（3.4）mysql基础深入——mysql.server启动脚本源码阅读与分析

（3.4）mysql基础深入——mysql.server启动脚本源码阅读与分析

my.server主要分为3大部分

【1】变量初始化部分　　【2】函数声明部分　　【3】具体执行部分

#!/bin/sh

#【第1部分，变量初始化部分begin】

#【1.1】指定Mysql安装程序及数据目录的路径，默认是/usr/local/mysql，默认是空的

basedir=/mysql/app/mysql

datadir=/mysql/data//data

# Default value, in seconds, afterwhich the script should timeout waiting

# for server start.

# Value here is overriden by value in my.cnf.

#  means don't wait at all

# Negative numbers mean to wait indefinitely
#【1.2】定义mysql服务启动时间的限制，如果超过900S没有启动，则退出

service_startup_timeout=

# Lock directory for RedHat / SuSE.
#【1.3】操作系统默认在关闭过程一些服务进程的调用，
#【1.3】其实lockdir就是/etc/init.d/ 这个里面启动的，会慢慢一个一个关闭本行里面的进程

lockdir='/var/lock/subsys'

lock_file_path="$lockdir/mysql"

# The following variables are only set for letting mysql.server find things.

# Set some defaults
#【1.4】判断mysql有没有启动

mysqld_pid_file_path=/mysql/data//mysql.pid
#【1.5】判断文件是否存在，然后进行相应的赋值

if test -z "$basedir"

then

  basedir=/mysql/app/mysql

  bindir=/mysql/app/mysql/bin

  if test -z "$datadir"

  then

    datadir=/mysql/data//data

  fi

  sbindir=/mysql/app/mysql/bin

  libexecdir=/mysql/app/mysql/bin

else

  bindir="$basedir/bin"

  if test -z "$datadir"

  then

    datadir="$basedir/data"

  fi

  sbindir="$basedir/sbin"

  libexecdir="$basedir/libexec"

fi

# datadir_set is used to determine if datadir was set (and so should be

# *not* set inside of the --basedir= handler.)

datadir_set=


#【第1部分，变量初始化部分end】

#【第2部分，函数声明部分begin】

#

# Use LSB init script functions for printing messages, if possible

#

#【2.1】本地文件，有些系统可能不存在该文件。可能会在/etc/init.d/init-functions

lsb_functions="/lib/lsb/init-functions"

if test -f $lsb_functions ; then

  . $lsb_functions

else

  log_success_msg()

  {

    echo " SUCCESS! $@"

  }

  log_failure_msg()

  {

    echo " ERROR! $@"

  }

fi


#设置path环境变量

PATH="/sbin:/usr/sbin:/bin:/usr/bin:$basedir/bin"

export PATH


#传脚本运行时的参数

mode=$    # start or stop

[ $# -ge  ] && shift

other_args="$*"   # uncommon, but needed when called from an RPM upgrade action

           # Expected: "--skip-networking --skip-grant-tables"

           # They are not checked here, intentionally, as it is the resposibility

           # of the "spec" file author to give correct arguments only.

case `echo "testing\c"`,`echo -n testing` in

    *c*,-n*) echo_n=   echo_c=     ;;

    *c*,*)   echo_n=-n echo_c=     ;;

    *)       echo_n=   echo_c='\c' ;;

esac


#【2.1】参数解析函数（将参数值赋予变量）
#【2.1】主要涉及参数：--basedir --datadir --pid-file --service-startup-timeout

parse_server_arguments() {

  for arg do

    case "$arg" in

      --basedir=*)  basedir=`echo "$arg" | sed -e 's/^[^=]*=//'`

                    bindir="$basedir/bin"

            if test -z "$datadir_set"; then

              datadir="$basedir/data"

            fi

            sbindir="$basedir/sbin"

            libexecdir="$basedir/libexec"

        ;;

      --datadir=*)  datadir=`echo "$arg" | sed -e 's/^[^=]*=//'`

            datadir_set=

    ;;

      --pid-file=*) mysqld_pid_file_path=`echo "$arg" | sed -e 's/^[^=]*=//'` ;;

      --service-startup-timeout=*) service_startup_timeout=`echo "$arg" | sed -e 's/^[^=]*=//'` ;;

    esac

  done

}

wait_for_pid () {

  verb="$1"           # created | removed

  pid="$2"            # process ID of the program operating on the pid-file

  pid_file_path="$3" # path to the PID file.

  i=

  avoid_race_condition="by checking again"

  while test $i -ne $service_startup_timeout ; do

    case "$verb" in

      'created')

        # wait for a PID-file to pop into existence.

        test -s "$pid_file_path" && i='' && break

        ;;

      'removed')

        # wait for this PID-file to disappear

        test ! -s "$pid_file_path" && i='' && break

        ;;

      *)

        echo "wait_for_pid () usage: wait_for_pid created|removed pid pid_file_path"

        exit

        ;;

    esac

    # if server isn't running, then pid-file will never be updated

    if test -n "$pid"; then

      if kill - "$pid" >/dev/null; then

        :  # the server still runs

      else

        # The server may have exited between the last pid-file check and now.

        if test -n "$avoid_race_condition"; then

          avoid_race_condition=""

          continue  # Check again.

        fi

        # there's nothing that will affect the file.

        log_failure_msg "The server quit without updating PID file ($pid_file_path)."

        return   # not waiting any more.

