Then the script is trying to use root to populate the database and this will be difficult as the password for root is a randomly set 76 character password. Most install scripts have a place where you input the database information. Does the script allow you to input a username, password, etc?
If so, you need to input the fields something like this:
database type: MySQL
host: localhost
database: mwiki
username: mwikiuser
password: thepassword
If not, then you need to edit the script so that it uses "mwikiuser" as the user, "thepassword" as the password and "mwiki" as the database.