My RHEL print server is sending SNMP queries to the printers. Why? Can I prevent this?

Environment

• Red Hat Enterprise Linux (RHEL) 5, 6, 7, and 8
• Common Unix Printing System (CUPS)

Issue

• SNMP queries are sent to printers when we print something by lpr like "lpr -P laserpr text.txt". Is the sending of SNMP queries when printing a implementation of CUPS? Can we disable this function?
• SNMP queries are causing delays in printing because the printer is taking several seconds to respond to the queries.

Resolution

To prevent CUPS from sending SNMP queries to printers, you can either:

• modify the PPD (PostScript Printer Definition) file for the print queue, or
• add an option to the Device URI for the queue.

To modify the PPD file, add the following line to the file for the appropriate print queue:

*cupsSNMPSupplies: False

To do this:

1. copy the PPD file from /etc/cups/ppd/<print-queue>.ppd to the /tmp directory, where <print-queue> is the name of the print queue for which you would like to disable SNMP queries. For example, if the print queue was named "laserpr" then the command would be:

    cp /etc/cups/ppd/laserpr.ppd /tmp/laserpr-mod.ppd
   

2. Use your favorite editor to add the following line to the PPD file near the top of the file before any "*OpenUI" statements:

    *cupsSNMPSupplies: False
   

   Save the file back to the PPD file in the /tmp directory.

3. Re-install the PPD file with an lpadmin command like the following:

    lpadmin -p laserpr -P /tmp/laserpr-mod.ppd
   

To add an option to the Device URI, add the "snmp=false" option to the end of the Device URI for the printer. To do this:

1. Retrieve the existing Device URI using the lpstat command. For example:

    $ lpstat -v laserpr
    device for laserpr: socket://10.1.2.3/
   

2. Run the lpadmin command with the -v option adding snmp=false to the end of the Device URI:

    lpadmin -p laserpr -v socket://10.1.2.3?snmp=false
   

   As with all URIs, the option is separated from the hostname (and optionally the port) with a question mark (?). If the Device URI already has an option, then the options are separated with ampersands (&). For example:

    $ lpstat -v laserpr
    device for laserpr: socket://10.1.2.3?waiteof=false
   

   then

    lpadmin -p laserpr -v 'socket://10.1.2.3?waiteof=false&snmp=false'
   

   If & is used, then the Device URI needs to be quoted to avoid special-character interpretation of & by the shell.

   The lpd:// backend should also accept the snmp=false option. For example:

    $ lpstat -v lpdprinter
    device for lpdprinter: lpd://10.1.2.3/lpdprinter
   
    $ lpadmin -p lpdprinter -v lpd://10.1.2.3/lpdprinter?snmp=false
   

Root Cause

Many of the CUPS "backend" programs send SNMP queries to the printers to get supply (ink, toner, paper, etc.) levels. The CUPS backend programs are the ones that communicate directly with the printers, and they reside in the /usr/lib/cups/backend directory. Currently, the ipp, lpd, and socket backend programs issue SNMP queries to retrieve supply information from the printer.

CUPS also sends SNMP broadcast queries to discover new printers. For more information about how CUPS does this and how to prevent it, please see the following Knowledgebase Solution:

Why is CUPS running on RHEL broadcasting SNMP requests? Can I stop it?

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