Hi,
Is there any way to know how many users are present in Datatabase.?(eg. Any catalog tables,Like in oracle dba_users..?)

Version: 8.1.1.2.4
Fix pack level : 3

You can query the connections using the LIST APPLICATIONS command or by accessing the respective snapshot table functions.

In DB2, user ids are controlled at the OS level. However, the OS user id must be granted access to an object within DB2.

You could look at the syscat.dbauth and syscat.tableauth (and other views that end in AUTH) to see which users have been granted access to a DB2 resource. The complete list of catalog views in the SQL Reference Vol 1 Appendix D.

For sysadmin access that may have been granted, look in the dbm config.