The pbsnodes utility: change node status

 List all the nodes:
#pbsnodes -a  

Take one node offline:
#pbsnodes -o node_name

Clear the offline bit:
#pbsnodes -c node_name

pbsnodes command options:
-a             All attributes of a node or all nodes are listed.   This
                      is the default if no flag is given.
 
-o             Add the OFFLINE state.  This  is  different  from  being
                      marked  DOWN.  OFFLINE prevents new jobs from running on
                      the specified nodes.  This  gives  the  administrator  a
                      tool to hold a node out of service without changing any-
                      thing else.  The OFFLINE state  will  never  be  set  or
                      cleared  automatically  by  pbs_server; it is purely for
                      the manager or operator.

-c             Clear OFFLINE from listed nodes