The server error log can be a useful source of information
about connection problems. See Section 5.3.1, “The Error Log”.
Starting with MySQL 3.23.40, if you start the server with the
MySQL 4.0.3 on), you might find messages like this in your
010301 14:38:23 Aborted connection 854 to db: 'users' user: 'josh'
If a client successfully connects but later disconnects
improperly or is terminated, the server increments the
variable, and logs an Aborted
connection message to the error log. The cause can
be any of the following:
The client program did not call
The client program ended abruptly in the middle of a data transfer.
If a client is unable even to connect, the server increments
variable. Unsuccessful connection attempts can occur for the
If these kinds of things happen, it might indicate that someone is trying to break into your server! Messages for these types of problems are logged to the general query log if it is enabled.
Other reasons for problems with aborted clients or aborted connections:
Use of Ethernet protocol with Linux, both half and full duplex. Many Linux Ethernet drivers have this bug. You should test for this bug by transferring a huge file using FTP between the client and server machines. If a transfer goes in burst-pause-burst-pause mode, you are experiencing a Linux duplex syndrome. Switch the duplex mode for both your network card and hub/switch to either full duplex or to half duplex and test the results to determine the best setting.
A problem with the thread library that causes interrupts on reads.
Badly configured TCP/IP.
Faulty Ethernets, hubs, switches, cables, and so forth. This can be diagnosed properly only by replacing hardware.