The order and startup mode of reading configuration files by MySQL as well as the startup principle

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I. the order in which MySQL reads configuration files

Reading order: / etc/my.cnf > / etc/mysql/my.cnf > / usr/etc/my.cnf > ~ / .my.cnf

Command verification:

[root@mysql ~] # mysql-- verbose-- help | grep my.cnf

Order of preference, my.cnf, $MYSQL_TCP_PORT

/ etc/my.cnf / etc/mysql/my.cnf / usr/etc/my.cnf ~ / .my.cnf

II. MySQL startup mode

MySQL is usually started in three ways: mysqld, mysqld_safe, and mysqld_multi (mainly used for multi-instance startup)

The relationship in three ways:

First of all, when we start using service mysqld start or / etc/init.d/mysqld start, we actually use the script mysql.server, which calls mysqld_safe by default to start mysqld, so usually when we check the process after starting mysql, we will find that there are two processes, mysqld and mysqld_safe. These two methods are usually launched in a single instance, but you can also use mysqld to launch multiple instances. While mysqld_multi is used to start multiple instances, it also starts mysql by calling mysqld_safe and mysqld first.

Third, the startup principle of MySQL

The default mysql service launcher is the mysql.server,mysql.server program, which mainly uses two programs and a function, which are my_print_defaults, myslqd_safe and parse_server_arguments.

1. My_print_defaults: read the my.cnf configuration file and pass the output parameters to parse_server_arguments. The program only reads the parameters in [mysqld] in my.cnf.

2. Parse_server_arguments: this function handles the parameter assignment passed by my_print_defaults to-- basedir,-- datadir,-- pid-file,-- server-startup-timeout.

3. The myslqd_safe:mysqld_safe program calls the mysqld program to start the mysql service, and [mysqld_safe] overrides the parameters in the mysqld section.

4. Mysqld_multi will read the parameters under [mysqld_muti] and [mysqldN] in the configuration file. If N needs an integer, it is recommended to use the port number. The configuration of this part will override the configuration in the [mysqld] section.

5. When the mysqld process dies, the mysqld_safe process detects and restarts the mysqld.

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