This section provides troubleshooting suggestions for problems starting the server. For additional suggestions for Windows systems, see Section 2.3.8, “Troubleshooting a Microsoft Windows MySQL Server Installation”.
If you have problems starting the server, here are some things to try:
Check the error log to see why the server does not start.
Specify any special options needed by the storage engines you are using.
Make sure that the server knows where to find the data directory.
Make sure that the server can access the data directory. The ownership and permissions of the data directory and its contents must be set such that the server can read and modify them.
Verify that the network interfaces the server wants to use are available.
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
be sure that you have them configured the way you want before
starting the server:
If you are using
InnoDB tables, see
Section 14.11, “InnoDB Configuration”.
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
To specify the location of the data directory explicitly, use
--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
To check the effect of specifying path options, invoke
mysqld with those options followed by the
--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
shell> ./mysqld --basedir=/usr/local --verbose --help
If mysqld is currently running, you can find out what path settings it is using by executing this command:
shell> mysqladmin variables
shell> mysqladmin -h host_name variables
host_name is the name of the MySQL
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:
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
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.
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
5.5\data on Windows,
/usr/local/mysql/data for a Unix/Linux
binary distribution, and
a Unix/Linux source distribution). Look in the data directory
for files with names of the form
host_name is the name of your
server host. Then examine the last few lines of these files. You
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 could not start.
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 5.7, “Running Multiple MySQL Instances on One Machine”.)
If no other server is running, try to execute the command
telnet . (The
default MySQL port number is 3306.) Then press Enter a couple of
times. If you do not get an error message like
Unable to connect to remote host: Connection refused,
some other program is using the TCP/IP port that
mysqld is trying to use. You will 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
will also need to specify the 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, you should
make sure that you have an entry in
/etc/hosts that looks like this: