PostgreSQL manages database access permissions using the concept of roles. A role can be thought of as either a database user, or a group of database users, depending on how the role is set up. Roles can own database objects (for example, tables and functions) and can assign privileges on those objects to other roles to control who has access to which objects. Furthermore, it is possible to grant membership in a role to another role, thus allowing the member role to use privileges assigned to another role.
The concept of roles subsumes the concepts of “users” and “groups”. In PostgreSQL versions before 8.1, users and groups were distinct kinds of entities, but now there are only roles. Any role can act as a user, a group, or both.
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:
For convenience, the programs createuser and dropuser are provided as wrappers around these SQL commands that can be called from the shell command line:
To determine the set of existing roles, examine the
pg_roles system catalog, for example
SELECT rolname FROM pg_roles;
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 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, 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
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. (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.
A database role can have a number of attributes that define its privileges and interact with the client authentication system.
Only roles that have the
LOGIN attribute can be used as the initial role name for a database connection. A role with the
LOGIN attribute can be considered the same as a “database user”. To create a role with login privilege, use either:
CREATE USER is equivalent to
CREATE ROLE except that
CREATE USER includes
LOGIN by default, while
CREATE ROLE does not.)
A database superuser bypasses all permission checks, except the right to log in. This is a dangerous privilege and should not be used carelessly; it is best to do most of your work as a role that is not a superuser. To create a new database superuser, use
CREATE ROLE name SUPERUSER. You must do this as a role that is already a superuser.
A role must be explicitly given permission to create databases (except for superusers, since those bypass all permission checks). To create such a role, use
CREATE ROLE name CREATEDB.
A role must be explicitly given permission to create more roles (except for superusers, since those bypass all permission checks). To create such a role, use
CREATE ROLE name CREATEROLE. A role with
CREATEROLE privilege can alter and drop other roles, too, as well as grant or revoke membership in them. However, to create, alter, drop, or change membership of a superuser role, superuser status is required;
CREATEROLE is insufficient for that.
A role must explicitly be given permission to initiate streaming replication (except for superusers, since those bypass all permission checks). A role used for streaming replication must have
LOGIN permission as well. To create such a role, use
CREATE ROLE name REPLICATION LOGIN.
A password is only significant if the client authentication method requires the user to supply a password when connecting to the database. The
md5 authentication methods make use of passwords. Database passwords are separate from operating system passwords. Specify a password upon role creation with
CREATE ROLE name PASSWORD 'string'.
A role’s attributes can be modified after creation with
ALTER ROLE. See the reference pages for the CREATE ROLE and ALTER ROLE commands for details.
A role can also have role-specific defaults for many of the run-time configuration settings. For example, if for some reason you want to disable index scans (hint: not a good idea) anytime you connect, you can use:
ALTER ROLE myname SET enable_indexscan TO off;
This will save the setting (but not set it immediately). In subsequent connections by this role it will appear as though
SET enable_indexscan TO off had been executed just before the session started. You can still alter this setting during the session; it will only be the default. To remove a role-specific default setting, use
ALTER ROLE rolename RESET varname. Note that role-specific defaults attached to roles without
LOGIN privilege are fairly useless, since they will never be invoked.
It is frequently convenient to group users together to ease management of privileges: that way, privileges can be granted to, or revoked from, a group as a whole. In PostgreSQL this is done by creating a role that represents the group, and then granting membership in the group role to individual user roles.
To set up a group role, first create the role:
Typically a role being used as a group would not have the
LOGIN attribute, though you can set it if you wish.
Once the group role exists, you can add and remove members using the GRANT and REVOKE commands:
role1, ... ;
role1, ... ;
You can grant membership to other group roles, too (since there isn’t really any distinction between group roles and non-group roles). The database will not let you set up circular membership loops. Also, it is not permitted to grant membership in a role to
The members of a group role can use the privileges of the role in two ways. First, every member of a group can explicitly do SET ROLE to temporarily “become” the group role. In this state, the database session has access to the privileges of the group role rather than the original login role, and any database objects created are considered owned by the group role not the login role. Second, member roles that have the
INHERIT attribute automatically have use of the privileges of roles of which they are members, including any privileges inherited by those roles. As an example, suppose we have done:
CREATE ROLE joe LOGIN INHERIT;
CREATE ROLE admin NOINHERIT;
CREATE ROLE wheel NOINHERIT;
GRANT admin TO joe;
GRANT wheel TO admin;
Immediately after connecting as role
joe, a database session will have use of privileges granted directly to
joe plus any privileges granted to
admin‘s privileges. However, privileges granted to
wheel are not available, because even though
joe is indirectly a member of
wheel, the membership is via
admin which has the
NOINHERIT attribute. After:
SET ROLE admin;
the session would have use of only those privileges granted to
admin, and not those granted to
SET ROLE wheel;
the session would have use of only those privileges granted to
wheel, and not those granted to either
admin. The original privilege state can be restored with any of:
SET ROLE joe;
SET ROLE NONE;
The role attributes
CREATEROLE can be thought of as special privileges, but they are never inherited as ordinary privileges on database objects are. You must actually
SET ROLE to a specific role having one of these attributes in order to make use of the attribute. Continuing the above example, we might choose to grant
CREATEROLE to the
admin role. Then a session connecting as role
joe would not have these privileges immediately, only after doing
SET ROLE admin.
