21.1. Database Roles
Database roles are conceptually completely separate from operating system users. In practice it might be convenient to maintain a correspondence, but this is not required. Database roles are global across a database cluster installation (and not per individual database). To create a role use the CREATE ROLE SQL command:
name follows the rules for SQL
identifiers: either unadorned without special characters, or
double-quoted. (In practice, you will usually want to add additional
options, such as
LOGIN, to the command. More details appear
below.) To remove an existing role, use the analogous
DROP ROLE command:
To determine the set of existing roles, examine the
system catalog, for example
SELECT rolname FROM pg_roles;
The psql program's
is also useful for listing the existing roles.
In order to bootstrap the database system, a freshly initialized
system always contains one predefined role. This role is always
a “superuser”, and by default (unless altered when running
initdb) it will have the same name as the
operating system user that initialized the database
cluster. Customarily, this role will be named
postgres. In order to create more roles you
first have to connect as this initial role.
Every connection to the database server is made using the name of some
particular role, and this role determines the initial access privileges for
commands issued in that connection.
The role name to use for a particular database
connection is indicated by the client that is initiating the
connection request in an application-specific fashion. For example,
psql program uses the
-U command line option to indicate the role to
connect as. Many applications assume the name of the current
operating system user by default (including
psql). Therefore it
is often convenient to maintain a naming correspondence between
roles and operating system users.
The set of database roles a given client connection can connect as is determined by the client authentication setup, as explained in Chapter 20. (Thus, a client is not limited to connect as the role matching its operating system user, just as a person's login name need not match his or her real name.) Since the role identity determines the set of privileges available to a connected client, it is important to carefully configure privileges when setting up a multiuser environment.