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 *note 'kill': kill. command. Some command interpreters associate certain key sequences with signals, such as 'Control+C' to send a 'SIGINT' signal. This section describes how the MySQL server and client programs respond to signals.
*note server-signal-response::
*note client-signal-response::
Server Response to Signals
*note 'mysqld': mysqld. responds to signals as follows:
'SIGTERM' causes the server to shut down. This is like executing a *note 'SHUTDOWN': shutdown. statement without having to connect to the server (which for shutdown requires an account that has the 'SHUTDOWN' privilege).
'SIGHUP' causes 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 *note 'FLUSH': flush. statement. 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. The server also writes a status report to the error log that has this format:
Status information:
Current dir: /var/mysql/data/
Running threads: 4 Stack size: 262144
Current locks:
lock: 0x7f742c02c0e0:
lock: 0x2cee2a20:
:
lock: 0x207a080:
Key caches:
default
Buffer_size: 8388608
Block_size: 1024
Division_limit: 100
Age_limit: 300
blocks used: 4
not flushed: 0
w_requests: 0
writes: 0
r_requests: 8
reads: 4
handler status:
read_key: 13
read_next: 4
read_rnd 0
read_first: 13
write: 1
delete 0
update: 0
Table status:
Opened tables: 121
Open tables: 114
Open files: 18
Open streams: 0
Memory status:
<malloc version="1">
<heap nr="0">
<sizes>
<size from="17" to="32" total="32" count="1"/>
<size from="33" to="48" total="96" count="2"/>
<size from="33" to="33" total="33" count="1"/>
<size from="97" to="97" total="6014" count="62"/>
<size from="113" to="113" total="904" count="8"/>
<size from="193" to="193" total="193" count="1"/>
<size from="241" to="241" total="241" count="1"/>
<size from="609" to="609" total="609" count="1"/>
<size from="16369" to="16369" total="49107" count="3"/>
<size from="24529" to="24529" total="98116" count="4"/>
<size from="32689" to="32689" total="32689" count="1"/>
<unsorted from="241" to="7505" total="7746" count="2"/>
</sizes>
<total type="fast" count="3" size="128"/>
<total type="rest" count="84" size="195652"/>
<system type="current" size="690774016"/>
<system type="max" size="690774016"/>
<aspace type="total" size="690774016"/>
<aspace type="mprotect" size="690774016"/>
</heap>
:
<total type="fast" count="85" size="5520"/>
<total type="rest" count="116" size="316820"/>
<total type="mmap" count="82" size="939954176"/>
<system type="current" size="695717888"/>
<system type="max" size="695717888"/>
<aspace type="total" size="695717888"/>
<aspace type="mprotect" size="695717888"/>
</malloc>
Events status:
LLA = Last Locked At LUA = Last Unlocked At
WOC = Waiting On Condition DL = Data Locked
Event scheduler status:
State : INITIALIZED
Thread id : 0
LLA : n/a:0
LUA : n/a:0
WOC : NO
Workers : 0
Executed : 0
Data locked: NO
Event queue status:
Element count : 0
Data locked : NO
Attempting lock : NO
LLA : init_queue:95
LUA : init_queue:103
WOC : NO
Next activation : never'SIGINT' normally is ignored by the server. Starting the server with the '--gdb' option installs an interrupt handler for 'SIGINT' for debugging purposes. See *note using-gdb-on-mysqld::.
Client Response to Signals
MySQL client programs respond to signals as follows:
The *note 'mysql': 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-ignore' option to ignore 'SIGINT' signals.
Client programs that use the MySQL client library block 'SIGPIPE' signals by default. These variations are possible:
* Client can install their own 'SIGPIPE' handler to override the
default behavior. See Writing C API Threaded Client Programs
(https://dev.mysql.com/doc/c-api/5.7/en/c-api-threaded-clients.html).
* Clients can prevent installation of 'SIGPIPE' handlers by
specifying the 'CLIENT_IGNORE_SIGPIPE' option to
'mysql_real_connect()'
(https://dev.mysql.com/doc/c-api/5.7/en/mysql-real-connect.html)
at connect time. See mysql_real_connect()
(https://dev.mysql.com/doc/c-api/5.7/en/mysql-real-connect.html).File: manual.info.tmp, Node: server-administration, Next: security, Prev: programs, Up: Top
5 MySQL Server Administration *****************************
Menu:
debugging-mysql:: Debugging MySQL
MySQL Server (*note 'mysqld': mysqld.) is the main program that does most of the work in a MySQL installation. This chapter provides an overview of MySQL Server and covers general server administration:
Server configuration
The data directory, particularly the 'mysql' system database
The server log files
Management of multiple servers on a single machine
For additional information on administrative topics, see also:
*note security::
*note backup-and-recovery::
*note replication::
File: manual.info.tmp, Node: mysqld-server, Next: data-directory, Prev: server-administration, Up: server-administration