Options for installing a Service Application: /username=name Sets the user account to run the service under. You must also ...

Options for installing a Service Application:
/username=name
    Sets the user account to run the service under. You must also
    specify the /password= option.

/password=pwd
    Sets the password for the account to run the service under.

The /username and /password options will be used only if the vendor of
the service designated it as requiring a user account. If a service was
so designated, and you do not use the /username and /password options,
you will be prompted at install time for the account.
/unattended
    Unattended install.  Will not prompt for username or password.