Just one correction to the above.
If I created domain with admin user as "administrator" and admin password as "mypassword" and if it is a developer profile domain masterpassword is "changeit" by default
asadmin start-domain --user administrator --passwordfile /password.txt
[Message sent by forum member 'sankarpn' (sankarpn)]
http://forums.java.net/jive/thread.jspa?messageID=301956