      fi

    fi

    echo $echo_n ".$echo_c"

    i=`expr $i + `

    sleep

  done

  if test -z "$i" ; then

    log_success_msg

    return

  else

    log_failure_msg

    return

  fi

}

【2.1】参数解析函数end

#【3】主体执行部分
#【3.1】判断my_print_defaults文件的位置

# Get arguments from the my.cnf file,

# the only group, which is read from now on is [mysqld]

if test -x "$bindir/my_print_defaults";  then

  print_defaults="$bindir/my_print_defaults"

else

  # Try to find basedir in /etc/my.cnf

  conf=/etc/my.cnf

  print_defaults=

  if test -r $conf

  then

    subpat='^[^=]*basedir[^=]*=\(.*\)$'

    dirs=`sed -e "/$subpat/!d" -e 's//\1/' $conf`

    for d in $dirs

    do

      d=`echo $d | sed -e 's/[     ]//g'`

      if test -x "$d/bin/my_print_defaults"

      then

        print_defaults="$d/bin/my_print_defaults"

        break

      fi

    done

  fi

  # Hope it's in the PATH ... but I doubt it

  test -z "$print_defaults" && print_defaults="my_print_defaults"

fi

#

# Read defaults file from 'basedir'.   If there is no defaults file there

# check if it's in the old (depricated) place (datadir) and read it from there

#

#【3.2】查找默认的配置文件
extra_args=""

if test -r "$basedir/my.cnf"

then

  extra_args="-e $basedir/my.cnf"

fi

parse_server_arguments `$print_defaults $extra_args mysqld server mysql_server mysql.server`


#【3.3】设置PID文件的路径

#

# Set pid file if not given

#

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


#【3.4】mysql服务脚本start选项

case "$mode" in

  'start')

    # Start daemon

    # Safeguard (relative paths, core dumps..)

    cd $basedir

    echo $echo_n "Starting MySQL"

    if test -x $bindir/mysqld_safe

    then

      # Give extra arguments to mysqld with the my.cnf file. This script

      # may be overwritten at next upgrade.

      $bindir/mysqld_safe --defaults-file=/mysql/data/3306/my.cnf --datadir="$datadir" --pid-file="$mysqld_pid_file_path" $other_args >/dev/null &

      wait_for_pid created "$!" "$mysqld_pid_file_path"; return_value=$?

      # Make lock for RedHat / SuSE

      if test -w "$lockdir"

      then

        touch "$lock_file_path"

      fi

      exit $return_value

    else

      log_failure_msg "Couldn't find MySQL server ($bindir/mysqld_safe)"

    fi

    ;;


#【3.5】 mysql服务停止操作

  'stop')

    # Stop daemon. We use a signal here to avoid having to know the

    # root password.

    if test -s "$mysqld_pid_file_path"

    then

      # signal mysqld_safe that it needs to stop

      touch "$mysqld_pid_file_path.shutdown"

      mysqld_pid=`cat "$mysqld_pid_file_path"`

      if (kill -0 $mysqld_pid 2>/dev/null)

      then

        echo $echo_n "Shutting down MySQL"

        kill $mysqld_pid

        # mysqld should remove the pid file when it exits, so wait for it.

        wait_for_pid removed "$mysqld_pid" "$mysqld_pid_file_path"; return_value=$?

      else

        log_failure_msg "MySQL server process #$mysqld_pid is not running!"

        rm "$mysqld_pid_file_path"

      fi

      # Delete lock for RedHat / SuSE

      if test -f "$lock_file_path"

      then

        rm -f "$lock_file_path"

      fi

      exit $return_value

    else

      log_failure_msg "MySQL server PID file could not be found!"

    fi

    ;;


#【3.6】mysql服务重启

  'restart')

    # Stop the service and regardless of whether it was

    # running or not, start it again.

    if $0 stop  $other_args; then

      $0 start $other_args

    else

      log_failure_msg "Failed to stop running server, so refusing to try to start."

      exit 1

    fi

    ;;

#【3.7】重新加载mysql服务（重新加载复位服务文件，即mysql进程pid文件）

  'reload'|'force-reload')

    if test -s "$mysqld_pid_file_path" ; then

      read mysqld_pid <  "$mysqld_pid_file_path"

      kill -HUP $mysqld_pid && log_success_msg "Reloading service MySQL"

      touch "$mysqld_pid_file_path"

    else

      log_failure_msg "MySQL PID file could not be found!"

      exit 1

    fi

    ;;

#【3.8】mysql服务脚本status选项，查看状态

  'status')

    # First, check to see if pid file exists

    if test -s "$mysqld_pid_file_path" ; then

      read mysqld_pid < "$mysqld_pid_file_path"

      if kill -0 $mysqld_pid 2>/dev/null ; then

        log_success_msg "MySQL running ($mysqld_pid)"

        exit 0

      else

        log_failure_msg "MySQL is not running, but PID file exists"

        exit 1

      fi

    else

      # Try to find appropriate mysqld process

      mysqld_pid=`pidof $libexecdir/mysqld`

#【3.9】mysql多实例服务

      # test if multiple pids exist

      pid_count=`echo $mysqld_pid | wc -w`

      if test $pid_count -gt 1 ; then

        log_failure_msg "Multiple MySQL running but PID file could not be found ($mysqld_pid)"

        exit 5

      elif test -z $mysqld_pid ; then

        if test -f "$lock_file_path" ; then

          log_failure_msg "MySQL is not running, but lock file ($lock_file_path) exists"

          exit 2

        fi

        log_failure_msg "MySQL is not running"

        exit 3

      else

        log_failure_msg "MySQL is running but PID file could not be found"

        exit 4

      fi

    fi

    ;;

    *)

#【3.10】其他情况，如果输入的命令不是如下命令，那么会给一条提示（即echo的提示）

      # usage

      basename=`basename "$0"`

      echo "Usage: $basename  {start|stop|restart|reload|force-reload|status}  [ MySQL server options ]"

      exit 1

    ;;

esac

exit 0