mysqld_safe之三言两语
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:
#mysqld_safe --help
Usage: /usr/local/mysql/bin/mysqld_safe [OPTIONS]
The following options may be given as the first argument:
--no-defaults Don't read the system defaults file
--defaults-file=FILE Use the specified defaults file
--defaults-extra-file=FILE Also use defaults from the specified file Other options:
--ledir=DIRECTORY Look for mysqld in the specified directory
--open-files-limit=LIMIT Limit the number of open files
--core-file-size=LIMIT Limit core files to the specified size
--timezone=TZ Set the system timezone
--malloc-lib=LIB Preload shared library LIB if available
--mysqld=FILE Use the specified file as mysqld
--mysqld-version=VERSION Use "mysqld-VERSION" as mysqld
--nice=NICE Set the scheduling priority of mysqld
--plugin-dir=DIR Plugins are under DIR or DIR/VERSION, if
VERSION is given
--skip-kill-mysqld Don't try to kill stray mysqld processes
--syslog Log messages to syslog with 'logger'
--skip-syslog Log messages to error log (default)
--syslog-tag=TAG Pass -t "mysqld-TAG" to 'logger'
--mysqld-safe-log- TYPE must be one of UTC (ISO UTC),
timestamps=TYPE system (ISO local time), hyphen
(hyphenated date a la mysqld 5.6), legacy
(legacy non-ISO mysqld_safe timestamps) All other options are passed to the mysqld program. [root@zlm3 :: /data/mysql/mysql3306]
#
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:
[root@zlm3 :: /usr/local/mysql/bin]
#pkill mysqld [root@zlm3 :: /usr/local/mysql/bin]
#ps aux|grep mysqld
root 0.0 0.0 pts/ R+ : : grep --color=auto mysqld [root@zlm3 :: /usr/local/mysql/bin]
#mysqld_safe --defaults-file=/data/mysql/mysql3306/my.cnf &
[] [root@zlm3 :: /usr/local/mysql/bin]
#--04T05::.758814Z mysqld_safe Logging to '/data/mysql/mysql3306/data/error.log'.
--04T05::.786306Z mysqld_safe Starting mysqld daemon with databases from /data/mysql/mysql3306/data
^C [root@zlm3 :: /usr/local/mysql/bin]
#ps aux|grep mysqld
root 0.1 0.1 pts/ S : : /bin/sh /usr/local/mysql/bin/mysqld_safe --defaults-file=/data/mysql/mysql3306/my.cnf
mysql 1.0 17.4 pts/ Sl : : /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= --pid-file=mysql.pid --socket=/tmp/mysql3306.sock --port=
root 0.0 0.0 pts/ R+ : : grep --color=auto mysqld [root@zlm3 :: /usr/local/mysql/bin]
#
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:
[root@zlm3 :: /usr/local/mysql/bin]
#kill - [root@zlm3 :: /usr/local/mysql/bin]
#/usr/local/mysql/bin/mysqld_safe: line : 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= --pid-file=mysql.pid --socket=/tmp/mysql3306.sock --port= < /dev/null > /dev/null >&
--04T05::.076914Z mysqld_safe Number of processes running now:
--04T05::.083092Z mysqld_safe mysqld restarted
^C [root@zlm3 :: /usr/local/mysql/bin]
#ps aux|grep mysqld
root 0.0 0.1 pts/ S : : /bin/sh /usr/local/mysql/bin/mysqld_safe --defaults-file=/data/mysql/mysql3306/my.cnf
mysql 2.4 17.7 pts/ Sl : : /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= --pid-file=mysql.pid --socket=/tmp/mysql3306.sock --port=
root 0.0 0.0 pts/ R+ : : grep --color=auto mysqld [root@zlm3 :: /usr/local/mysql/bin]
#pkill mysqld [root@zlm3 :: /usr/local/mysql/bin]
#--04T05::.957789Z mysqld_safe mysqld from pid file /data/mysql/mysql3306/data/mysql.pid ended
^C
[]+ Done mysqld_safe --defaults-file=/data/mysql/mysql3306/my.cnf [root@zlm3 :: /usr/local/mysql/bin]
#ps aux|grep mysqld
root 0.0 0.0 pts/ R+ : : grep --color=auto mysqld [root@zlm3 :: /usr/local/mysql/bin]
#
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.
来源: https://dev.mysql.com/doc/refman/8.0/en/mysqld-safe.html
summary:
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.
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