Step:
1. ubuntu 14.04
2. Postgresql9.3.7 > sudo apt-get install postgresql-9.3
3. install jdbc Driver > sudo apt-get install libpostgresql-jdbc-java
4. install Openkm 5.1.9
5. copy file postgresql-jdbc4-9.2.jar > cp /usr/share/java/postgresql-jdbc4-9.2.jar $JBOSS_HOME/server/default/lib/
6 follow this link http://wiki.openkm.com/index.php/PostgreSQL_-_OpenKM_5.0
note: don't forget to create database
