深度解析MySQL启动时报“The server quit without updating PID file”错误的原因

时间：2022-08-09 06:29:29

很多童鞋在启动mysql的时候，碰到过这个错误，

首先，澄清一点，出现这个错误的前提是：通过服务脚本来启动mysql。通过mysqld_safe或mysqld启动mysql实例并不会报这个错误。

那么，出现这个错误的原因具体是什么呢？

哈哈，对分析过程不care的童鞋可直接跳到文末的总结部分~

总结

下面，来分析下mysql的服务启动脚本

脚本完整内容如下：

#!/bin/sh

# Copyright Abandoned  TCX DataKonsult AB & Monty Program KB & Detron HB

# This file is public domain and comes with NO WARRANTY of any kind

# MySQL daemon start/stop script.

# Usually this is put in /etc/init.d (at least on machines SYSV R4 based

# systems) and linked to /etc/rc3.d/S99mysql and /etc/rc0.d/K01mysql.

# When this is done the mysql server will be started when the machine is

# started and shut down when the systems goes down.

# Comments to support chkconfig on RedHat Linux

# chkconfig:

# description: A very fast and reliable SQL database engine.

# Comments to support LSB init script conventions

### BEGIN INIT INFO

# Provides: mysql

# Required-Start: $local_fs $network $remote_fs

# Should-Start: ypbind nscd ldap ntpd xntpd

# Required-Stop: $local_fs $network $remote_fs

# Default-Start:

# Default-Stop:

# Short-Description: start and stop MySQL

# Description: MySQL is a very fast and reliable SQL database engine.

### END INIT INFO

# If you install MySQL on some other places than /usr/local/mysql, then you

# have to do one of the following things for this script to work:

#

# - Run this script from within the MySQL installation directory

# - Create a /etc/my.cnf file with the following information:

#   [mysqld]

#   basedir=<path-to-mysql-installation-directory>

# - Add the above to any other configuration file (for example ~/.my.ini)

#   and copy my_print_defaults to /usr/bin

# - Add the path to the mysql-installation-directory to the basedir variable

#   below.

#

# If you want to affect other MySQL variables, you should make your changes

# in the /etc/my.cnf, ~/.my.cnf or other MySQL configuration files.

# If you change base dir, you must also change datadir. These may get

# overwritten by settings in the MySQL configuration files.

basedir=

datadir=

# 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

service_startup_timeout=

# Lock directory for RedHat / SuSE.

lockdir='/var/lock/subsys'

lock_file_path="$lockdir/mysql"

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

# Set some defaults

mysqld_pid_file_path=

if test -z "$basedir"

then

  basedir=/usr/local/mysql

  bindir=/usr/local/mysql/bin

  if test -z "$datadir"

  then

    datadir=/usr/local/mysql/data

  fi

  sbindir=/usr/local/mysql/bin

  libexecdir=/usr/local/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=

#

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

#

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

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

export PATH

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

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

}

# Get arguments from the my.cnf file,

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

if test -x ./bin/my_print_defaults

then

  print_defaults="./bin/my_print_defaults"

elif test -x $bindir/my_print_defaults

then

  print_defaults="$bindir/my_print_defaults"

elif test -x $bindir/mysql_print_defaults

then

  print_defaults="$bindir/mysql_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

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

      then

        print_defaults="$d/bin/mysql_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

#

extra_args=""

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

then

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

else

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

  then

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

  fi

fi

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

#

# 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

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.

      $bindir/mysqld_safe --datadir="$datadir" --pid-file="$mysqld_pid_file_path" $other_args >/dev/null 2>&1 &

      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

    ;;

  'stop')

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

    # root password.

    if test -s "$mysqld_pid_file_path"

    then

      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

    ;;

  '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

    ;;

  '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

    ;;

  '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`

      # 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

    ;;

    *)

      # usage

      basename=`basename "$0"`

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

      exit 1

    ;;

esac

exit 0

首先，定义相关参数

basedir=

datadir=

# 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

service_startup_timeout=

# Lock directory for RedHat / SuSE.

lockdir='/var/lock/subsys'

lock_file_path="$lockdir/mysql"

其中，

basedir 指的二进制压缩包解压后所在的目录，譬如/usr/local/mysql。

datadir 指的是数据目录

service_startup_timeout=900 定义mysql服务启动的时间限制，如果在900s中没有启动成功，则该脚本会退出。

lockdir='/var/lock/subsys'

