How to Reset the MySQL Root Password on Ubuntu

In this article we will reset the MySQL root password in Ubuntu by starting MySQL with the --skip-grant-tables option.

1. Confirm MySQL version

Firstly, you must confirm which version of MySQL on Ubuntu you are running as commands will be different.

mysql -V

mysql Ver 14.14 Distrib 5.7.25, for Linux (x86_64) using EditLine wrapper

Keep note of your “Distrib”. In the above example, we are on MySQL 5.7. Keep note of this for later.

2. Restart MySQL with skip-grant-table

In order to skip the grant tables and reset the root password, we must first stop the MySQL service.

sudo /etc/init.d/mysql stop

Ensure the directory /var/run/mysqld exists and correct owner set.

sudo mkdir /var/run/mysqld

sudo chown mysql /var/run/mysqld

Now start MySQL with the --skip-grant-tables option. The & is required here.

sudo mysqld_safe --skip-grant-tables&

You should see something similar:

[1] 1283
user@server:~$ 2019-02-12T11:15:59.872516Z mysqld_safe Logging to syslog.
2019-02-12T11:15:59.879527Z mysqld_safe Logging to '/var/log/mysql/error.log'.
2019-02-12T11:15:59.922502Z mysqld_safe Starting mysqld daemon with databases from /var/lib/mysql

You may need to press ENTER to return to the Linux BASH prompt.

3. Change MySQL Root Password

You can now log in to the MySQL root account without a password.

sudo mysql --user=root mysql

Once logged in, you will see the mysql> prompt.
For MySQL 5.7 or above on Ubuntu, run this command to change the root password. Replace your_password_here with your own. (Generate a strong password here)

mysql> update user set authentication_string=PASSWORD('your_password_here') where user='root';

For MySQL 5.6 or below on Ubuntu, run this command to change the root password. Replace your_password_here with your own. (Generate a strong password here)

mysql> update user set Password=PASSWORD('your_password_here') where user='root';

When resetting a root password, you must also change the auth plugin to mysql_native_password

mysql> update user set plugin="mysql_native_password" where User='root';

Flush privileges.

mysql>  flush privileges;

Exit MySQL.

mysql> exit

Make sure all MySQL processes are stopped before starting the service again.

sudo killall -u mysql

Start MySQL again.

sudo /etc/init.d/mysql start

4. Test New Password

Log in to MySQL again and you should now be prompted for a password.

sudo mysql -p -u root

Enter your password. If correct, you should see

Welcome to the MySQL monitor. Commands end with ; or \g.
Your MySQL connection id is 6
Server version: 5.7.25-0ubuntu0.18.04.2 (Ubuntu)

You’re all done!

Source: https://devanswers.co/how-to-reset-mysql-root-password-ubuntu/