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:
CREATE ROLE name
;
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:
DROP ROLE name
;
For convenience, the programs createuser and dropuser are provided as wrappers around these SQL commands that can be called from the shell command line:
createusername
dropusername
To determine the set of existing roles, examine the pg_roles
system catalog, for example:
SELECT rolname FROM pg_roles;
or to see just those capable of logging in:
SELECT rolname FROM pg_roles WHERE rolcanlogin;
The psql program's \du
meta-command
is also useful for listing the existing roles.
In order to bootstrap the database system, a freshly initialized
system always contains one predefined login-capable role. This role
is always a “superuser”, and it will have
the same name as the operating system user that initialized the
database cluster with initdb
unless a different name
is specified. This role is often 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,
the 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
createuser
and 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.