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MySQL is an open-source relational database that is free and widely used. It is a good choice if you know that you need a database but don’t know much about all of the available options.
This article describes a basic installation of a MySQL database server on CentOS Linux. You might need to install other packages to let applications use MySQL, like extensions for PHP. Check your application documentation for details.
Note: CentOS 7 has replaced MySQL with MariaDB. To reflect this, instructions for MariaDB procedures are included in this article.
Follow the steps in this section to install the core database server.
Install the MySQL database through the CentOS package manager (yum) by running the following commands at a command prompt:
sudo yum install mysql-server
sudo /sbin/service mysqld start
Run the following command:
sudo /usr/bin/mysql_secure_installation
Press Enter to give no password for root when prompted for it.
To apply some reasonable security to your new MySQL server answer yes to all the prompts. In order, those prompts enable you set the root password, remove anonymous users, disable remote root logins, delete the test database that the installer included, and then reload the privileges so that your changes will take effect.
Install the MariaDB server through the CentOS package manager (yum) by running the following command at a command prompt:
sudo yum install mariadb-server mariadb
If you have iptables enabled and want to connect to the MySQL database from another computer, you must open a port in your server’s firewall (the default port is 3306). You don’t need to do this if the application that uses MySQL is running on the same server.
If you need to open a port, add the following rules in iptables to open port 3306:
iptables -I INPUT -p tcp --dport 3306 -m state --state NEW,ESTABLISHED -j ACCEPT
iptables -I OUTPUT -p tcp --sport 3306 -m state --state ESTABLISHED -j ACCEPT
Note: If you edit the iptables rules file rather than using the command line to add rules, omit the iptables command at the beginning of each line when you add them to the file.
After the installation is complete, you can start the database service by using the commands in this section. If the system is already started, a message informs you that the service is already running.
Use the following command to start MySQL:
sudo /sbin/service mysqld start
Use the following command to stop MySQL:
sudo /sbin/service mysqld stop
Use the following command to start MariaDB:
sudo systemctl start mariadb.service
Use the following command to stop MariaDB:
sudo systemctl stop mariadb.service
To ensure that the database server launches after a reboot, you must enable the chkconfig utility. Use the following commands to do this.
Enable chkconfig on MySQL
sudo chkconfig mysqld on
Enable chkconfig on MariaDB
sudo systemctl enable mariadb.service
There is more than one way to work with a MySQL server, but this article focuses on the most basic and compatible approach: the mysql shell.
At the command prompt, run the following command to launch the mysql shell and enter it as the root user:
/usr/bin/mysql -u root -p
When you’re prompted for a password, enter the one that you set at installation or, if you haven’t set one, press Enter to submit no password.
The following mysql shell prompt should appear:
mysql>
Because you have just installed the MySQL database server, the root account within MySQL has no password set yet. If you are logged in to the database server, set the root password by running the following command:
/usr/bin/mysqladmin -u root password 'new-password'
If you are not logged in to the database server you can remotely set the root password by specifying the hostname of your database server:
/usr/bin/mysqladmin -u root --password='new-password' -h hostname-of-your-server 'new-password'
Note: The rest of this article shows SQL commands in all capitals, but you can also type them in lowercase. The commands are shown capitalized by convention, to make them stand out from field names and other data.
MySQL stores user information in its own database. The name of the database is mysql. Inside that database, the user information is in a table, a dataset, named user. If you want to see what users are set up in the MySQL user table, run the following command:
SELECT User, Host, Password FROM mysql.user;
The following list describes the parts of that command:
SELECT tells MySQL that you are asking for data.
User, Host, Password tells MySQL what fields you want it to look in. Fields are categories for the data in a table. In this case, you are looking for the username, the host associated with the username, and the encrypted password entry.
Note: All SQL queries end in a semicolon. MySQL does not process a query until you type a semicolon.
Following is example output for the preceding query:
SELECT User, Host, Password FROM mysql.user;
+------------------+-----------+------------------------------------------+
| User | Host | Password |
+------------------+-----------+------------------------------------------+
| root | localhost | 2470C0C06DEE42FD1618BB99005ADCA2EC9D1E19 |
| root | demohost | 2470C0C06DEE42FD1618BB99005ADCA2EC9D1E19 |
| root | 127.0.0.1 | 2470C0C06DEE42FD1618BB99005ADCA2EC9D1E19 |
| | % | |
+------------------+-----------+------------------------------------------+
Users are associated with a host, specifically the host to which they connect. The root user in this example is defined for localhost, for the IP address of localhost, and the hostname of the server (demohost in this example). You usually need to set a user for only one host, the one from which you typically connect.
If you’re running your application on the same computer as the MySQL server, the host that it connects to by default is localhost. Any new users that you create must have localhost in their host field.
If your application connects remotely, the host entry that MySQL looks for is the IP address or DNS hostname of the remote computer (the one from which the client is coming).
A special value for the host is %, as you can see in the preceding output for the blank, or anonymous, user (see the following section). The % symbol is a wildcard that applies to any host value.
