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    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

    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服务均不是默认路径,

    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

    以上所述是小编给大家介绍的深度解析MySQL启动时报“The server quit without updating PID file”错误的原因,希望对大家有所帮助,如果大家有任何疑问请给我留言,小编会及时回复大家的。在此也非常感谢大家对脚本之家网站的支持!

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