Ensure that the domain is running.
Create the alias for the admin user. To do this, from the directory where the domain.xml file resides (install_dir/domains/domain_dir/config by default), run the following asadmin command:
create-password-alias --port 4848 --user admin --password adminadmin --aliaspassword adminadmin adminalias
Insert the alias in a passwordfile
$cat passwordfile
AS_ADMIN_PASSWORD=${ALIAS=adminalias}
Here's an example of the start-domain command used with the password alias.
asadmin start-domain --user admin --passwordfile passwordfile domain1