When you want to delete a fax job in queue, you will receive “504 cannot kill job operation not permitted”
Even if you try to remove faxes as root, system will not give you permission.
To solve this, first see the job numbers using this command
After that remove the fax jobs using this command :
faxrm -v -u nobody <JOBID>
Please note: nobody is the owner of fax job. You get this information on previous command.