https://stackoverflow.com/questions/33510184/change-mysql-root-password-on-centos7/34207996#34207996

• systemd is now used to look after MysqL instead of MysqLd_safe (which is why you get the -bash: MysqLd_safe: command not found error - it’s not installed)

• The user table structure has changed.

  1. Stop MysqL:
     systemctl stop MysqLd

  2. Set the MysqL environment option
     systemctl set-environment MysqLD_OPTS=”–skip-grant-tables”

  3. Start MysqL usig the options you just set
     systemctl start MysqLd

  4. Login as root
     MysqL -u root

  5. Update the root user password with these MysqL commands
     MysqL> UPDATE MysqL.user SET authentication_string = PASSWORD(‘MyNewPassword’)
     -> WHERE User = ‘root’ AND Host = ‘localhost’;
     MysqL> FLUSH PRIVILEGES;
     MysqL> quit

  6. Stop MysqL
     systemctl stop MysqLd

  7. Unset the MysqL envitroment option so it starts normally next time
     systemctl unset-environment MysqLD_OPTS

  8. Start MysqL normally:
     systemctl start MysqLd

  9. Try to login using your new password:
     MysqL -u root -p

Reference

As it says at http://dev.mysql.com/doc/refman/5.7/en/mysqld-safe.html,

Note

As of MysqL 5.7.6,for MysqL installation using an RPM distribution,server startup and shutdown is managed by systemd on several Linux platforms. On these platforms,MysqLd_safe is no longer installed because it is unnecessary. For more information,see Section 2.5.10,“Managing MysqL Server with systemd”.Which takes you to http://dev.mysql.com/doc/refman/5.7/en/server-management-using-systemd.html where it mentions the systemctl set-environment MysqLD_OPTS= towards the bottom of the page

The password reset commands are at the bottom of
http://dev.mysql.com/doc/refman/5.7/en/resetting-permissions.html