mysqld_safe之三言兩語

    today,one buddy in IMG wechat group 2 asked "why i've installed the MySQL 5.7 on linux server,but there's no mysqld_safe command at all?"so,here i'd like to post this article to say something about it.first of all,let's see the command parameter and usage:

 1 #mysqld_safe --help
 2 Usage: /usr/local/mysql/bin/mysqld_safe [OPTIONS]
 3  The following options may be given as the first argument:
 4   --no-defaults              Don't read the system defaults file
 5   --defaults-file=FILE       Use the specified defaults file
 6   --defaults-extra-file=FILE Also use defaults from the specified file
 7 
 8  Other options:
 9   --ledir=DIRECTORY          Look for mysqld in the specified directory
10   --open-files-limit=LIMIT   Limit the number of open files
11   --core-file-size=LIMIT     Limit core files to the specified size
12   --timezone=TZ              Set the system timezone
13   --malloc-lib=LIB           Preload shared library LIB if available
14   --mysqld=FILE              Use the specified file as mysqld
15   --mysqld-version=VERSION   Use "mysqld-VERSION" as mysqld
16   --nice=NICE                Set the scheduling priority of mysqld
17   --plugin-dir=DIR           Plugins are under DIR or DIR/VERSION, if
18                              VERSION is given
19   --skip-kill-mysqld         Don't try to kill stray mysqld processes
20   --syslog                   Log messages to syslog with 'logger'
21   --skip-syslog              Log messages to error log (default)
22   --syslog-tag=TAG           Pass -t "mysqld-TAG" to 'logger'
23   --mysqld-safe-log-         TYPE must be one of UTC (ISO 8601 UTC),
24     timestamps=TYPE          system (ISO 8601 local time), hyphen
25                              (hyphenated date a la mysqld 5.6), legacy
26                              (legacy non-ISO 8601 mysqld_safe timestamps)
27 
28 All other options are passed to the mysqld program.
29 
30 [root@zlm3 07:43:01 /data/mysql/mysql3306]
31 #

    the most simplest usage of mysqld_safe way is to just use '--defaults-file' to specify which "my.cnf" you want to use,just like:

 1 [root@zlm3 07:54:10 /usr/local/mysql/bin]
 2 #pkill mysqld
 3 
 4 [root@zlm3 07:54:40 /usr/local/mysql/bin]
 5 #ps aux|grep mysqld
 6 root      6302  0.0  0.0 112640   960 pts/0    R+   07:54   0:00 grep --color=auto mysqld
 7 
 8 [root@zlm3 07:54:51 /usr/local/mysql/bin]
 9 #mysqld_safe --defaults-file=/data/mysql/mysql3306/my.cnf &
10 [1] 6307
11 
12 [root@zlm3 07:55:21 /usr/local/mysql/bin]
13 #2018-06-04T05:55:21.758814Z mysqld_safe Logging to '/data/mysql/mysql3306/data/error.log'.
14 2018-06-04T05:55:21.786306Z mysqld_safe Starting mysqld daemon with databases from /data/mysql/mysql3306/data
15 ^C
16 
17 [root@zlm3 07:55:35 /usr/local/mysql/bin]
18 #ps aux|grep mysqld
19 root      6307  0.1  0.1 113252  1628 pts/0    S    07:55   0:00 /bin/sh /usr/local/mysql/bin/mysqld_safe --defaults-file=/data/mysql/mysql3306/my.cnf
20 mysql     7328  1.0 17.4 1069424 177592 pts/0  Sl   07:55   0:00 /usr/local/mysql/bin/mysqld --defaults-file=/data/mysql/mysql3306/my.cnf --basedir=/usr/local/mysql --datadir=/data/mysql/mysql3306/data --plugin-dir=/usr/local/mysql/lib/plugin --user=mysql --log-error=error.log --open-files-limit=65535 --pid-file=mysql.pid --socket=/tmp/mysql3306.sock --port=3306
21 root      7361  0.0  0.0 112640   960 pts/0    R+   07:55   0:00 grep --color=auto mysqld
22 
23 [root@zlm3 07:55:44 /usr/local/mysql/bin]
24 #

    here we can see,there're two processes running,one is mysqld_safe,another one is the mysqld.even if you use "kill -9 7328" to stop the mysqld process,but subsequently you'll find that the mysqld will startup again soon,unless you kill mysqld process by using "pkill mysqld" as below:

