ERROR 2002:
Can't connect to local MySQL server
through socket '/var/lib/mysql/mysql.sock' (2)

ERROR 2003 (HY000): Can't connect to MySQL server
on '123.45.67.89' (113)

Usually these errors mean that there is no mysqld process running on the server machine.
If you are unable to connect to a local MySQL server, check your system's process list using ps on Unix or Task Manager on Windows and start the MySQL server if it is not running.
It's possible that the local socket file has been removed. The default location is /tmp/mysql.sock, and some systems periodically clean out the contents to /tmp. It could even be that another user has deleted this fileinadvertently or otherwisebecause the /tmp directory is often writable by all users. If you experience this issue, change the location of the socket file to another directory owned by the mysql user by adding these lines in my.cnf:

[mysqld]
socket=/path/to/mysql.sock

[client]
socket=/path/to/mysql.sock


To check that mysqld is listening on the port you are expecting, use the netstat command to check that it is indeed accepting network connections. On Unix/Linux use this command:

Linux
shell> netstat l

Windows,
> netstat a | find "LISTENING"


ERROR 1045 (28000):
Access denied for user
'user'@'host' (using password: YES)

You might have supplied an incorrect username or password, or a database name that the given username does not have access to when connecting from the current host. Check the privilege tables in the mysql database to make sure the connection arguments are correct.


ERROR 1040:
Too many connections


The maximum number of simultaneous connections allowed is defined in the max_connections system variable, and the default value is 100. A new value can be set in my.cnf using the following lines:

[mysqld]
max_connections=200

Increasing the max_connections value is usually not the answer. MySQL has exceeded the maximum number of connections for a reason, and you should try to find out why it ran out. You should only increase this value if you are sure your system can support more connections.

In fact, mysqld allows one more connection than the specified number, so a superuser can connect even when the maximum connections have been exceeded. To diagnose problems, run the mysqladmin processlist command and try to work out why there are so many connections.



Error 1030:
Got error 141 from table handler


This error indicates an internal problem with the database table storage file. It can usually be fixed using the myisamchk utility. The error number reported in this message indicates the nature of the problem. Use the perror command from the shell to find the corresponding error message.

shell> perror 141
141 = Duplicate unique key or constraint on write
or update

When you encounter this kind of error, you should stop mysqld and run myisamchk --recover on the corresponding .MYI file.

Sometimes the errors reported are symptomatic of other system issues, as in the following case:

$ perror 28
Error code 28: No space left on device