I am new to OpenKM and would like to know if I can install on UBUNTU desktop and use it as server...or do i need to download UBUNTU server (without UI) and install on it ..please guide whats the better option.
For test environment you can use any OS version but if you plan install on production environment I suggest use Ubuntu Server 14.04 LTS 64 bits version. In this case probably the best download will be the tomcat-bundle ( not the installer ).
Take a look here http://wiki.openkm.com/index.php/Quick_ ... OpenKM_6.2 and http://wiki.openkm.com/index.php/Installation_Guide