Kill a postgresql session/connection

How can I kill all my postgresql connections?

I'm trying a rake db:drop but I get:

ERROR:  database "database_name" is being accessed by other users
DETAIL:  There are 1 other session(s) using the database.

I've tried shutting down the processes I see from a ps -ef | grep postgres but this doesn't work either:

kill: kill 2358 failed: operation not permitted

You can use pg_terminate_backend() to kill a connection. You have to be superuser to use this function. This works on all operating systems the same.

SELECT 
    pg_terminate_backend(pid) 
FROM 
    pg_stat_activity 
WHERE 
    -- don't kill my own connection!
    pid <> pg_backend_pid()
    -- don't kill the connections to other databases
    AND datname = 'database_name'
    ;

Before executing this query, you have to REVOKE the CONNECT privileges to avoid new connections:

REVOKE CONNECT ON DATABASE dbname FROM PUBLIC, username;

If you're using Postgres 8.4-9.1 use procpid instead of pid

SELECT 
    pg_terminate_backend(procpid) 
FROM 
    pg_stat_activity 
WHERE 
    -- don't kill my own connection!
    procpid <> pg_backend_pid()
    -- don't kill the connections to other databases
    AND datname = 'database_name'
    ;