Cannot reset MySQL default root password after initial installation

I have installed mysql 5.7 on a Red Hat Enterprise Linux 5.5 server and when I tried to run following command after installation it is asking for a password for root@localhost. /usr/bin/mysql_secure_installation I have never set a root password and I'm logged in to Linux as root user. Then I have found following documentation for resetting root password and followed that one too. https://dev.mysql.com/doc/refman/5.5/en/resetting-permissions.html But even after starting the server with following command it is asking for a password /etc/init.d/mysqld start --skip-grant-tables & I have tried starting the server with init-file option, but no success. Does anyone know how to reset the password correctly or default MySQL password?