/
   device for textonly: socket://10.3.4.5/
   pcl accepting requests since Wed 09 Nov 2016 05:28:19 PM PST
   postscript accepting requests since Wed 09 Nov 2016 05:28:37 PM PST
   textonly accepting requests since Wed 09 Nov 2016 05:28:50 PM PST
   printer pcl is idle.  enabled since Wed 09 Nov 2016 05:28:19 PM PST
   printer postscript is idle.  enabled since Wed 09 Nov 2016 05:28:37 PM PST
   printer textonly is idle.  enabled since Wed 09 Nov 2016 05:28:50 PM PST
   

10. If you have a firewall enabled on the master print server, reconfigure the firewall to allow outside access to port 631/ipp (as well as port 5353/mdns for CentOS 7) via UDP and TCP. Please refer to the appropriate RHEL Installation and Deployment Guides on how to do this for your particular version of RHEL.

CUPS Client Service Configuration

1. Install, enable, and start the D-Bus service. It’s probable that D-Bus is already installed and started. You can check this with the systemctl status command:

   # systemctl status dbus.service
   ● dbus.service - D-Bus System Message Bus
      Loaded: loaded (/usr/lib/systemd/system/dbus.service; static; vendor preset: disabled)
      Active: active (running) since Wed 2020-01-29 12:47:18 PST; 23h ago
   

   If the D-Bus service is not loaded and active, the following commands should install and start it:

   yum install dbus dbus-libs
   systemctl enable dbus.service
   systemctl restart dbus.service
   

2. Install, enable, and start the Avahi service:

   yum install avahi
   systemctl enable avahi-daemon.service
   systemctl start avahi-daemon.service
   

3. Install the NSS (Name Service Switch) mDNS (multicast DNS) plugin for glibc. This is required to resolve the .local names that Avahi uses:

   yum install nss-mdns
   

4. Make sure CUPS is started and enabled:

   systemctl enable cups.service
   systemctl start cups.service
   

Once the above steps are completed, the printers shared by the Master Print Server(s) should appear on the Client system:

# lpstat -t
scheduler is running
no system default destination
device for pcl: implicitclass:pcl
device for postscript: implicitclass:postscript
device for textonly: implicitclass: textonly
pcl accepting requests since Wed 09 Nov 2016 05:28:19 PM PST
postscript accepting requests since Wed 09 Nov 2016 05:28:37 PM PST
textonly accepting requests since Wed 09 Nov 2016 05:28:50 PM PST
printer pcl is idle.  enabled since Wed 09 Nov 2016 05:28:19 PM PST
printer postscript is idle.  enabled since Wed 09 Nov 2016 05:28:37 PM PST
printer textonly is idle.  enabled since Wed 09 Nov 2016 05:28:50 PM PST

The printers shared from the Master Print Server(s) use the implicitclass backend, as described in the following Knowledgebase Solution:

Running “lpstat -s” shows “implicitclass” in CentOS 7.7