mysql启动脚本详解

  1 #!/bin/sh

  2 # Copyright Abandoned 1996 TCX DataKonsult AB & Monty Program KB & Detron HB

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

  4 

  5 # MySQL daemon start/stop script.

  6 

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

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

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

 10 # started and shut down when the systems goes down.

 11 

 12 # Comments to support chkconfig on RedHat Linux

 13 # chkconfig: 2345 64 36

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

 15 

 16 # Comments to support LSB init script conventions

 17 ### BEGIN INIT INFO

 18 # Provides: mysql

 19 # Required-Start: $local_fs $network $remote_fs

 20 # Should-Start: ypbind nscd ldap ntpd xntpd

 21 # Required-Stop: $local_fs $network $remote_fs

 22 # Default-Start:  2 3 4 5

 23 # Default-Stop: 0 1 6

 24 # Short-Description: start and stop MySQL

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

 26 ### END INIT INFO

 27  

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

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

 30 #

 31 # - Run this script from within the MySQL installation directory

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

 33 #   [mysqld]

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

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

 36 #   and copy my_print_defaults to /usr/bin

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

 38 #   below.

 39 #

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

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

 42 

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

 44 # overwritten by settings in the MySQL configuration files.

 45 

 46 basedir=            #mysql的安装目录

 47 datadir=            #数据存储路径

 48 

 49 # Default value, in seconds, afterwhich the script should timeout waiting

 50 # for server start. 

 51 # Value here is overriden by value in my.cnf. 

 52 # 0 means don't wait at all

 53 # Negative numbers mean to wait indefinitely

 54 service_startup_timeout=900

 55 

 56 # Lock directory for RedHat / SuSE.

 57 lockdir='/var/lock/subsys'                #mysql进程锁

 58 lock_file_path="$lockdir/mysql"

 59 

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

 61 

 62 # Set some defaults

 63 mysqld_pid_file_path=

 64 if test -z "$basedir"                     #依次确定$basedir,$datadir,$bindir等路径

 65 then

 66   basedir=/usr

 67   bindir=/usr/bin

 68   if test -z "$datadir"   

 69   then

 70     datadir=/var/lib/mysql

 71   fi

 72   sbindir=/usr/sbin

 73   libexecdir=/usr/sbin

 74 else

 75   bindir="$basedir/bin"

 76   if test -z "$datadir"

 77   then

 78     datadir="$basedir/data"

 79   fi

 80   sbindir="$basedir/sbin"

 81   libexecdir="$basedir/libexec"

 82 fi

 83 

 84 # datadir_set is used to determine if datadir was set (and so should be

 85 # *not* set inside of the --basedir= handler.)

 86 datadir_set=

 87 

 88 #

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

 90 #

 91 lsb_functions="/lib/lsb/init-functions"   #linux系统脚本，包含打印log函数

 92 if test -f $lsb_functions ; then    #如果存在改文件，将这些函数导入该脚本

 93   . $lsb_functions

 94 else                              #否则使用自定义信息

 95   log_success_msg()

 96   {

 97     echo " SUCCESS! $@"

 98   }

 99   log_failure_msg()

100   {

101     echo " ERROR! $@"

102   }

103 fi

104 

105 PATH="/sbin:/usr/sbin:/bin:/usr/bin:$basedir/bin"           #添加$basrdir到系统环境变量

106 export PATH

107 

108 mode=$1    # start or Stop        #传入启动脚本的第1个参数

109 

110 [ $# -ge 1 ] && shift      #如果参数个数大于等于1个，shift删掉第一个参数，将剩余参数传给$other_args

111 

112 

113 other_args="$*"   # uncommon, but needed when called from an RPM upgrade action

114            # Expected: "--skip-networking --skip-grant-tables"

115            # They are not checked here, intentionally, as it is the resposibility

116            # of the "spec" file author to give correct arguments only.