关于/var/lock/subsys，网上的解释如下，后续会用到。

总的来说，系统关闭的过程（发出关闭信号，调用服务自身的进程）中会检查/var/lock/subsys下的文件，逐一关闭每个服务，如果某一运行的服务在/var/lock/subsys下没有相应的选项。在系统关闭的时候，会像杀死普通进程一样杀死这个服务。

通过察看/etc/rc.d/init.d下的脚本，可以发现每个服务自己操纵时都会去查看/var/lock/subsys下相应的服务。

很多程序需要判断是否当前已经有一个实例在运行，这个目录就是让程序判断是否有实例运行的标志，比如说xinetd，如果存在这个文件，表示已经有xinetd在运行了，否则就是没有，当然程序里面还要有相应的判断措施来真正确定是否有实例在运行。通常与该目录配套的还有/var/run目录，用来存放对应实例的PID，如果你写脚本的话，会发现这2个目录结合起来可以很方便的判断出许多服务是否在运行，运行的相关信息等等。

判断basedir和datadir

# Set some defaults

mysqld_pid_file_path=

if test -z "$basedir"

then

  basedir=/usr/local/mysql

  bindir=/usr/local/mysql/bin

  if test -z "$datadir"

  then

    datadir=/usr/local/mysql/data

  fi

  sbindir=/usr/local/mysql/bin

  libexecdir=/usr/local/mysql/bin

else

  bindir="$basedir/bin"

  if test -z "$datadir"

  then

    datadir="$basedir/data"

  fi

  sbindir="$basedir/sbin"

  libexecdir="$basedir/libexec"

fi

其中，

mysqld_pid_file_path 指定pid文件的路径

-z string 判断字符串是否为空

如果basedir没有显示设置，则默认为/usr/local/mysql，这也是为什么很多mysql安装教程都推荐将mysql相关文件放到/usr/local/mysql下。

如果datadir没有显示设置，则默认为$basedir/data。

定义log_success_msg()和log_failure_msg()函数

首先，判断/lib/lsb/init-functions文件是否存在，如果存在，则使定义在init-functions文件中的所有shell函数在当前脚本中生效。

如果没有，则定义两个函数，一个用于打印成功日志，一个是打印错误日志。

在RHCS 6.7中，该文件并不存在，已被/etc/init.d/functions所替代。

#

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

#

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

传递参数

将第一个参数传递给mode，剩下的参数传递给other_args

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

export PATH

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

解析配置文件中的参数

这个函数在脚本后面会涉及到。

主要涉及如下参数：--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

}

判断my_print_defaults的位置

首先，它判断当前路径下的bin目录中是否存在该可执行文件，如果不存在，则再判断$bindir（通常指的是$basedir/bin）目录下是否存在。

如果还是没有，则会判断/etc/my.cnf是否存在并且可读，如果是，则判断该配置文件中是否指定了basedir参数，

如果指定了，则取出该参数的值，并判断该值对应的目录中是否存在bin/my_print_defaults可执行文件

最后一步，如果在上述目录中实在没发现my_print_defaults文件，

索性就将print_defaults设置为"my_print_defaults"，寄希望于该命令在当前的PATH环境中。

# Get arguments from the my.cnf file,

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

if test -x ./bin/my_print_defaults

then

  print_defaults="./bin/my_print_defaults"

elif test -x $bindir/my_print_defaults

then

  print_defaults="$bindir/my_print_defaults"

elif test -x $bindir/mysql_print_defaults

then

  print_defaults="$bindir/mysql_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

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

      then

        print_defaults="$d/bin/mysql_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

查找默认的配置文件

-r file 如果文件可读，则为真

#

# 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

#

extra_args=""

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

then

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

else

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

  then

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

  fi

fi

解析配置文件中的参数

my_print_defaults的用法如下：

my_print_defaults --defaults-file=example.cnf client mysql

即读取配置文件中，client和mysql部分的参数配置，

具体在本脚本中，是读取mysqld，server，mysql_server，mysql.server四个部分的配置参数。

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

设置pid file的路径

-z string 判断字符串是否为空

如果--pid-file没有在读取到的配置文件中设置或者脚本刚开始的mysqld_pid_file_path参数没有设置，

则pid file默认设置在datadir下，以主机名.pid命名。

如果该参数设置了，还需要进一步判断

如果该参数中带有斜杠，则代表给定的值带有路径，可直接使用。

如果该参数中没带路径，则代表给定的值只是pid的文件名，可将其设在datadir下。

#

# 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

服务脚本start选项

首先，切换到$basedir中

其次，判断$basedir/bin中的mysqld_safe是否是可执行文件，如果是，则启动mysqld实例，如果不是，则报错退出。

那么，启动流程又是如何实现的呢？

首先，执行$bindir/mysqld_safe --datadir="$datadir" --pid-file="$mysqld_pid_file_path" $other_args >/dev/null 2>&1 &命令，启动mysqld实例。

