/etc/init.d/rc文件语法解析

#! /bin/sh

PATH=/sbin:/usr/sbin:/bin:/usr/bin #设置环境变量
export PATH

CONCURRENCY=makefile 

scriptname="$0" #$0表示传入的第一个参数，如执行 ./rc 1 2 第一个参数是./rc,第二个是1。

umask 022 #设置当前目录默认文件权限

on_exit() { #函数
	echo "error: '$scriptname' exited outside the expected code flow."
}
trap on_exit EXIT #若遇到EXIT信号则执行on_exit()函数

trap ":" INT QUIT TSTP #若遇到INT等信号则执行空语句(冒号表示空语句)

stty onlcr 0>&1 #设置终端命令行，标准输入重定向到标准输出（0:标准输入;1:标准输出;2:标准错误输出）

if [ -e /lib/init/splash-functions-base ] ; then #若存在xx文件
	. /lib/init/splash-functions-base #执行脚本（可以理解为执行脚本./splash-functions-base类似语法结构）
else
	splash_progress() { return 1; } #
	splash_stop() { return 1; } #
fi 

runlevel=$RUNLEVEL

[ "$1" != "" ] && runlevel=$1 #若有第2个参数，则赋值给变量runlevel(运行级别)
if [ "$runlevel" = "" ]
then
	echo "Usage: $scriptname <runlevel>" >&2 #标准输出重定向到标准错误输出
	exit 1
fi
previous=$PREVLEVEL
[ "$previous" = "" ] && previous=N

export runlevel previous #设置为环境变量(当前shell有效)

if [ -f /etc/default/rcS ] ; then #是普通文件则运行(非目录、设备文件等)
	. /etc/default/rcS
fi
export VERBOSE

if [ -f /lib/lsb/init-functions ] ; then #是普通文件则运行(非目录、设备文件等)
	. /lib/lsb/init-functions
else
	log_action_msg() { echo $@; } #$@显示所有向此脚本传递的参数
	log_failure_msg() { echo $@; }
	log_warning_msg() { echo $@; }
fi

startup_progress() {

	if [ 0 -eq "$num_steps" ] ; then return; fi

	step=$(($step + $step_change))
	progress=$(($step * $progress_size / $num_steps + $first_step))
	$debug splash_progress "$progress" || true
}


if [ "none" != "$CONCURRENCY" ] ; then
	test -s /etc/init.d/.depend.boot  || CONCURRENCY="none"
	test -s /etc/init.d/.depend.start || CONCURRENCY="none"
	test -s /etc/init.d/.depend.stop  || CONCURRENCY="none"
	if test -e /etc/init.d/.legacy-bootordering ; then
		CONCURRENCY="none"
	fi
	startpar -v > /dev/null 2>&1 || CONCURRENCY="none"
fi

case "$CONCURRENCY" in
	makefile|startpar|shell) # startpar and shell are obsolete
		CONCURRENCY=makefile
		log_action_msg "Using makefile-style concurrent boot in runlevel $runlevel"

		startup() {
			if [ start = "$1" ] || [ boot = "$1" ]
			then
				$debug splash_stop || true
			fi
			eval "$(startpar -p 4 -t 20 -T 3 -M $1 -P $previous -R $runlevel)"

			if [ -n "$failed_service" ]
			then
				log_failure_msg "startpar: service(s) returned failure: $failed_service"
			fi

			if [ -n "$skipped_service" ]
			then
				log_warning_msg "startpar: service(s) skipped: $skipped_service"
			fi

			unset failed_service skipped_service
		}
		;;
	none|*)
		startup() {
			action=$1
			shift
			scripts="$@"
			for script in $scripts ; do
				$debug "$script" $action
				startup_progress
			done
		}
		;;
esac

is_splash_stop_scripts() {
	scriptname=$1
	case "$scriptname" in
		# killprocs is used in runlevel 1
		gdm|xdm|kdm|ltsp-client|ltsp-client-core|reboot|halt|killprocs)
			return 0
			;;
	esac
	return 1
}

if [ -d /etc/rc$runlevel.d ]
then

	PROGRESS_STATE=0
	if [ -f /dev/.initramfs/progress_state ]; then
		. /dev/.initramfs/progress_state
	fi

