1) Run the DB2 command "-DISPLAY DATABASE(dbname)".
2) Take a look in SDSF to see whether the DB2 started task is up.
3) From within REXX, try the CONNECT statement of the DSNREXX interface.
check in spool that whether DB2 address space jobs running or not...search the spool with jobname starts with subsystem name.
You will find 4 or 5 address space jobs (MSTR,DBRC,SPAS,DIST each for one purpose). If they are not active you can say DB2 is down.