 1 [root@zlm3 07:55:44 /usr/local/mysql/bin]
 2 #kill -9 7328
 3 
 4 [root@zlm3 07:57:15 /usr/local/mysql/bin]
 5 #/usr/local/mysql/bin/mysqld_safe: line 198:  7328 Killed                  nohup /usr/local/mysql/bin/mysqld --defaults-file=/data/mysql/mysql3306/my.cnf --basedir=/usr/local/mysql --datadir=/data/mysql/mysql3306/data --plugin-dir=/usr/local/mysql/lib/plugin --user=mysql --log-error=error.log --open-files-limit=65535 --pid-file=mysql.pid --socket=/tmp/mysql3306.sock --port=3306 < /dev/null > /dev/null 2>&1
 6 2018-06-04T05:57:15.076914Z mysqld_safe Number of processes running now: 0
 7 2018-06-04T05:57:15.083092Z mysqld_safe mysqld restarted
 8 ^C
 9 
10 [root@zlm3 07:57:20 /usr/local/mysql/bin]
11 #ps aux|grep mysqld
12 root      6307  0.0  0.1 113256  1676 pts/0    S    07:55   0:00 /bin/sh /usr/local/mysql/bin/mysqld_safe --defaults-file=/data/mysql/mysql3306/my.cnf
13 mysql     7385  2.4 17.7 1081288 180624 pts/0  Sl   07:57   0:00 /usr/local/mysql/bin/mysqld --defaults-file=/data/mysql/mysql3306/my.cnf --basedir=/usr/local/mysql --datadir=/data/mysql/mysql3306/data --plugin-dir=/usr/local/mysql/lib/plugin --user=mysql --log-error=error.log --open-files-limit=65535 --pid-file=mysql.pid --socket=/tmp/mysql3306.sock --port=3306
14 root      7419  0.0  0.0 112640   960 pts/0    R+   07:57   0:00 grep --color=auto mysqld
15 
16 [root@zlm3 07:57:24 /usr/local/mysql/bin]
17 #pkill mysqld
18 
19 [root@zlm3 07:57:37 /usr/local/mysql/bin]
20 #2018-06-04T05:57:38.957789Z mysqld_safe mysqld from pid file /data/mysql/mysql3306/data/mysql.pid ended
21 ^C
22 [1]+  Done                    mysqld_safe --defaults-file=/data/mysql/mysql3306/my.cnf
23 
24 [root@zlm3 07:57:48 /usr/local/mysql/bin]
25 #ps aux|grep mysqld
26 root      7439  0.0  0.0 112640   956 pts/0    R+   07:57   0:00 grep --color=auto mysqld
27 
28 [root@zlm3 07:57:55 /usr/local/mysql/bin]
29 #

For some Linux platforms, MySQL installation from RPM or Debian packages includes systemd support for managing MySQL server startup and shutdown. On these platforms, mysqld_safe is not installed because it is unnecessary. For more information, see Section 2.5.9, “Managing MySQL Server with systemd”.

    therefore,if you want the mysqld_safe feature,i rather recommend you to install MySQL server with binary distribution instead of rpm distribution.

4.3.2 mysqld_safe — MySQL Server Startup Script

mysqld_safe is the recommended way to start a mysqld server on Unix. mysqld_safe adds some safety features such as restarting the server when an error occurs and logging runtime information to an error log. A description of error logging is given later in this section.

 來源： https://dev.mysql.com/doc/refman/8.0/en/mysqld-safe.html 

    another buddy in zst techique wechat group said that it will be messy in troubleshooting while using mysqld_safe to startup mysqld,'cause in some case,the mysqld_safe may lead to the ceaseless restarting of mysqld.furthermore,it may destroy the evidences and logs which can be diagnosted by DBAs.anyhow,in my opinion it depends:

• if the bussines continuity is the first thing you need to consider,i recommend to use mysqld_safe method.
• if your monitor system is strong enough or the application on the MySQL server is not so important such as enterprise management system,BBS system,i recommend to use mysqld method.