分类： database

Step 1 — Identifying the Database Version
Most modern Linux distributions ship with either MySQL or MariaDB, a popular drop-in replacement which is fully compatible with MySQL. Depending on the database used and its version, you’ll need to use different commands to recover the root password.
You can check your version with the following command:

mysql –version
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You’ll see some output like this with MySQL:

MySQL output
mysql Ver 14.14 Distrib 5.7.16, for Linux (x86_64) using EditLine wrapper
Or output like this for MariaDB:

MariaDB output
mysql Ver 15.1 Distrib 5.5.52-MariaDB, for Linux (x86_64) using readline 5.1
Make note of which database and which version you’re running, as you’ll use them later. Next, you need to stop the database so you can access it manually.
Step 2 — Stopping the Database Server
To change the root password, you have to shut down the database server beforehand.
You can do that for MySQL with:

sudosystemctl stop mysql
And for MariaDB wtih:

sudosystemctl stop mariadb

After the database server is stopped, you’ll access it manually to reset the root password.
Step 3 — Restarting the Database Server Without Permission Checking
If you run MySQL and MariaDB without loading information about user privileges, it will allow you to access the database command line with root privileges without providing a password. This will allow you to gain access to the database without knowing it.
To do this, you need to stop the database from loading the grant tables, which store user privilege information. Because this is a bit of a security risk, you should also skip networking as well to prevent other clients from connecting.
Start the database without loading the grant tables or enabling networking:

sudomysqld_safe –skip-grant-tables –skip-networking &

The ampersand at the end of this command will make this process run in the background so you can continue to use your terminal.
Now you can connect to the database as the root user, which should not ask for a password.

mysql -uroot
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You’ll immediately see a database shell prompt instead.
MySQL prompt
Type ‘help;’ or ‘\h’ for help. Type ‘\c’ to clear the current input statement.
mysql>
MariaDB prompt
Type ‘help;’ or ‘\h’ for help. Type ‘\c’ to clear the current input statement.
MariaDB [(none)]>
Now that you have root access, you can change the root password.
Step 4 — Changing the Root Password
One simple way to change the root password for modern versions of MySQL is using the ALTER USER command. However, this command won’t work right now because the grant tables aren’t loaded.
Let’s tell the database server to reload the grant tables by issuing the FLUSH PRIVILEGES command.

FLUSH PRIVILEGES;非常关键，必须先执行这个，然后执行后面的语句才有效
Now we can actually change the root password.
For MySQL 5.7.6 and newer as well as MariaDB 10.1.20 and newer, use the following command.

ALTER USER’root’@’localhost’IDENTIFIED BY ‘new_password’;
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For MySQL 5.7.5 and older as well as MariaDB 10.1.20 and older, use:

SET PASSWORD FOR ‘root’@’localhost’=PASSWORD(‘new_password’);
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Make sure to replace new_password with your new password of choice.
Note: If the ALTER USER command doesn’t work, it’s usually indicative of a bigger problem. However, you can try UPDATE … SET to reset the root password instead.

UPDATE mysql.user SET authentication_string =PASSWORD(‘new_password’)WHERE User =’root’AND Host =’localhost’;
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Remember to reload the grant tables after this.
In either case, you should see confirmation that the command has been successfully executed.

Output
Query OK, 0 rows affected (0.00 sec)
The password has been changed, so you can now stop the manual instance of the database server and restart it as it was before.
Step 5 — Restart the Database Server Normally
First, stop the instance of the database server that you started manually in Step 3. This command searches for the PID, or process ID, of MySQL or MariaDB process and sends SIGTERM to tell it to exit smoothly after performing clean-up operations. You can learn more in this Linux process management tutorial.
For MySQL, use:

sudokillcat/var/run/mysqld/mysqld.pid
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For MariaDB, use:

sudokill/var/run/mariadb/mariadb.pid
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Then, restart the service using systemctl.
For MySQL, use:

sudosystemctl start mysql
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For MariaDB, use:

sudosystemctl start mariadb
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Now you can confirm that the new password has been applied correctly by running:

mysql -uroot -p
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The command should now prompt for the newly assigned password. Enter it, and you should gain access to the database prompt as expected.
Conclusion
You now have administrative access to the MySQL or MariaDB server restored. Make sure the new root password you choose is strong and secure and keep it in safe place.