pg_dumpall is a utility for writing out ("dumping") all PostgreSQL databases of a cluster into one script file. The script file contains SQL commands that can be used as input to psql to restore the databases. It does this by calling pg_dump for each database in a cluster. pg_dumpall also dumps global objects that are common to all databases. (pg_dump does not save these objects.) This currently includes the information about database users and groups.
Thus, pg_dumpall is an integrated solution for backing up your databases. But note a limitation: it cannot dump "large objects", since pg_dump cannot dump such objects into text files. If you have databases containing large objects, they should be dumped using one of pg_dump's non-text output modes.
Since pg_dumpall reads tables from all databases you will most likely have to connect as a database superuser in order to produce a complete dump. Also you will need superuser privileges to execute the saved script in order to be allowed to add users and groups, and to create databases.
The SQL script will be written to the standard output. Shell operators should be used to redirect it into a file.
pg_dumpall accepts the following command line arguments:
Include SQL commands to clean (drop) database objects before recreating them. (This option is fairly useless, since the output script expects to create the databases themselves; they would always be empty upon creation.)
Only dump global objects (users and groups), no databases.
Specifies the host name of the machine on which the database server is running. If host begins with a slash, it is used as the directory for the Unix domain socket. The default is taken from the PGHOST environment variable, if set, else a Unix domain socket connection is attempted.
The port number on which the server is listening. Defaults to the PGPORT environment variable, if set, or a compiled-in default.
Connect as the given user.
Force a password prompt. This should happen automatically if the server requires password authentication.
Any other command line parameters are passed to the underlying pg_dump calls. This is useful to control some aspects of the output format, but some options such as -f, -t, and dbname should be avoided.
To dump all databases:
$ pg_dumpall > db.out
To reload this database use, for example:
$ psql -f db.out template1
(It is not important to which database you connect here since the script file created by pg_dumpall will contain the appropriate commands to create and connect to the saved databases.)