	progress_size=$(((100 - $PROGRESS_STATE) / 3))

	case "$runlevel" in
		0|6)
			ACTION=stop

			first_step=0
			progress_size=100
			step_change=-1
			;;
		S)
			ACTION=start

			first_step=$PROGRESS_STATE
			progress_size=$(($progress_size * 2))
			step_change=1
			;;
		*)
			ACTION=start

			first_step=$(($progress_size * 2 + $PROGRESS_STATE))
			step_change=1
			;;
	esac

	num_steps=0
	for s in /etc/rc$runlevel.d/[SK]*; do
		if is_splash_stop_scripts "${s##/etc/rc$runlevel.d/S??}" ; then
			break
		fi
		num_steps=$(($num_steps + 1))
	done
	step=0

	if [ makefile = "$CONCURRENCY" ]
	then
		if [ "$ACTION" = "start" ] && [ "$previous" != N ]
		then
			startup stop
		fi
	elif [ "$previous" != N ]
	then
		# Run all scripts with the same level in parallel
		CURLEVEL=""
		for s in /etc/rc$runlevel.d/K*
		do
			# Extract order value from symlink
			level=${s#/etc/rc$runlevel.d/K}
			level=${level%%[a-zA-Z]*}
			if [ "$level" = "$CURLEVEL" ]
			then
				continue
			fi
			CURLEVEL=$level
			SCRIPTS=""
			for i in /etc/rc$runlevel.d/K$level*
			do
				# Check if the script is there.
				[ ! -f $i ] && continue

				#
				# Find stop script in previous runlevel but
				# no start script there.
				#
				suffix=${i#/etc/rc$runlevel.d/K[0-9][0-9]}
				previous_stop=/etc/rc$previous.d/K[0-9][0-9]$suffix
				previous_start=/etc/rc$previous.d/S[0-9][0-9]$suffix
				#
				# If there is a stop script in the previous level
				# and _no_ start script there, we don't
				# have to re-stop the service.
				#
				[ -f $previous_stop ] && [ ! -f $previous_start ] && continue

				# Stop the service.
				SCRIPTS="$SCRIPTS $i"
				if is_splash_stop_scripts "$suffix" ; then
					$debug splash_stop || true
				fi
			done
			startup stop $SCRIPTS
		done
	fi

	if [ makefile = "$CONCURRENCY" ]
	then
		if [ S = "$runlevel" ]
		then
			startup boot
		else
			startup $ACTION
		fi
	else
		# Now run the START scripts for this runlevel.
		# Run all scripts with the same level in parallel
		CURLEVEL=""
		for s in /etc/rc$runlevel.d/S*
		do
			# Extract order value from symlink
			level=${s#/etc/rc$runlevel.d/S}
			level=${level%%[a-zA-Z]*}
			if [ "$level" = "$CURLEVEL" ]
			then
				continue
			fi
			CURLEVEL=$level
			SCRIPTS=""
			for i in /etc/rc$runlevel.d/S$level*
			do
				[ ! -f $i ] && continue

				suffix=${i#/etc/rc$runlevel.d/S[0-9][0-9]}
				if [ "$previous" != N ]
				then
					#
					# Find start script in previous runlevel and
					# stop script in this runlevel.
					#
					stop=/etc/rc$runlevel.d/K[0-9][0-9]$suffix
					previous_start=/etc/rc$previous.d/S[0-9][0-9]$suffix
					#
					# If there is a start script in the previous level
					# and _no_ stop script in this level, we don't
					# have to re-start the service.
					#
					if [ start = "$ACTION" ] ; then
						[ -f $previous_start ] && [ ! -f $stop ] && continue
					else
						# Workaround for the special
						# handling of runlevels 0 and 6.
						previous_stop=/etc/rc$previous.d/K[0-9][0-9]$suffix
						#
						# If there is a stop script in the previous level
						# and _no_ start script there, we don't
						# have to re-stop the service.
						#
						[ -f $previous_stop ] && [ ! -f $previous_start ] && continue
					fi

				fi
				SCRIPTS="$SCRIPTS $i"
				if is_splash_stop_scripts "$suffix" ; then
					$debug splash_stop || true
				fi
			done
			startup $ACTION $SCRIPTS
		done
	fi
fi

trap - EXIT # Disable emergency handler

exit 0