Spec-Zone .ru
спецификации, руководства, описания, API
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Spec-Zone .ru
спецификации, руководства, описания, API
|
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 file system (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 do not specify
a host name or if you specify the special host name localhost.
If the MySQL server is running on Windows, you can connect using TCP/IP. If the server 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 do not give a host name when
connecting to mysqld, a MySQL client first tries to connect to the named
pipe. If that does not work, it connects to the TCP/IP port. You can force the use of named pipes on Windows by
using . as the host name.
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 file name or TCP/IP port number when trying
to connect to the server. You should also check that the TCP/IP port you are using has not been blocked by a
firewall or port blocking service.
The error (2003) Can't connect to MySQL server on ' indicates that the network connection has been
refused. You should check that there is a MySQL server running, that it has network connections enabled, and
that the network port you specified is the one configured on the server. server' (10061)
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 2.10.1.3, "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 file name
might be different in your setup. host_ip represents the IP address of the machine
where the server is running.
shell>mysqladmin versionshell>mysqladmin variablesshell>mysqladmin -h `hostname` version variablesshell>mysqladmin -h `hostname` --port=3306 versionshell>mysqladmin -h host_ip versionshell>mysqladmin --protocol=SOCKET --socket=/tmp/mysql.sock version
Note the use of backticks rather than forward quotation marks with the hostname command; these cause the output of hostname (that is, the current host name) to be substituted into the
mysqladmin command. If you have no hostname command or are running on Windows, you can manually
type the host name 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.
Make sure that the server has not been configured to ignore network connections or (if you are attempting to
connect remotely) that it has not been configured to listen only locally on its network interfaces. If the
server was started with --skip-networking, it will not accept TCP/IP connections at all. If the server
was started with --bind-address=127.0.0.1, it will listen for TCP/IP connections only locally
on the loopback interface and will not accept remote connections.
Check to make sure that there is no firewall blocking access to MySQL. Your firewall may be configured on the basis of the application being executed, or the port number used by MySQL for communication (3306 by default). Under Linux or Unix, check your IP tables (or similar) configuration to ensure that the port has not been blocked. Under Windows, applications such as ZoneAlarm or the Windows XP personal firewall may need to be configured not to block the MySQL port.
Here are some reasons the Can't connect to local MySQL server error might occur:
mysqld is not running on the local host. 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 C.5.2.2.1, "Connection to MySQL Server Failing on Windows".
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 C.5.4.5, "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 path name 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 C.5.4.5, "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 C.5.4.2, "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 file name 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.)
If you are running under Linux and Security-Enhanced Linux (SELinux) is enabled,
make sure you have disabled SELinux protection for the mysqld process.
When you're running a MySQL server on Windows with many TCP/IP connections to it, and you're experiencing
that quite often your clients get a Can't connect to MySQL server error, the
reason might be that Windows does not allow for enough ephemeral (short-lived) ports to serve those
connections.
The purpose of TIME_WAIT is to keep a connection accepting packets even after
the connection has been closed. This is because Internet routing can cause a packet to take a slow route to
its destination and it may arrive after both sides have agreed to close. If the port is in use for a new
connection, that packet from the old connection could break the protocol or compromise personal information
from the original connection. The TIME_WAIT delay prevents this by ensuring
that the port cannot be reused until after some time has been permitted for those delayed packets to arrive.
It is safe to reduce TIME_WAIT greatly on LAN connections because there is
little chance of packets arriving at very long delays, as they could through the Internet with its
comparatively large distances and latencies.
Windows permits ephemeral (short-lived) TCP ports to the user. After any port is closed it will remain in a
TIME_WAIT status for 120 seconds. The port will not be available again until
this time expires. The default range of port numbers depends on the version of Windows, with a more limited
number of ports in older versions:
Windows through Server 2003: Ports in range 1025–5000
Windows Vista, Server 2008, and newer: Ports in range 49152–65535
With a small stack of available TCP ports (5000) and a high number of TCP ports being open and closed over a
short period of time along with the TIME_WAIT status you have a good chance for
running out of ports. There are two ways to address this problem:
Reduce the number of TCP ports consumed quickly by investigating connection pooling or persistent connections where possible
Tune some settings in the Windows registry (see below)
IMPORTANT: The following procedure involves modifying the Windows registry. Before you modify the registry, make sure to back it up and make sure that you understand how to restore the registry if a problem occurs. For information about how to back up, restore, and edit the registry, view the following article in the Microsoft Knowledge Base: .
Start Registry Editor (Regedt32.exe).
Locate the following key in the registry:
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Tcpip\Parameters
On the Edit menu, click Add
Value, and then add the following registry value:
Value Name: MaxUserPortData Type: REG_DWORDValue: 65534
This sets the number of ephemeral ports available to any user. The valid range is between 5000 and 65534 (decimal). The default value is 0x1388 (5000 decimal).
On the Edit menu, click Add
Value, and then add the following registry value:
Value Name: TcpTimedWaitDelayData Type: REG_DWORDValue: 30
This sets the number of seconds to hold a TCP port connection in TIME_WAIT state before closing. The valid range is between 0 (zero)
and 300 (decimal). The default value is 0x78 (120 decimal).
Quit Registry Editor.
Reboot the machine.
Note: Undoing the above should be as simple as deleting the registry entries you've created.