CentOS 6.0 mysql upgrade 5.1 to 5.7 and mysqld start error

http://www.tecmint.com/install-latest-mysql-on-rhel-centos-and-fedora/

http://redeyesofangel.tistory.com/861

when service mysqld start failed,

sudo mysqld_safe --skip-grant-tables

sudo mysql_upgrade -u root -p