pg_ctl start check sum failed

Hello,

I   try to use an old cluster into a new system.

The new system comes with a newer version of postgres so I uninstalled it  and I installed the same version that I had in the older system --->8.1

I got impressed when I Installed the 8.1 with dpkg -i and it started to run without starting the daemon...

Is it possible to know  what directory is the server using to store the data?

--- main question

Once I have installed the server I try to start it using pg_control start -D /oldCluster directory but I get FATAL checksum incorrect.

I want to use the old data, any ideas?

Many thanks