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

#!/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/3306/data

# Default value, in seconds, afterwhich the script should timeout waiting
# for server start. 
# Value here is overriden by value in my.cnf. 
# 0 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=900

# 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/3306/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/3306/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=$1    # start or stop

[ $# -ge 1 ] && 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 "testingc"`,`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=1
    ;;
      --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=0
  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 1
        ;;
    esac

    # if server isn't running, then pid-file will never be updated
    if test -n "$pid"; then
      if kill -0 "$pid" 2>/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 1  # not waiting any more.
      fi
    fi

    echo $echo_n ".$echo_c"
    i=`expr $i + 1`
    sleep 1

  done

  if test -z "$i" ; then
    log_success_msg
    return 0
  else
    log_failure_msg
    return 1
  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