注意到没有，mysqld_safe其实是在basedir中执行的，包括mysql初始化脚本mysql_install_db，也建议在basedir中执行，具体可参考：

分析MariaDB初始化脚本mysql_install_db

然后通过wait_for_pid函数进行判断，具体可见下文对于wait_for_pid函数的分析

判断完毕后，

查看$lockdir目录是否可写，可写的话，则在目录上创建一个文件。

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.

      $bindir/mysqld_safe --datadir="$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

    ;;

wait_for_pid函数

在利用mysqld_safe启动mysql实例后，会调用该参数

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

其中$!在shell中用于获取最后运行的后台Process的PID，具体在本例中，是mysqld_safe进程的pid。

因为第一个参数是created，所以会执行test -s "$pid_file_path" && i='' && break命令。

-s file 如果文件的长度不为零，则为真

该命令的意思是如果pid文件存在，则将变量i设置为空，并退出while循环。

然后执行如下判断，

  if test -z "$i" ; then

    log_success_msg

    return

  else

    log_failure_msg

    return

  fi

如果$i为空，则打印成功日志，并退出脚本，很显然，在pid文件存在的情况下，会将变量i设置为空。

再来看看pid文件不存在的情况

首先，会判断$pid是否不为空（即if test -n "$pid"）

如果不为空，则代表在执行完mysqld_safe后，已经捕捉到了该进程的pid。

在这种情况下，进一步通过kill -0 "$pid"确认该进程是否存在。

kill -0就是不发送任何信号,但是系统会进行错误检查,所以经常用来检查一个进程是否存在,当进程不存在时, kill -0 pid会返回错误

如果该进程存在，则不执行任何操作，直接跳到如下操作

echo $echo_n ".$echo_c"

i=`expr $i + `

sleep

将变量i加1，并sleep 1s。

然后，继续while循环，之所以这样做，是考虑到mysqld_safe已经执行，但是mysqld实例还在启动过程中，还没创建好pid文件。

一直到$1达到$service_startup_timeout定义的时长。

如果在while循环的过程中，通过kill -0 "$pid"判断到进程已经不存在了，

则会再判断一次，如果这次判断的结果依旧是pid file不存在，且进程不存在，则会执行

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

这就是大名鼎鼎的“The server quit without updating PID file”的由来。

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

}

服务脚本stop选项

首先，判断pid文件的长度是否不为零。

-s file 如果文件的长度不为零，则为真

此时，会通过pid文件获取mysqld进程的pid，注意，不是mysqld_safe进程的pid

然后，判断mysqld进程是否在正常运行，

如果是，则通过kill $mysqld_pid的方式来关闭mysqld进程

杀死进程最安全的方法是单纯使用kill命令，不加修饰符，不带标志。

标准的kill命令通常会终止有问题的进程，并把进程的资源释放给系统。然而，如果进程启动了子进程，只杀死父进程，子进程仍在运行，因此仍消耗资源。为了防止这些所谓的“僵尸进程”，应确保在杀死父进程之前，先杀死其所有的子进程。

然后，调用wait_for_pid函数进行判断，其实，wait_for_pid函数中设置avoid_race_condition变量的目的是为了stop选项，确实有可能出现，mysqld是在检查pid file之后，检查进程是否存活之前退出的。

如果mysqld进程没有正常运行，在会打印“MySQL server process #$mysqld_pid is not running!”信息，并删除pid文件。

如果在执行stop的时候，判断pid文件的长度为0，则会打印"MySQL server PID file could not be found!"信息。

所以，在pid文件不存在的情况下，通过服务脚本执行stop选项并不会关闭mysqld进程，这个时候，就可通过kill $mysqld_pid的方式来关闭mysqld进程。

 'stop')

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

    # root password.

    if test -s "$mysqld_pid_file_path"

    then

      mysqld_pid=`cat "$mysqld_pid_file_path"`

      if (kill - $mysqld_pid >/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

    ;;

