Can't open and lock privilege tables: Table 'mysql.user' doesn't exist

You have to initialize the data directory by running the following command

mysqld --initialize [with random root password]

mysqld --initialize-insecure [with blank root password]

The mysql_install_db script also needs the datadir parameter:

mysql_install_db --user=root --datadir=$db_datapath

On Maria DB you use the install script mysql_install_db to install and initialize. In my case I use an environment variable for the data path. Not only does mysqld need to know where the data is (specified via commandline), but so does the install script.

mysqld --initialize to initialize the data directory then mysqld &

If you had already launched mysqld& without mysqld --initialize you might have to delete all files in your data directory

You can also modify /etc/my.cnf to add a custom path to your data directory like this :

[mysqld]
...  
datadir=/path/to/directory

As suggested above, i had similar issue with mysql-5.7.18,
i did this in this way

1. Executed this command from "MYSQL_HOME\bin\mysqld.exe --initialize-insecure"
2. then started "MYSQL_HOME\bin\mysqld.exe"
3. Connect workbench to this localhost:3306 with username 'root'
4. then executed this query "SET PASSWORD FOR 'root'@'localhost' = 'root';"

password was also updated successfully.