postgres@iama:~$ /usr/lib/postgresql/8.1/bin/postmaster -D /var/lib/postgresql/8.1/main_Rackable/     -c config_file=/var/lib/postgresql/8.1/main_Rackable/postgresql.conf
FATAL:  database files are incompatible with server
DETAIL:  The database cluster was initialized with PG_CONTROL_VERSION 738394112, but the server was compiled with PG_CONTROL_VERSION 812.
HINT:  It looks like you need to initdb.