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Could you please browse this document: https://resources.altair.com/resfile_web_path/file-en/PBSWorks_Whitepaper_PBSProfessional_VirtualTestCluster_Ubuntu_02202020.pdf 
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In your setup what is the output of 
      hostname
      hostname -A  , hostname -i  
      source /etc/pbs.conf
      pbs_hostn -v  $PBS_SERVER
      ping  $PBS_SERVER