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

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 1996 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: 2345 64 36
# 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:  2 3 4 5
# Default-Stop: 0 1 6
# 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. 
# 0 means don't wait at all
# Negative numbers mean to wait indefinitely
service_startup_timeout=900

# 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=$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 "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=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
}

# 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
View Code

 

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. 
# 0 means don't wait at all
# Negative numbers mean to wait indefinitely
service_startup_timeout=900

# 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=$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 "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=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
}

 

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" $other_args >/dev/null 2>&1 &
      wait_for_pid created "$!" "$mysqld_pid_file_path"; return_value=$?

      # 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
    ;;

 

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 0
  else
    log_failure_msg
    return 1
  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 + 1`
sleep 1

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=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
}

 

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 -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
    ;;

 

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 $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
    ;;

 

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 1 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 1
    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 -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
    ;;

 

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 1
    ;;

 

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-5.6.23-linux-glibc2.5-x86_64
datadir=
conf=/usr/local/mysql-advanced-5.6.23-linux-glibc2.5-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

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

修改为,

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

posted @ 2017-05-17 15:19 iVictor 阅读(...) 评论(...) 编辑 收藏