A must-read if you are planning to install DB2 on Solaris

db2ptree tool for Sun Solaris

From IBM FAQ:
Q :When installing DB2 on Solaris, my operating system level says SunOS 5.6. The DB2 for Solaris books say my operating system must be Solaris 2.6. Are these the same?

A: Yes, the operating system for Sun will display a SunOS version 5.x. This is the same as Solaris 2.x. For example, SunOS 5.8 is the same as Solaris 2.8.