A.2.2. Can't connect to [local] MySQL server
A MySQL client on Unix can connect to the
mysqld server in two different ways: By using
a Unix socket file to connect through a file in the filesystem
(default /tmp/mysql.sock), or by using
TCP/IP, which connects through a port number. A Unix socket file
connection is faster than TCP/IP, but can be used only when
connecting to a server on the same computer. A Unix socket file
is used if you don't specify a hostname or if you specify the
special hostname localhost.
If the MySQL server is running on Windows 9x or Me, you can
connect only via TCP/IP. If the server is running on Windows NT,
2000, XP, or 2003 and is started with the
--enable-named-pipe option, you can also
connect with named pipes if you run the client on the host where
the server is running. The name of the named pipe is
MySQL by default. If you don't give a
hostname when connecting to mysqld, a MySQL
client first tries to connect to the named pipe. If that doesn't
work, it connects to the TCP/IP port. You can force the use of
named pipes on Windows by using . as the
hostname.
The error (2002) Can't connect to ...
normally means that there is no MySQL server running on the
system or that you are using an incorrect Unix socket filename
or TCP/IP port number when trying to connect to the server.
Start by checking whether there is a process named
mysqld running on your server host. (Use
ps xa | grep mysqld on Unix or the Task
Manager on Windows.) If there is no such process, you should
start the server. See Section 2.9.2.3, “Starting and Troubleshooting the MySQL Server”.
If a mysqld process is running, you can check
it by trying the following commands. The port number or Unix
socket filename might be different in your setup.
host_ip represents the IP number of the
machine where the server is running.
shell> mysqladmin version
shell> mysqladmin variables
shell> mysqladmin -h `hostname` version variables
shell> mysqladmin -h `hostname` --port=3306 version
shell> mysqladmin -h host_ip version
shell> mysqladmin --protocol=socket --socket=/tmp/mysql.sock version
Note the use of backticks rather than forward quotes with the
hostname command; these cause the output of
hostname (that is, the current hostname) to
be substituted into the mysqladmin command.
If you have no hostname command or are
running on Windows, you can manually type the hostname of your
machine (without backticks) following the -h
option. You can also try -h 127.0.0.1 to
connect with TCP/IP to the local host.
Here are some reasons the Can't connect to local MySQL
server error might occur:
mysqld is not running. Check your
operating system's process list to ensure the
mysqld process is present.
You're running a MySQL server on Windows with many TCP/IP
connections to it. If you're experiencing that quite often
your clients get that error, you can find a workaround here:
Section A.2.2.1, “Connection to MySQL Server Failing on Windows”.
-
You are running on a system that uses MIT-pthreads. If you
are running on a system that doesn't have native threads,
mysqld uses the MIT-pthreads package. See
Section 2.1.1, “Operating Systems Supported by MySQL”. However, not all MIT-pthreads
versions support Unix socket files. On a system without
socket file support, you must always specify the hostname
explicitly when connecting to the server. Try using this
command to check the connection to the server:
shell> mysqladmin -h `hostname` version
Someone has removed the Unix socket file that
mysqld uses
(/tmp/mysql.sock by default). For
example, you might have a cron job that
removes old files from the /tmp
directory. You can always run mysqladmin
version to check whether the Unix socket file that
mysqladmin is trying to use really
exists. The fix in this case is to change the
cron job to not remove
mysql.sock or to place the socket file
somewhere else. See
Section A.4.5, “How to Protect or Change the MySQL Unix Socket File”.
-
You have started the mysqld server with
the --socket=/path/to/socket option, but
forgotten to tell client programs the new name of the socket
file. If you change the socket pathname for the server, you
must also notify the MySQL clients. You can do this by
providing the same --socket option when you
run client programs. You also need to ensure that clients
have permission to access the
mysql.sock file. To find out where the
socket file is, you can do:
shell> netstat -ln | grep mysql
See Section A.4.5, “How to Protect or Change the MySQL Unix Socket File”.
You are using Linux and one server thread has died (dumped
core). In this case, you must kill the other
mysqld threads (for example, with
kill or with the
mysql_zap script) before you can restart
the MySQL server. See Section A.4.2, “What to Do If MySQL Keeps Crashing”.
The server or client program might not have the proper
access privileges for the directory that holds the Unix
socket file or the socket file itself. In this case, you
must either change the access privileges for the directory
or socket file so that the server and clients can access
them, or restart mysqld with a
--socket option that specifies a socket
filename in a directory where the server can create it and
where client programs can access it.
If you get the error message Can't connect to MySQL
server on some_host, you can try the following things
to find out what the problem is:
Check whether the server is running on that host by
executing telnet some_host 3306 and
pressing the Enter key a couple of times. (3306 is the
default MySQL port number. Change the value if your server
is listening to a different port.) If there is a MySQL
server running and listening to the port, you should get a
response that includes the server's version number. If you
get an error such as telnet: Unable to connect to
remote host: Connection refused, then there is no
server running on the given port.
If the server is running on the local host, try using
mysqladmin -h localhost variables to
connect using the Unix socket file. Verify the TCP/IP port
number that the server is configured to listen to (it is the
value of the port variable.)
Make sure that your mysqld server was not
started with the --skip-networking option.
If it was, you cannot connect to it using TCP/IP.
Check to make sure that there is no firewall blocking access
to MySQL. Applications such as ZoneAlarm and the Windows XP
personal firewall may need to be configured to allow
external access to a MySQL server.
