本文主要介紹了MySQL啟動時報“The server quit without updating PID file”錯誤的原因,需要的朋友可以參考下，希望能幫助到大家。

很多童鞋在啟動mysql的時候，碰到過這個錯誤，

首先，澄清一點，出現(xiàn)這個錯誤的前提是：通過服務腳本來啟動mysql。通過mysqld_safe或mysqld啟動mysql實例并不會報這個錯誤。

那么，出現(xiàn)這個錯誤的原因具體是什么呢？

哈哈，對分析過程不care的童鞋可直接跳到文末的總結部分~

總結

下面，來分析下mysql的服務啟動腳本

腳本完整內(nèi)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

首先，定義相關參數(shù)

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 指的二進制壓縮包解壓后所在的目錄，譬如/usr/local/mysql。

datadir 指的是數(shù)據(jù)目錄

service_startup_timeout=900 定義mysql服務啟動的時間限制，如果在900s中沒有啟動成功，則該腳本會退出。

lockdir='/var/lock/subsys'

關于/var/lock/subsys，網(wǎng)上的解釋如下，后續(xù)會用到。

總的來說，系統(tǒng)關閉的過程（發(fā)出關閉信號，調用服務自身的進程）中會檢查/var/lock/subsys下的文件，逐一關閉每個服務，如果某一運行的服務在/var/lock/subsys下沒有相應的選項。在系統(tǒng)關閉的時候，會像殺死普通進程一樣殺死這個服務。

通過察看/etc/rc.d/init.d下的腳本，可以發(fā)現(xiàn)每個服務自己操縱時都會去查看/var/lock/subsys下相應的服務。

很多程序需要判斷是否當前已經(jīng)有一個實例在運行，這個目錄就是讓程序判斷是否有實例運行的標志，比如說xinetd，如果存在這個文件，表示已經(jīng)有xinetd在運行了，否則就是沒有，當然程序里面還要有相應的判斷措施來真正確定是否有實例在運行。通常與該目錄配套的還有/var/run目錄，用來存放對應實例的PID，如果你寫腳本的話，會發(fā)現(xiàn)這2個目錄結合起來可以很方便的判斷出許多服務是否在運行，運行的相關信息等等。

判斷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文件的路徑

-z string 判斷字符串是否為空

如果basedir沒有顯示設置，則默認為/usr/local/mysql，這也是為什么很多mysql安裝教程都推薦將mysql相關文件放到/usr/local/mysql下。

如果datadir沒有顯示設置，則默認為$basedir/data。

定義log_success_msg()和log_failure_msg()函數(shù)

首先，判斷/lib/lsb/init-functions文件是否存在，如果存在，則使定義在init-functions文件中的所有shell函數(shù)在當前腳本中生效。

如果沒有，則定義兩個函數(shù)，一個用于打印成功日志，一個是打印錯誤日志。

在RHCS 6.7中，該文件并不存在，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

傳遞參數(shù)

將第一個參數(shù)傳遞給mode，剩下的參數(shù)傳遞給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

解析配置文件中的參數(shù)

這個函數(shù)在腳本后面會涉及到。

主要涉及如下參數(shù)：--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
}

判斷my_print_defaults的位置

首先，它判斷當前路徑下的bin目錄中是否存在該可執(zhí)行文件，如果不存在，則再判斷$bindir（通常指的是$basedir/bin）目錄下是否存在。

如果還是沒有，則會判斷/etc/my.cnf是否存在并且可讀，如果是，則判斷該配置文件中是否指定了basedir參數(shù)，

如果指定了，則取出該參數(shù)的值，并判斷該值對應的目錄中是否存在bin/my_print_defaults可執(zhí)行文件

最后一步，如果在上述目錄中實在沒發(fā)現(xiàn)my_print_defaults文件，

索性就將print_defaults設置為"my_print_defaults"，寄希望于該命令在當前的PATH環(huán)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