服务脚本restart选项

首先，先执行stop操作，如果stop操作成功的话，则继续执行start操作。

如果stop操作失败的话，则会输出"Failed to stop running server, so refusing to try to start."信息，并退出脚本。

  'restart')

    # Stop the service and regardless of whether it was

    # running or not, start it again.

    if $ stop  $other_args; then

      $ start $other_args

    else

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

      exit

    fi

    ;;

服务脚本reload选项

首先，判断pid文件的长度是否为0，如果不为0，则将该文件中的值设置为mysqld_pid变量的值。

然后对该进程执行kill -HUP操作。

kill -HUP pid 

pid 是进程标识。如果想要更改配置而不需停止并重新启动服务，请使用该命令。在对配置文件作必要的更改后，发出该命令以动态更新服务配置。

根据约定，当您发送一个挂起信号（信号  或 HUP）时，大多数服务器进程（所有常用的进程）都会进行复位操作并重新加载它们的配置文件。

如果pid文件的长度为0，则输出"MySQL PID file could not be found!"。

  '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

    fi

    ;;

服务脚本status选项

首先，判断pid文件长度是否为0，如果不是，则读取该文件中的值，并判断pid对应的进程是否运行正常，

如果运行正常，则输出"MySQL running"

如果不正常，则输出"MySQL is not running, but PID file exists"

如果pid文件的长度为0，则试图通过mysqld的启动命令来获取其pid，

这个时候，可能存在一个mysqld程序启动了多个实例，这会导致pid_count=`echo $mysqld_pid | wc -w`大于1。

这个时候，会输出"Multiple MySQL running but PID file could not be found"信息，并退出脚本。

如果mysqld_pid为空，则会继续判断"$lock_file_path"是否存在，如果存在，

则会输出"MySQL is not running, but lock file ($lock_file_path) exists"信息。

如果"$lock_file_path"不存在，则会输出"MySQL is not running"信息。

如果mysqld_pid等于1，则会输出"MySQL is running but PID file could not be found"信息。

  '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 - $mysqld_pid >/dev/null ; then

        log_success_msg "MySQL running ($mysqld_pid)"

        exit

      else

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

        exit

      fi

    else

      # Try to find appropriate mysqld process

      mysqld_pid=`pidof $libexecdir/mysqld`

      # test if multiple pids exist

      pid_count=`echo $mysqld_pid | wc -w`

      if test $pid_count -gt  ; then

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

        exit

      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

        fi

        log_failure_msg "MySQL is not running"

        exit

      else

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

        exit

      fi

    fi

    ;;

服务脚本其它选项

如果脚本的第一个参数不是上述几个选项，则会输出Usage信息。

    *)

      # usage

      basename=`basename "$0"`

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

      exit

    ;;

至此，mysql的服务脚本分析完毕~

总结

在通过服务脚本启动mysql的过程中，报“The server quit without updating PID file”错误，有两个条件

首先，pid文件不存在

其次，通过kill -0 $pid检查到进程并不存在

这个时候，只能通过mysql数据库的错误日志来定位。

服务脚本如果不做任何调整的话，默认的basedir是/usr/local/mysql，datadir是/usr/local/mysql/data

如果自己的mysql服务不是默认路径，

则需要在该脚本中显式设置

经测试，需设置如下几处：

1. 设置basedir和添加conf变量

其中，conf指的是mysqld的配置文件，建议配置文件中显式指定basedir和datadir的值。

在这里，datadir可不设置，因为datadir可通过配置文件来获取。

但是basedir必须要指定，因为要首先根据basedir来判断my_print_deefauts命令

basedir=/usr/local/mysql-advanced-5.6.-linux-glibc2.-x86_64

datadir=

conf=/usr/local/mysql-advanced-5.6.-linux-glibc2.-x86_64/my_3308.cnf

2. 第256行，添加extra_args=" -c $conf"

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

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

then

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

else

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

  then

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

  fi

fi

extra_args=" -c $conf"

3. 修改285行mysqld_safe的启动参数

将

      $bindir/mysqld_safe --datadir="$datadir" --pid-file="$mysqld_pid_file_path" $other_args >/dev/null >& &

修改为，

      $bindir/mysqld_safe --defaults-file="$conf" --datadir="$datadir" --pid-file="$mysqld_pid_file_path" $other_args >/dev/null >&1 &

主要是添加了--defaults-file选项

参考

1. shell中test命令用法详解

2. shell中$0,$?,$!等的特殊用法

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