Error_startup postgresql server

Hi,

I'm using Postgresql 8.7.3 on Debian. I was trying to launch the postgresql
server to create a simple user and a database, but I've got this output:

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jc:/usr/local/pgsql/data1# su - postgres
postgres(at)jc:~$ /usr/local/pgsql/bin/pg_ctl start -l logfile -D
/usr/local/pgsql/data1/data/
server starting
postgres(at)jc:~$ /usr/local/pgsql/bin/createuser radius --no-superuser
--no-createdb --no-createrole -P
Enter password for new role:
Enter it again:
createuser: could not connect to database postgres: could not connect to
server: No such file or directory
Is the server running locally and accepting
connections on Unix domain socket "/tmp/.s.PGSQL.5432"?
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I've search the web and seen some people saying to uncomment a line in the
postgresql.conf file ("tcpip_socket = true") but I don't have this line! I'm
not understanding what's wrong, why can't I create an user, supposedly the
server is running..

Can someone tell me what am I doing wrong?

Thank you,
Joana Camacho.