MySQL 5.7 Reference Manual Including MySQL NDB Cluster 7.5 and NDB Cluster 7.6

B.3.2.9 Communication Errors and Aborted Connections

If connection problems occur such as communication errors or aborted connections, use these sources of information to diagnose problems:

If the log_error_verbosity system variable is set to 3, you might find messages like this in your error log:

[Note] Aborted connection 854 to db: 'employees' user: 'josh'

If a client is unable even to connect, the server increments the Aborted_connects status variable. Unsuccessful connection attempts can occur for the following reasons:

If these kinds of things happen, it might indicate that someone is trying to break into your server! If the general query log is enabled, messages for these types of problems are logged to it.

If a client successfully connects but later disconnects improperly or is terminated, the server increments the Aborted_clients status variable, and logs an Aborted connection message to the error log. The cause can be any of the following:

Other reasons for problems with aborted connections or aborted clients:

See also Section B.3.2.7, “MySQL server has gone away”.