Prior to Liferay Portal 6.1, the upgrade process required that "upgrade.process" property to be set in the portal-ext.properties.
For example, consider an upgrade from Liferay Portal 5.2 to Liferay Portal 6.0 SP2. Before Liferay Portal 6.1, the user would point the Portal 6.0 SP2 to the Liferay Portal 5.2 SP5 database. Then they would set their portal-ext.properties to include something like this:
upgrade.processes=\
com.liferay.portal.upgrade.UpgradeProcess_5_2_9_to_6_0_11,\
com.liferay.portal.upgrade.UpgradeProcess_6_0_12
Resolution
As long as Liferay Portal 6.2 is patched with the core-2 and upgrade-4 fix-packs or above, the property upgrade.processes is not required. Liferay automatically detects the original version and it will apply the required upgrade processes.