In the example output, one entry has a host value but no username or password. That’s an anonymous user. When a client connects with no username specified, it’s trying to connect as an anonymous user.
You usually don’t want any anonymous users, but some MySQL installations include one by default. If you see one, you should either delete the user (refer to the username with empty quotes, like ‘’) or set a password for it.
There is a difference between a database server and a database, even though those terms are often used interchangeably. MySQL is a database server, meaning that it tracks databases and controls access to them. The database stores the data, and it is the database that applications are trying to access when they interact with MySQL.
Some applications create a database as part of their setup process, but others require you to create a database and tell the application about it.
To create a database, log in to the mysql shell and run the following command, replacing demodb with the name of the database that you want to create:
CREATE DATABASE demodb;
The database is created. You can verify its creation by running a query to list all databases. The following example shows the query and example output:
SHOW DATABASES;
+--------------------+
| Database |
+--------------------+
| information_schema |
| demodb |
| mysql |
+--------------------+
3 rows in set (0.00 sec)
Use the instructions in this section to add users for the database and grant and revoke privileges.
When applications connect to the database using the root user, they usually have more privileges than they need. You can create a new user that applications can use to connect to the new database. In the following example, a user named demouser is created.
To create a new user, run the following command in the mysql shell:
CREATE USER 'demouser'@'localhost' IDENTIFIED BY 'demopassword';
You can verify that the user was created by running a SELECT query again:
SELECT User, Host, Password FROM mysql.user;
+----------+-----------+------------------------------------------+
| User | Host | Password |
+----------+-----------+------------------------------------------+
| root | localhost | 2470C0C06DEE42FD1618BB99005ADCA2EC9D1E19 |
| root | demohost | 2470C0C06DEE42FD1618BB99005ADCA2EC9D1E19 |
| root | 127.0.0.1 | 2470C0C06DEE42FD1618BB99005ADCA2EC9D1E19 |
| demouser | localhost | 0756A562377EDF6ED3AC45A00B356AAE6D3C6BB6 |
+----------+-----------+------------------------------------------+
Right after you create a new user, it has no privileges. The user can be used to log in to MySQL, but it can’t be used to make any database changes.
Give the user full privileges for your new database by running the following command:
GRANT ALL PRIVILEGES ON demodb.* to demouser@localhost;
Flush the privileges to make the change take effect.
FLUSH PRIVILEGES;
To verify that the privileges were set, run the following command:
SHOW GRANTS FOR 'demouser'@'localhost';
MySQL returns the commands needed to reproduce that user’s privileges if you were to rebuild the server. The USAGE on \*.\* part means that the user gets no privileges on anything by default. That command is overridden by the second command, which is the grant you ran for the new database.
+-----------------------------------------------------------------------------------------------------------------+
| Grants for demouser@localhost |
+-----------------------------------------------------------------------------------------------------------------+
| GRANT USAGE ON *.* TO 'demouser'@'localhost' IDENTIFIED BY PASSWORD '*0756A562377EDF6ED3AC45A00B356AAE6D3C6BB6' |
| GRANT ALL PRIVILEGES ON `demodb`.* TO 'demouser'@'localhost' |
+-----------------------------------------------------------------------------------------------------------------+
2 rows in set (0.00 sec)
Sometimes you might need to revoke (remove) privileges from a user. For example: suppose that you were granting ALL privileges to ‘demouser’@’localhost’, but you accidentally granted privileges to all other databases, too:
+-----------------------------------------------------------------------------------------------------------------+
| Grants for demouser@localhost |
+-----------------------------------------------------------------------------------------------------------------+
| GRANT USAGE ON *.* TO 'demouser'@'localhost' IDENTIFIED BY PASSWORD '*0756A562377EDF6ED3AC45A00B356AAE6D3C6BB6' |
| GRANT ALL PRIVILEGES ON *.* TO 'demouser'@'localhost' |
+-----------------------------------------------------------------------------------------------------------------+
2 rows in set (0.00 sec)
To correct the mistake, you can use a REVOKE statement, followed by GRANT statement to apply the correct privileges.
REVOKE ALL ON *.* FROM demouser@localhost;
GRANT ALL PRIVILEGES ON demodb.* to demouser@localhost;
SHOW GRANTS FOR 'demouser'@'localhost';
+-----------------------------------------------------------------------------------------------------------------+
| Grants for demouser@localhost |
+-----------------------------------------------------------------------------------------------------------------+
| GRANT USAGE ON *.* TO 'demouser'@'localhost' IDENTIFIED BY PASSWORD '*0756A562377EDF6ED3AC45A00B356AAE6D3C6BB6' |
| GRANT ALL PRIVILEGES ON 'demodb'TO 'demouser'@'localhost' |
+-----------------------------------------------------------------------------------------------------------------+
2 rows in set (0.00 sec)
Now your user has the correct privileges, and therefore your database server is slightly more secure (granting privileges like ALL on *.* is deemed as a very bad practice). You should also read official MySQL documentation regarding possible privilege choices, to grant only those privileges truly needed, rather than using ALL.