查找默認的配置文件

-r file 如果文件可讀，則為真

#
# 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

解析配置文件中的參數(shù)

my_print_defaults的用法如下：

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

即讀取配置文件中，client和mysql部分的參數(shù)配置，

具體在本腳本中，是讀取mysqld，server，mysql_server，mysql.server四個部分的配置參數(shù)。

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

設置pid file的路徑

-z string 判斷字符串是否為空

如果--pid-file沒有在讀取到的配置文件中設置或者腳本剛開始的mysqld_pid_file_path參數(shù)沒有設置，

則pid file默認設置在datadir下，以主機名.pid命名。

如果該參數(shù)設置了，還需要進一步判斷

如果該參數(shù)中帶有斜杠，則代表給定的值帶有路徑，可直接使用。

如果該參數(shù)中沒帶路徑，則代表給定的值只是pid的文件名，可將其設在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

服務腳本start選項

首先，切換到$basedir中

其次，判斷$basedir/bin中的mysqld_safe是否是可執(zhí)行文件，如果是，則啟動mysqld實例，如果不是，則報錯退出。

那么，啟動流程又是如何實現(xiàn)的呢？

首先，執(zhí)行$bindir/mysqld_safe --datadir="$datadir" --pid-file="$mysqld_pid_file_path" $other_args >/dev/null 2>&1 &命令，啟動mysqld實例。

注意到?jīng)]有，mysqld_safe其實是在basedir中執(zhí)行的，包括mysql初始化腳本mysql_install_db，也建議在basedir中執(zhí)行，具體可參考：

分析MariaDB初始化腳本mysql_install_db

然后通過wait_for_pid函數(shù)進行判斷，具體可見下文對于wait_for_pid函數(shù)的分析

判斷完畢后，

查看$lockdir目錄是否可寫，可寫的話，則在目錄上創(chuàng)建一個文件。

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函數(shù)

在利用mysqld_safe啟動mysql實例后，會調用該參數(shù)

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

其中$!在shell中用于獲取最后運行的后臺Process的PID，具體在本例中，是mysqld_safe進程的pid。

因為第一個參數(shù)是created，所以會執(zhí)行test -s "$pid_file_path" && i='' && break命令。

-s file 如果文件的長度不為零，則為真

該命令的意思是如果pid文件存在，則將變量i設置為空，并退出while循環(huán)。

然后執(zhí)行如下判斷，

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

如果$i為空，則打印成功日志，并退出腳本，很顯然，在pid文件存在的情況下，會將變量i設置為空。

再來看看pid文件不存在的情況

首先，會判斷$pid是否不為空（即if test -n "$pid"）

如果不為空，則代表在執(zhí)行完mysqld_safe后，已經(jīng)捕捉到了該進程的pid。

在這種情況下，進一步通過kill -0 "$pid"確認該進程是否存在。

kill -0就是不發(fā)送任何信號,但是系統(tǒng)會進行錯誤檢查,所以經(jīng)常用來檢查一個進程是否存在,當進程不存在時, kill -0 pid會返回錯誤

如果該進程存在，則不執(zhí)行任何操作，直接跳到如下操作

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

將變量i加1，并sleep 1s。

然后，繼續(xù)while循環(huán)，之所以這樣做，是考慮到mysqld_safe已經(jīng)執(zhí)行，但是mysqld實例還在啟動過程中，還沒創(chuàng)建好pid文件。

一直到$1達到$service_startup_timeout定義的時長。

如果在while循環(huán)的過程中，通過kill -0 "$pid"判斷到進程已經(jīng)不存在了，

則會再判斷一次，如果這次判斷的結果依舊是pid file不存在，且進程不存在，則會執(zhí)行

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

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

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
}

服務腳本stop選項

首先，判斷pid文件的長度是否不為零。

-s file 如果文件的長度不為零，則為真

此時，會通過pid文件獲取mysqld進程的pid，注意，不是mysqld_safe進程的pid

然后，判斷mysqld進程是否在正常運行，

如果是，則通過kill $mysqld_pid的方式來關閉mysqld進程

殺死進程最安全的方法是單純使用kill命令，不加修飾符，不帶標志。

標準的kill命令通常會終止有問題的進程，并把進程的資源釋放給系統(tǒng)。然而，如果進程啟動了子進程，只殺死父進程，子進程仍在運行，因此仍消耗資源。為了防止這些所謂的“僵尸進程”，應確保在殺死父進程之前，先殺死其所有的子進程。

