Change Password :
mysqladmin -u root -p'new123' password '123@root'

Backup and Restore All DB:
mysqldump --all-databases --single-transaction --user=root --password > all_databases.sql

Backup and Restore Single DB:
mysql -uroot -p < database_backup.sql
mysql -uroot -p database_name < mysql -uroot -p < database_backup.sql