Modifying user permissions within PostgreSQL can range from rather simple to extremely complex, depending on the permissive granularity that is actually required. In most cases, however, it is the powerful ALTER USER command that should be utilized to do everything from allowing users to login, create databases, manage roles, and even become a SUPERUSER account.

In this little HowTo, we will explore the power of the ALTER USER command so you can easily perform a variety of permission assignments and removals as the need arises.

Create a new user

Before we get into altering user permissions, we should establish a new user account (commonly referred to as a ROLE) to mess around with.

To begin, we’ll list all the existing users:

=# SELECT usename FROM pg_user;
 usename
----------
 postgres
(1 row)

By default, postgres is typically the only user that exists, so we want to create a new user of derpaderp to control our derpingdb database. This can be accomplished using the CREATE USER command:

=# CREATE USER derpaderp;
CREATE ROLE
=# SELECT usename FROM pg_user;
  usename
-----------
 postgres
 derpaderp
(2 rows)

Viewing existing user permissions

It can often be useful to examine the existing permissions assigned to the users in the system. This can easily be accomplished with the \du command from the psql prompt:

=# \du
                             List of roles
 Role name |                   Attributes                   | Member of
-----------+------------------------------------------------+-----------
 derpaderp |                                                | {}
 postgres  | Superuser, Create role, Create DB, Replication | {}

We can clearly see that even though we’ve now added a new derpaderp user, we have to assign it some permissions.

Altering existing user permissions

Now that our derpaderp user exists, we can begin using ALTER USER to modify the permissions granted to derpingdb.

The basic format of ALTER USER includes the name of the user (or ROLE) followed by a series of options to inform PostgreSQL which permissive alterations to make:

=# ALTER USER role_specification WITH OPTION1 OPTION2 OPTION3;

These options range from CREATEDB, CREATEROLE, CREATEUSER, and even SUPERUSER. Additionally, most options also have a negative counterpart, informing the system that you wish to deny the user that particular permission. These option names are the same as their assignment counterpart, but are prefixed with NO (e.g. NOCREATEDB, NOCREATEROLE, NOSUPERUSER).

Assigning SUPERUSER permission

Now that we understand the basics of creating users and using ALTER USER to modify permissions, we can quite simply use the SUPERUSER option to assign our derpaderp user SUPERUSER permission:

=# ALTER USER derpaderp WITH SUPERUSER;
ALTER ROLE

If we display our permission list now, we’ll see derpaderp has the new SUPERUSER permission we want:

=# \du
                             List of roles
 Role name |                   Attributes                   | Member of
-----------+------------------------------------------------+-----------
 derpaderp | Superuser                                      | {}
 postgres  | Superuser, Create role, Create DB, Replication | {}

Revoking permissions

In the event that we make a mistake and assign a permission we later wish to revoke, simply issue the same ALTER USER command but add the NO prefix in front of the permissive options to be revoked.

For example, we can remove SUPERUSER from our derpaderp user:

=# ALTER USER derpaderp WITH NOSUPERUSER;
ALTER ROLE
=# \du
                             List of roles
 Role name |                   Attributes                   | Member of
-----------+------------------------------------------------+-----------
 derpaderp |                                                | {}
 postgres  | Superuser, Create role, Create DB, Replication | {}

Questions/Comments?

Share:
What do you think of this post?
  • Sucks (0)
  • Boring (0)
  • Useful (0)
  • Interesting (0)
  • Awesome (0)
\