postgres
su postgres .. to get into his shell account
psql .. to login to sql
Navigate the database:
\list .... list the databases
\c [DB] .... to select the database [DATABASE]
\d .... to list the tables
select * from users;
File Traverse
You can read a file from psql, that you normally wouldnt be allowed!
CREATE TABLE demo(t text);
COPY demo from '[/var/lib/postgresql/9.4/key.txt]';
SELECT * FROM demo;