Postgresql – How to find PostgreSQL’s data directory

If you are doing a minor version upgrade, nothing will or should touch your data directory. If you are using binary packages, just run whatever upgrade procedure they provide (apt/yum upgrade, etc.). If building from source, just do make install over the old files and then restart the server (pg_ctl restart or whatever you're using).

The documentation could perhaps be amended to say that you could even install the new binaries before restarting the server.

There error is telling ... The problem is that you ran initdb as your local login, but I'm pretty that your login (username) doesn't have access to /var/run/postgresql. If you have a clean install, may I recommend that you remove the data directory and start all over, this time by su-ing into the postgres account:

username@jupiter:~$ sudo su - postgres

Then you can initdb

postgres@jupiter:~$ /usr/lib/postgresql/8.4/bin/initdb --encoding=UTF8 --pgdata=/mydata/pgdbdata/

Also, as Catcall mentioned, make sure you're using the correct location for your data.