Postgresql-Server won't start after moving data directory
Verify the permissions on /main with 

ls -l /media/daveknave/BIGFS/PGSQL/9.5/


Does postgres still have access to main? 

Switch user to postgres with su - postgres and then navigate through the directory structure /media/daveknave/BIGFS/PGSQL/9.5/main/. Can you navigate past main into base?

Verify the file permissions beneath ..../base with the following comamnds:

ls -lR /media/daveknave/BIGFS/PGSQL/9.5/main/base &gt; ~/postrgres_main_perm.log


and then 

vi ~/postrgres_main_perm.log


If you find that the permissions are not correct in the log file, then run the following command to grant postgres all permissions to the directory ...main/base and all underlying sub-directories:

chown -Rv postgres:postgres /media/daveknave/BIGFS/PGSQL/9.5/main/base/



  Caution:
  Before you modify all permissions ensure the command works by replacing chown -Rv with something less destructive like ls -R or navigate down to the .../main directory and issue the shorter command: chown -Rv postgres:postgres base/. This will ensure you are applying the command to the correct directory.


Try restarting your PostgreSQL instance again.