The first thing we want to do is create a simple textual dump:

[hs@linuxpc ~]$ pg_dump test > /tmp/dump.sql 

This is the most simplistic backup you can imagine. Basically, pg_dump logs in to the local database instance, connects to a database test, and starts to extract all of the data, which will then be sent to stdout and redirected to the file. The beauty here is that the standard output gives you all of the flexibility of a Unix system. You can easily compress the data using a pipe or do whatever you want to do with it.

In some cases, you might want to run pg_dump as a different user. All PostgreSQL client programs support a consistent set of command-line parameters to pass user information. If you just want to set the user, use the -U flag, as follows:

[hs@linuxpc ~]$ pg_dump -U whatever_powerful_user test > /tmp/dump.sql 

The following set of parameters can be found in all PostgreSQL client programs:

... 
Connection options: 
 -d, --dbname=DBNAME database to dump 
  -h, --host=HOSTNAME database server host or 
                           socket directory 
  -p, --port=PORT database server port number 
  -U, --username=NAME connect as specified database user 
  -w, --no-password never prompt for password 
  -W, --password force password prompt (should 
                           happen automatically) 
  --role=ROLENAME do SET ROLE before dump 
...

You can just pass the information you want to pg_dump, and if you have enough permissions, PostgreSQL will fetch the data. The important thing here is to see how the program really works. Basically, pg_dump connects to the database and opens a large repeatable read transaction that simply reads all of the data. Remember, a repeatable read ensures that PostgreSQL creates a consistent snapshot of the data, which does not change throughout the transactions. In other words, a dump is always consistent—no foreign keys will be violated. The output is a snapshot of data as it was when the dump started. Consistency is a key factor here. It also implies that changes made to the data while the dump is running won't make it to the backup anymore.

Also, note that the backup is in a textual format by default. This means that you can safely extract data from, say, Solaris, and move it to some other CPU architecture. In the case of binary copies, this is clearly not possible as the on-disk format depends on your CPU architecture.