On Unix and Unix-like systems, a process can be the recipient of
signals sent to it by the
root system account
or the system account that owns the process. Signals can be sent
using the kill command. Some command
interpreters associate certain key sequences with signals, such as
Control+C to send a
signal. This section describes how the MySQL server and client
programs respond to signals.
mysqld responds to signals as follows:
SIGHUPcauses the server to reload the grant tables and to flush tables, logs, the thread cache, and the host cache. These actions are like various forms of the
FLUSHstatement. Sending the signal enables the flush operations to be performed without having to connect to the server, which requires a MySQL account that has privileges sufficient for those operations.
SIGUSR1causes the server to flush the error log, general query log, and slow query log. One use for
SIGUSR1is to implement log rotation without having to connect to the server, which requires a MySQL account that has privileges sufficient for those operations. For information about log rotation, see Section 5.4.6, “Server Log Maintenance”.
The server response to
SIGUSR1is a subset of the response to
SIGUSR1to be used as a more “lightweight” signal that flushes certain logs without the other
SIGHUPeffects such as flushing the thread and host caches and writing a status report to the error log.
MySQL client programs respond to signals as follows:
The mysql client interprets
SIGINT(typically the result of typing Control+C) as instruction to interrupt the current statement if there is one, or to cancel any partial input line otherwise. This behavior can be disabled using the
--sigint-ignoreoption to ignore
Client programs that use the MySQL client library block
SIGPIPEsignals by default. These variations are possible: