This section provides troubleshooting suggestions for problems starting the server on Unix. If you are using Windows, see Troubleshooting a MySQL Installation Under Windows.

If you have problems starting the server, here are some things to try:

Some storage engines have options that control their behavior. 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:

MySQL Enterprise.  For expert advice on start-up options appropriate to your circumstances, subscribe to The MySQL Enterprise Monitor. For more information, see http://www.mysql.com/products/enterprise/advisors.html.

Storage engines will use default option values if you specify none, but it is recommended that you review the available options and specify explicit values for those for which the defaults are not appropriate for your installation.

When the mysqld server starts, it changes location to the data 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 data directory location is hardwired in when the server is compiled. This is where the server looks for the data directory by default. If the data directory is located somewhere else on your system, the server will not work properly. You can determine what the default path settings are by invoking mysqld with the --verbose and --help options.

If the default locations don't match the MySQL installation layout on your system, you can override them by specifying options to mysqld or mysqld_safe on the command line or in an option file.

To specify the location of the data directory explicitly, use the --datadir option. However, normally you can tell mysqld the location of the base directory under which MySQL is installed and it looks for the data directory there. You can do this with the --basedir option.

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 into 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:

shell> ./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:

shell> mysqladmin variables

Or:

shell> mysqladmin -h host_name variables

host_name is the name of the MySQL server host.

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 allow the 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.

On Unix, change location into 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:

shell> 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:

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

If it possible that even with correct ownership, MySQL may 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, you may need to reconfigure that software to enable mysqld to access the directories it uses during normal operation.

If the server fails to start up correctly, check the error log. Log files are located in the data directory (typically C:\Program Files\MySQL\MySQL Server 5.1\data on Windows, /usr/local/mysql/data for a Unix binary distribution, and /usr/local/var for a Unix 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. On Unix, you can use tail to display them:

shell> tail host_name.err
shell> tail host_name.log

The error log should contain information that indicates why the server couldn't start.

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 Running Multiple MySQL Servers on the Same Machine.)

If no other server is running, try to 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 don't 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. You'll need to track down what program this is and disable it, or else tell mysqld to listen to a different port with the --port option. In this case, you'll also need to specify the port number for client programs when connecting to the server via 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 allow access to the port.

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

127.0.0.1       localhost

This problem occurs only on systems that do not have a working thread library and for which MySQL must be configured to use MIT-pthreads.

If you cannot get mysqld to start, you can try to make a trace file to find the problem by using the --debug option. See MySQL Internals: Porting.