pgsql in a virtual environment

I am running a postgresql application under Mandriva 2011 x86_64, and
want to explore the problems in porting it to a Mageia 4 x86_64
environment before actually upgrading. I have installed Mageia 4 as a
virtual machine under VBox, installed postgresql 9.3 and sorted out a
shared folder to get to the existing database from which the application
needs to read data. However I cannot start the virtual postgresql with
the existing data directory:
$ ./pg_ctl start -D /mnt/post/pgsql/data &
[1] 3692
[postgres(at)localhost bin]$ pg_ctl: could not open PID file
"/mnt/post/pgsql/data/postmaster.pid": Protocol error

[1]+ Exit 1 ./pg_ctl start -D /mnt/post/pgsql/data
Is there any advice on running postgresql in a virtual machine
connecting to host data?
Thanks
Graeme