Check the error log to see why the server does not start. Log files are located in the data directory (typically C:\Program Files\MySQL\MySQL Server 8.4\data on Windows, /usr/local/mysql/data for a Unix/Linux binary distribution, and /usr/local/var for a Unix/Linux source distribution). Look in the data directory for files with names of the form host_name.err and host_name.log, where host_name is the name of your server host. Then examine the last few lines of these files. Use tail to display them:

$> tail host_name.err
$> tail host_name.log

Specify any special options needed by the storage engines you are using. You can create a my.cnf file and specify startup options for the engines that you plan to use. If you are going to use storage engines that support transactional tables (InnoDB, NDB), be sure that you have them configured the way you want before starting the server. If you are using InnoDB tables, see Section 17.8, “InnoDB Configuration” for guidelines and Section 17.14, “InnoDB Startup Options and System Variables” for option syntax.

Although storage engines use default values for options that you omit, Oracle recommends that you review the available options and specify explicit values for any options whose defaults are not appropriate for your installation.

Make sure that the server knows where to find the data directory. The mysqld server uses this directory as its current directory. This is where it expects to find databases and where it expects to write log files. The server also writes the pid (process ID) file in the data directory.

The default data directory location is hardcoded when the server is compiled. To determine what the default path settings are, invoke mysqld with the --verbose and --help options. If the data directory is located somewhere else on your system, specify that location with the --datadir option to mysqld or mysqld_safe, on the command line or in an option file. Otherwise, the server does not work properly. As an alternative to the --datadir option, you can specify mysqld the location of the base directory under which MySQL is installed with the --basedir, and mysqld looks for the data directory there.

To check the effect of specifying path options, invoke mysqld with those options followed by the --verbose and --help options. For example, if you change location to the directory where mysqld is installed and then run the following command, it shows the effect of starting the server with a base directory of /usr/local:

$> ./mysqld --basedir=/usr/local --verbose --help

You can specify other options such as --datadir as well, but --verbose and --help must be the last options.

Once you determine the path settings you want, start the server without --verbose and --help.

If mysqld is currently running, you can find out what path settings it is using by executing this command:

$> mysqladmin variables

Or:

$> mysqladmin -h host_name variables

host_name is the name of the MySQL server host.

Make sure that the server can access the data directory. The ownership and permissions of the data directory and its contents must allow the server to read and modify them.

If you get Errcode 13 (which means Permission denied) when starting mysqld, this means that the privileges of the data directory or its contents do not permit server access. In this case, you change the permissions for the involved files and directories so that the server has the right to use them. You can also start the server as root, but this raises security issues and should be avoided.

Change location to the data directory and check the ownership of the data directory and its contents to make sure the server has access. For example, if the data directory is /usr/local/mysql/var, use this command:

$> ls -la /usr/local/mysql/var

If the data directory or its files or subdirectories are not owned by the login account that you use for running the server, change their ownership to that account. If the account is named mysql, use these commands:

$> chown -R mysql /usr/local/mysql/var
$> chgrp -R mysql /usr/local/mysql/var

Even with correct ownership, MySQL might fail to start up if there is other security software running on your system that manages application access to various parts of the file system. In this case, reconfigure that software to enable mysqld to access the directories it uses during normal operation.

Verify that the network interfaces the server wants to use are available.

If either of the following errors occur, it means that some other program (perhaps another mysqld server) is using the TCP/IP port or Unix socket file that mysqld is trying to use:

Can't start server: Bind on TCP/IP port: Address already in use
Can't start server: Bind on unix socket...

Use ps to determine whether you have another mysqld server running. If so, shut down the server before starting mysqld again. (If another server is running, and you really want to run multiple servers, you can find information about how to do so in Section 7.8, “Running Multiple MySQL Instances on One Machine”.)

If no other server is running, execute the command telnet your_host_name tcp_ip_port_number. (The default MySQL port number is 3306.) Then press Enter a couple of times. If you do not get an error message like telnet: Unable to connect to remote host: Connection refused, some other program is using the TCP/IP port that mysqld is trying to use. Track down what program this is and disable it, or tell mysqld to listen to a different port with the --port option. In this case, specify the same non-default port number for client programs when connecting to the server using TCP/IP.

Another reason the port might be inaccessible is that you have a firewall running that blocks connections to it. If so, modify the firewall settings to permit access to the port.

If the server starts but you cannot connect to it, make sure that you have an entry in /etc/hosts that looks like this:

127.0.0.1       localhost

If you cannot get mysqld to start, try to make a trace file to find the problem by using the --debug option. See Section 7.9.4, “The DBUG Package”.