117 

118 case `echo "testing\c"`,`echo -n testing`     #echo_c和echo_n的定义；\c不加换行符，-n不换行

119     *c*,-n*) echo_n=   echo_c=     ;;

120     *c*,*)   echo_n=-n echo_c=     ;;

121     *)       echo_n=   echo_c='\c' ;;

122 esac

123 

124 

125 parse_server_arguments() {                 #该函数将my_print_defaults 命令分析出得参数赋值给相应的变量

126   for arg do 

127     case "$arg" in

128       --basedir=*)  basedir=`echo "$arg" | sed -e 's/^[^=]*=//'`    #利用正则表达式获取

129                     bindir="$basedir/bin"

130             if test -z "$datadir_set"; then  

131               datadir="$basedir/data"

132             fi

133             sbindir="$basedir/sbin"

134             libexecdir="$basedir/libexec"

135         ;;

136       --datadir=*)  datadir=`echo "$arg" | sed -e 's/^[^=]*=//'`

137             datadir_set=1

138     ;;

139       --pid-file=*) mysqld_pid_file_path=`echo "$arg" | sed -e 's/^[^=]*=//'` ;;

140       --service-startup-timeout=*) service_startup_timeout=`echo "$arg" | sed -e 's/^[^=]*=//'` ;;

141     esac

142   done

143 }

144 

145 

146 

147 wait_for_pid () {                        #该函数在启动和停止mysql服务时用于等待pid的生成

148   verb="$1"           # created | removed

149   pid="$2"            # process ID of the program operating on the pid-file

150   pid_file_path="$3" # path to the PID file.

151 

152   i=0

153   avoid_race_condition="by checking again"

154 

155   while test $i -ne $service_startup_timeout ; do    

156 

157     case "$verb" in                                  #处理第1个参数，created或removed

158       'created')

159         # wait for a PID-file to pop into existence.

160         test -s "$pid_file_path" && i='' && break

161         ;;

162       'removed')

163         # wait for this PID-file to disappear

164         test ! -s "$pid_file_path" && i='' && break

165         ;;

166       *)

167         echo "wait_for_pid () usage: wait_for_pid created|removed pid pid_file_path"

168         exit 1

169         ;;

170     esac

171 

172     # if server isn't running, then pid-file will never be updated

173     if test -n "$pid"; then                 #如果pid非空

174       if kill -0 "$pid" 2>/dev/null; then   #kill -0发送一个无效信号，可检查进程是否存在，存在返回0，反之则1

175         :  # the server still runs

176       else

177         # The server may have exited between the last pid-file check and now.  

178         if test -n "$avoid_race_condition"; then

179           avoid_race_condition=""

180           continue  # Check again.

181         fi

182 

183         # there's nothing that will affect the file.

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

185         return 1  # not waiting any more.

186       fi

187     fi

188 

189     echo $echo_n ".$echo_c"    

190     i=`expr $i + 1`

191     sleep 1                   #睡眠1秒

192 

193   done

194 

195   if test -z "$i" ; then   #如果i长度为0

196     log_success_msg

197     return 0

198   else

199     log_failure_msg

200     return 1

201   fi

202 }

203 

204 

205 # Get arguments from the my.cnf file,

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

207 if test -x ./bin/my_print_defaults　　　　　　　　　　#找到print_defaults的路径

208 then

209   print_defaults="./bin/my_print_defaults"

210 elif test -x $bindir/my_print_defaults

211 then

212   print_defaults="$bindir/my_print_defaults"

213 elif test -x $bindir/mysql_print_defaults

214 then

215   print_defaults="$bindir/mysql_print_defaults"

216 else

217   # Try to find basedir in /etc/my.cnf

218   conf=/etc/my.cnf

219   print_defaults=

220   if test -r $conf                         #如果可读，从配置文件$conf读取

221   then

222     subpat='^[^=]*basedir[^=]*=\(.*\)$'

223     dirs=`sed -e "/$subpat/!d" -e 's//\1/' $conf`

224     for d in $dirs

225     do

226       d=`echo $d | sed -e 's/[     ]//g'`

227       if test -x "$d/bin/my_print_defaults"

228       then

229         print_defaults="$d/bin/my_print_defaults"

230         break

231       fi

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

233       then

234         print_defaults="$d/bin/mysql_print_defaults"

235         break

236       fi

237     done

238   fi

239 

240   # Hope it's in the PATH ... but I doubt it

241   test -z "$print_defaults" && print_defaults="my_print_defaults"     #还是不行，就用my_print_defaults

242 fi

243 

244 #

245 # Read defaults file from 'basedir'.   If there is no defaults file there

246 # check if it's in the old (depricated) place (datadir) and read it from there

247 #

248 

249 #配置文件的目录，先从basedir读取，不行再读取datadir的

250 extra_args=""

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

252 then

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

254 else

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

256   then

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

258   fi

259 fi

260 

261 #使用parse_server_arguments函数和my_print_defaults 从my.cnf 中获取相应的参数并付给相应的变量

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

263 

264 #

265 # Set pid file if not given

266 #指定mysql启动时进程文件的位置

267 if test -z "$mysqld_pid_file_path"

268 then

269   mysqld_pid_file_path=$datadir/`hostname`.pid

270 else

271   case "$mysqld_pid_file_path" in

272     /* ) ;;

273     * )  mysqld_pid_file_path="$datadir/$mysqld_pid_file_path" ;;

274   esac

275 fi

276 

277 case "$mode" in

278   'start')

279     # Start daemon

280 

281     # Safeguard (relative paths, core dumps..)

