Details of the order in which MySQL reads my.cnf

The order in which MySQL reads my.cnf

1. mysql.server startup method

basedir=/opt/mysql/mysql3315
datadir=/opt/mysql/mysql3315/data

To search, -e will be brought in for parsing when parsing the parameter file

/opt/mysql/mysql3315/bin/my_print_defaults -e /opt/mysql/mysql3315/my.cnf mysqld server mysql_server mysql.server

That is, --defaults-extra-file, the obtained directory includes basedir, datadir, and pid-file, but the pid-file parameter may not exist

Use as follows

if test -z "$mysqld_pid_file_path"
then
  mysqld_pid_file_path=$datadir/`hostname`.pid
else
  case "$mysqld_pid_file_path" in
    /* ) ;;
    * )mysqld_pid_file_path="$datadir/$mysqld_pid_file_path" ;;
  esac
fi

Convert the location and file name. The final parameters are as follows:

/opt/mysql/mysql3315/bin/mysqld_safe --datadir=/opt/mysql/mysql3315/data/ --pid-file=/opt/mysql/mysql3315/data//mgr4.pid

2. mysqld_safe startup method

• Reverse the location of mysqld_safe to get the basedir directory and set MYSQL_HOME to basedir
• Then there are many parameters to be obtained when parsing the parameter file, so they are not listed here.

/opt/mysql/mysql3315/bin/my_print_defaults mysqld server mysql_server mysql.server

Note: -e is not set here because the MYSQL_HOME directory will automatically parse the parameter files below it. The parsing location is shown at the end.

• Start mysqld

nohup /opt/mysql/mysql3315/bin/mysqld --basedir=/opt/mysql/mysql3315 --datadir=/opt/mysql/mysql3315/data 
--plugin-dir=/opt/mysql/mysql3315/lib/plugin --user=mysql 
--log-error=/opt/mysql/mysql3315/logs/mysql3315.err --pid-file=/opt/mysql/mysql3315/data//mgr4.pid 
--socket=/opt/mysql/mysql3315/data/mysql3315.sock --port=3315

Note: If open_files_limits is set, open_file_limits will be used here to overwrite the configuration in the parameter file used by mysqld

• Loop monitoring pid file

After startup, the following loop will be performed. The eval command will be used to block the call to mysqld. If the process exits, it will return and perform a loop judgment. Finally, it will determine whether the pid exists and whether it is a normal shutdown of mysqld. The judgment method is kill -0 pid to determine whether the mysqld process exists. If it doesn't exist, pull it up.

while true
do
  echo 1
  start_time=`date +%M%S`
  eval_log_error "$cmd"

• About loading jemalloc

if [ -n "$mysqld_ld_library_path" ]; then
  new_text="$mysqld_ld_library_path"
  [ -n "$LD_LIBRARY_PATH" ] && new_text="$new_text:$LD_LIBRARY_PATH"
  text="${text}LD_LIBRARY_PATH="`shell_quote_string "$new_text"`' '
fi

• Start it yourself using mysqld_safe
  

```
/home/work/ssd1/mysql/install/bin/mysqld_safe --defaults-file=/home/work/ssd1/mysql/etc/3307/my.cnf --socket=/home/work/ssd1/mysql/sock/3307/mysql.sock --datadir=/home/work/ssd1/mysql/data/3307 --user=mysql &

If you start my_print_defaults like this, it will bring --defaults-file

/opt/mysql/mysql3320/install/bin/my_print_defaults --defaults-file=/home/work/ssd1/mysql/etc/3307/my.cnf --loose-verbose mysqld server

3. About the order in which mysqld and my_print_defaults read my.cnf

In fact, this function init_default_directories function
The order is:

<—defaults-file is read first, and only reads this configuration file, and is the first option>

• /etc/my.cnf
• /etc/mysql/my.cnf
• DEFAULT_SYSCONFDIR my.cnf under compile-time configuration
• MYSQL_HOME setting. mysqld_safe will set MYSQL_HOME and read the following my.cnf.
• --defaults-extra-file settings, my_print_defaults and mysqld are both set by this.
• ~/.my.cnf
• From the order of parsing, the command line parameters will be loaded last.

After parsing is complete, all parameters are listed. If there are multiple parameters with the same name, the last one will take effect.

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