pbs_mom is the PBS Execution service that runs on a compute node and is started if PBS_START_MOM=1 in the /etc/pbs.conf.
You can get more information by looking at the man pages for pbs_mom ( e.g., man pbs_mom ).
Some basic commands are qstat, qmgr , qsub , qdel etc ( man qsub , man qstat for help pages).
You can also browse the PBS Pro documentation at this page Altair Product Documentation - Altair Community
To check whether PBS Services are running:
ps -ef | grep pbs_
/etc/init.d/pbs status
systemctl status pbs
Note:
Depends on the services that are enabled in /etc/pbs.conf
e.g., where all services are enabled/started
PBS_START_SERVER=1
PBS_START_SCHED=1
PBS_START_COMM=1
PBS_START_MOM=1