282     cd $basedir

283 

284     echo $echo_n "Starting MySQL"

285     if test -x $bindir/mysqld_safe  #如果mysqld_safe存在且可执行

286     then

287       # Give extra arguments to mysqld with the my.cnf file. This script

288       # may be overwritten at next upgrade.

289       #关键语句，启动mysqld_safe，传入3个参数：datadir,pid-file,other_args；将输出丢弃到系统黑洞/dev/null

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

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

292 

293       # Make lock for RedHat / SuSE          ＃mysql锁的检测和创建

294       if test -w "$lockdir"       #如果存在且可写

295       then

296         touch "$lock_file_path"

297       fi

298 

299       exit $return_value

300     else

301       log_failure_msg "Couldn't find MySQL server ($bindir/mysqld_safe)"

302     fi

303     ;;

304 

305   'stop')

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

307     # root password.

308 

309     if test -s "$mysqld_pid_file_path"    #如果非空

310     then

311       mysqld_pid=`cat "$mysqld_pid_file_path"`      ＃获取mysqld进程

312 

313       if (kill -0 $mysqld_pid 2>/dev/null)

314       then

315         echo $echo_n "Shutting down MySQL"

316         kill $mysqld_pid                             ＃杀死

317         # mysqld should remove the pid file when it exits, so wait for it.

318         wait_for_pid removed "$mysqld_pid" "$mysqld_pid_file_path"; return_value=$?

319       else

320         log_failure_msg "MySQL server process #$mysqld_pid is not running!"

321         rm "$mysqld_pid_file_path"

322       fi

323 

324       # Delete lock for RedHat / SuSE

325       if test -f "$lock_file_path"    #如果存在锁，需要移除

326       then

327         rm -f "$lock_file_path"

328       fi

329       exit $return_value

330     else

331       log_failure_msg "MySQL server PID file could not be found!"

332     fi

333     ;;

334 

335   'restart')                    

336     # Stop the service and regardless of whether it was          #重启mysql

337     # running or not, start it again.

338     if $0 stop  $other_args; then

339       $0 start $other_args

340     else

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

342       exit 1

343     fi

344     ;;

345 

346   'reload'|'force-reload')                        #重载mysql

347     if test -s "$mysqld_pid_file_path" ; then

348       read mysqld_pid <  "$mysqld_pid_file_path"

349       kill -HUP $mysqld_pid && log_success_msg "Reloading service MySQL"

350       touch "$mysqld_pid_file_path"

351     else

352       log_failure_msg "MySQL PID file could not be found!"

353       exit 1

354     fi

355     ;;

356   'status')               

357     # First, check to see if pid file exists           #mysql的状态           

358     if test -s "$mysqld_pid_file_path" ; then 

359       read mysqld_pid < "$mysqld_pid_file_path"

360       if kill -0 $mysqld_pid 2>/dev/null ; then 

361         log_success_msg "MySQL running ($mysqld_pid)"

362         exit 0

363       else

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

365         exit 1

366       fi

367     else

368       # Try to find appropriate mysqld process                             

369       mysqld_pid=`pidof $libexecdir/mysqld`

370 

371       # test if multiple pids exist

372       pid_count=`echo $mysqld_pid | wc -w`

373       if test $pid_count -gt 1 ; then

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

375         exit 5

376       elif test -z $mysqld_pid ; then 

377         if test -f "$lock_file_path" ; then 

378           log_failure_msg "MySQL is not running, but lock file ($lock_file_path) exists"

379           exit 2

380         fi 

381         log_failure_msg "MySQL is not running"

382         exit 3

383       else

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

385         exit 4

386       fi

387     fi

388     ;;

389     *)

390       # usage            #输出用法的提示

391       basename=`basename "$0"`

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

393       exit 1

394     ;;

395 esac

396 

397 exit 0