然后，調用wait_for_pid函數(shù)進行判斷，其實，wait_for_pid函數(shù)中設置avoid_race_condition變量的目的是為了stop選項，確實有可能出現(xiàn)，mysqld是在檢查pid file之后，檢查進程是否存活之前退出的。

如果mysqld進程沒有正常運行，在會打印“MySQL server process #$mysqld_pid is not running!”信息，并刪除pid文件。

如果在執(zhí)行stop的時候，判斷pid文件的長度為0，則會打印"MySQL server PID file could not be found!"信息。

所以，在pid文件不存在的情況下，通過服務腳本執(zhí)行stop選項并不會關閉mysqld進程，這個時候，就可通過kill $mysqld_pid的方式來關閉mysqld進程。

'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
 ;;

服務腳本restart選項

首先，先執(zhí)行stop操作，如果stop操作成功的話，則繼續(xù)執(zhí)行start操作。

如果stop操作失敗的話，則會輸出"Failed to stop running server, so refusing to try to start."信息，并退出腳本。

 '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
 ;;

服務腳本reload選項

首先，判斷pid文件的長度是否為0，如果不為0，則將該文件中的值設置為mysqld_pid變量的值。

然后對該進程執(zhí)行kill -HUP操作。

kill -HUP pid

pid 是進程標識。如果想要更改配置而不需停止并重新啟動服務，請使用該命令。在對配置文件作必要的更改后，發(fā)出該命令以動態(tài)更新服務配置。

根據(jù)約定，當您發(fā)送一個掛起信號（信號 1 或 HUP）時，大多數(shù)服務器進程（所有常用的進程）都會進行復位操作并重新加載它們的配置文件。

如果pid文件的長度為0，則輸出"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
 ;;

服務腳本status選項

首先，判斷pid文件長度是否為0，如果不是，則讀取該文件中的值，并判斷pid對應的進程是否運行正常，

如果運行正常，則輸出"MySQL running"

如果不正常，則輸出"MySQL is not running, but PID file exists"

如果pid文件的長度為0，則試圖通過mysqld的啟動命令來獲取其pid，

這個時候，可能存在一個mysqld程序啟動了多個實例，這會導致pid_count=`echo $mysqld_pid wc -w`大于1。

這個時候，會輸出"Multiple MySQL running but PID file could not be found"信息，并退出腳本。

如果mysqld_pid為空，則會繼續(xù)判斷"$lock_file_path"是否存在，如果存在，

則會輸出"MySQL is not running, but lock file ($lock_file_path) exists"信息。

如果"$lock_file_path"不存在，則會輸出"MySQL is not running"信息。

如果mysqld_pid等于1，則會輸出"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
 ;;

服務腳本其它選項

如果腳本的第一個參數(shù)不是上述幾個選項，則會輸出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的服務腳本分析完畢~

總結

在通過服務腳本啟動mysql的過程中，報“The server quit without updating PID file”錯誤，有兩個條件

首先，pid文件不存在

其次，通過kill -0 $pid檢查到進程并不存在

這個時候，只能通過mysql數(shù)據(jù)庫的錯誤日志來定位。

服務腳本如果不做任何調整的話，默認的basedir是/usr/local/mysql，datadir是/usr/local/mysql/data

如果自己的mysql服務均不是默認路徑，

則需要在該腳本中顯式設置

經(jīng)測試，需設置如下幾處：

1. 設置basedir和添加conf變量

其中，conf指的是mysqld的配置文件，建議配置文件中顯式指定basedir和datadir的值。

在這里，datadir可不設置，因為datadir可通過配置文件來獲取。

但是basedir必須要指定，因為要首先根據(jù)basedir來判斷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的啟動參數(shù)

將

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

修改為，

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

主要是添加了--defaults-file選項

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