Hi Adil,
SUM can be used to apply both support pack stack as well as single patches.
For single patches you do not require stack xml file
What Ashish has mentioned is absolutely right. I would just like to add some important points to it.
1. Make sure the os user sidadm has proper permissions to that directory.
2. The full path to the directory does not exceed 25 characters otherwise SUM will give error as folllows
ERROR: Root directory /usr/sap/UPGRADE/SUM exceeds allowed length of 25, please use another one! (This was observed in UNIX system)
3. This directory should only contain those patches which are required. Avoid keeping any other files in this dir.
4. Make sure your database and SAP applications are up when starting SUM.
5. Take the latest SUM file and read the SAP note related to the SUM release.
6. Before extracting SUM to a directory confirm that you have sufficient space around 5 GB. SUM requires more space than JSPM.
Regards,
Robin Singh