Given that the data directory of the server is empty:

• The server is initialized.
• SSL certificate and key files are generated in the data directory.
• The validate_password plugin is installed and enabled.
• The superuser account 'root'@'localhost' is created. The password for the superuser is set and stored in the error log file.

To reveal the default "root" password:

shell> sudo grep 'temporary password' /var/log/mysqld.log

Change the root password as soon as possible by logging in with the generated temporary password and set a custom password for the superuser account:

shell> mysql -uroot -p 

mysql> ALTER USER 'root'@'localhost' IDENTIFIED BY 'MyNewPass5!'; 

Note: MySQL's validate_password plugin is installed by default. This will require that passwords contain at least one upper case letter, one lower case letter, one digit, and one special character, and that the total password length is at least 8 characters.

if I forget the password then I'll get error.

$ mysql -u root -p    

Enter password:

ERROR 1045 (28000): Access denied for user 'root'@'localhost' (using password: YES)

I tried to solve the issue by first knowing the status:

$ systemctl status mysql.service

mysql.service - MySQL Community Server Loaded: loaded (/lib/systemd/system/mysql.service; enabled; vendor preset: en Active: active (running) since Thu 2017-06-08 14:31:33 IST; 38s ago

Then I used the code mysqld_safe --skip-grant-tables & but I get the error:

mysqld_safe Directory '/var/run/mysqld' for UNIX socket file don't exists.

$ systemctl stop  mysql.service
$ ps -eaf|grep mysql
$ mysqld_safe --skip-grant-tables &

I solved:

$ mkdir -p /var/run/mysqld
$ chown mysql:mysql /var/run/mysqld

Now I use the same code mysqld_safe --skip-grant-tables & and get

mysqld_safe Starting mysqld daemon with databases from /var/lib/mysql

If I use $ mysql -u root I'll get :

Server version: 5.7.18-0ubuntu0.16.04.1 (Ubuntu)

Copyright (c) 2000, 2017, Oracle and/or its affiliates. All rights reserved.

Oracle is a registered trademark of Oracle Corporation and/or its affiliates. Other names may be trademarks of their respective owners.

Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.

mysql>

Now time to change password:

mysql> use mysql
mysql> describe user;

Reading table information for completion of table and column names You can turn off this feature to get a quicker startup with -A

Database changed

mysql> FLUSH PRIVILEGES;
mysql> SET PASSWORD FOR root@'localhost' = PASSWORD('newpwd');

or If you have a mysql root account that can connect from everywhere, you should also do:

UPDATE mysql.user SET Password=PASSWORD('newpwd') WHERE User='root';

Alternate Method:

   USE mysql
   UPDATE user SET Password = PASSWORD('newpwd')
   WHERE Host = 'localhost' AND User = 'root';

And if you have a root account that can access from everywhere:

 USE mysql
 UPDATE user SET Password = PASSWORD('newpwd')
 WHERE Host = '%' AND User = 'root';`enter code here

now need to quit from mysql and stop/start

FLUSH PRIVILEGES;
sudo /etc/init.d/mysql stop
sudo /etc/init.d/mysql start

now again ` mysql -u root -p' and use the new password to get

mysql>