To destroy a group role, use DROP ROLE:
Any memberships in the group role are automatically revoked (but the member roles are not otherwise affected).
Because roles can own database objects and can hold privileges to access other objects, dropping a role is often not just a matter of a quick DROP ROLE. Any objects owned by the role must first be dropped or reassigned to other owners; and any permissions granted to the role must be revoked.
Ownership of objects can be transferred one at a time using
ALTER commands, for example:
ALTER TABLE bobs_table OWNER TO alice;
Alternatively, the REASSIGN OWNED command can be used to reassign ownership of all objects owned by the role-to-be-dropped to a single other role. Because
REASSIGN OWNED cannot access objects in other databases, it is necessary to run it in each database that contains objects owned by the role. (Note that the first such
REASSIGN OWNED will change the ownership of any shared-across-databases objects, that is databases or tablespaces, that are owned by the role-to-be-dropped.)
Once any valuable objects have been transferred to new owners, any remaining objects owned by the role-to-be-dropped can be dropped with the DROP OWNED command. Again, this command cannot access objects in other databases, so it is necessary to run it in each database that contains objects owned by the role. Also,
DROP OWNED will not drop entire databases or tablespaces, so it is necessary to do that manually if the role owns any databases or tablespaces that have not been transferred to new owners.
DROP OWNED also takes care of removing any privileges granted to the target role for objects that do not belong to it. Because
REASSIGN OWNED does not touch such objects, it’s typically necessary to run both
REASSIGN OWNED and
DROP OWNED (in that order!) to fully remove the dependencies of a role to be dropped.
In short then, the most general recipe for removing a role that has been used to own objects is:
REASSIGN OWNED BY doomed_role TO successor_role;
DROP OWNED BY doomed_role;
-- repeat the above commands in each database of the cluster
DROP ROLE doomed_role;
When not all owned objects are to be transferred to the same successor owner, it’s best to handle the exceptions manually and then perform the above steps to mop up.
DROP ROLE is attempted while dependent objects still remain, it will issue messages identifying which objects need to be reassigned or dropped.
PostgreSQL provides a set of default roles which provide access to certain, commonly needed, privileged capabilities and information. Administrators can GRANT these roles to users and/or other roles in their environment, providing those users with access to the specified capabilities and information.
The default roles are described in Table below. Note that the specific permissions for each of the default roles may change in the future as additional capabilities are added. Administrators should monitor the release notes for changes.
|pg_read_all_settings||Read all configuration variables, even those normally visible only to superusers.|
|pg_read_all_stats||Read all pg_stat_* views and use various statistics related extensions, even those normally visible only to superusers.|
|pg_stat_scan_tables||Execute monitoring functions that may take |
|pg_monitor||Read/execute various monitoring views and functions. This role is a member of |
|pg_signal_backend||Signal another backend to cancel a query or terminate its session.|
|pg_read_server_files||Allow reading files from any location the database can access on the server with COPY and other file-access functions.|
|pg_write_server_files||Allow writing to files in any location the database can access on the server with COPY and other file-access functions.|
|pg_execute_server_program||Allow executing programs on the database server as the user the database runs as with COPY and other functions which allow executing a server-side program.|
pg_stat_scan_tables roles are intended to allow administrators to easily configure a role for the purpose of monitoring the database server. They grant a set of common privileges allowing the role to read various useful configuration settings, statistics and other system information normally restricted to superusers.
pg_signal_backend role is intended to allow administrators to enable trusted, but non-superuser, roles to send signals to other backends. Currently this role enables sending of signals for canceling a query on another backend or terminating its session. A user granted this role cannot however send signals to a backend owned by a superuser.
pg_execute_server_program roles are intended to allow administrators to have trusted, but non-superuser, roles which are able to access files and run programs on the database server as the user the database runs as. As these roles are able to access any file on the server file system, they bypass all database-level permission checks when accessing files directly and they could be used to gain superuser-level access, therefore great care should be taken when granting these roles to users.
Care should be taken when granting these roles to ensure they are only used where needed and with the understanding that these roles grant access to privileged information.
Administrators can grant access to these roles to users using the GRANT command, for example:
GRANT pg_signal_backend TO admin_user;
Functions, triggers and row-level security policies allow users to insert code into the backend server that other users might execute unintentionally. Hence, these mechanisms permit users to “Trojan horse” others with relative ease. The strongest protection is tight control over who can define objects. Where that is infeasible, write queries referring only to objects having trusted owners. Remove from
search_path the public schema and any other schemas that permit untrusted users to create objects.
Functions run inside the backend server process with the operating system permissions of the database server daemon. If the programming language used for the function allows unchecked memory accesses, it is possible to change the server’s internal data structures. Hence, among many other things, such functions can circumvent any system access controls. Function languages that allow such access are considered “untrusted”, and PostgreSQL allows only superusers to create functions written in those languages.