As we know mysqldump is used for taking back up of database, Lets see your command :
you have executed mysqldump -u admin -p password productdb
Now Lets see the correct syntax :
mysqldump -u <user_name> -p<user_password>
We have found what you are missing here see you have an space between -p and your password while according to correct syntax their should not be space between them.
I hope you got my point.