用于管理Linux系统中的各种服务的命令service命令

我们知道service命令是用于管理Linux系统中的各种服务的命令。其实service是位于系统中/usr/sbin/service的一个可执行的脚本，其内容如下：

1. #!/bin/sh
2. ###########################################################################
3. # /usr/bin/service
4. #
5. # A convenient wrapper for the /etc/init.d init scripts. 
6. #（不过是/etc/init.d/ 目录下各种可执行脚本的一个为了方便调用而增加的一个包装而已。）
7. #
8. ###########################################################################
9. is_ignored_file() {
10.         case "$1" in
11.                 skeleton | README | *.dpkg-dist | *.dpkg-old | rc | rcS | single | reboot | bootclean.sh)
12.                         return 0
13.                 ;;
14.         esac
15.         return 1
16. }
17.  
18. VERSION="`basename $0` ver. 0.91-ubuntu1"
19. USAGE="Usage: `basename $0` < option > | --status-all | \
20. [ service_name [ command | --full-restart ] ]"
21. SERVICE=
22. ACTION=
23. SERVICEDIR="/etc/init.d"
24. OPTIONS=
25. # 没有给出参数，打印提示信息
26. if [ $# -eq 0 ]; then
27.    echo "${USAGE}" >&2
28.    exit 1
29. fi
30. # 改变目录
31. cd /
32. while [ $# -gt 0 ]; do
33.   case "${1}" in           
34.     --help | -h | --h* )     # 处理 service --help / -h / --h
35.        echo "${USAGE}" >&2
36.        exit 0
37.        ;;
38.     --version | -V )         # 处理 service --version / -V 
39.        echo "${VERSION}" >&2
40.        exit 0
41.        ;;
42.     *)                       # 处理 其它的情况
43.        # 没有命令名，并且参数个数为1，并且此参数为 --status-all. 也就是 "service --status-all"
44.        if [ -z "${SERVICE}" -a $# -eq 1 -a "${1}" = "--status-all" ]; then
45.           cd ${SERVICEDIR}          # 进入目录/etc/init.d/
46.           for SERVICE in * ; do     # 对目录/etc/init.d/中的每一个文件进行下面的处理 
47.             case "${SERVICE}" in    # 忽略下面一些的文件的执行
48.               functions | halt | killall | single| linuxconf| kudzu)
49.                   ;;
50.               *)  # 其它不可忽略的情况的处理
51.                   # 文件不是可以忽略的，并且还具有可执行权限
52.                 if ! is_ignored_file "${SERVICE}" \
53.                     && [ -x "${SERVICEDIR}/${SERVICE}" ]; then
54.                         if ! grep -qs "\Wstatus)" "$SERVICE"; then
55.                           #printf " %s %-60s %s\n" "[?]" "$SERVICE:" "unknown" 1>&2
56.                           echo " [ ? ] $SERVICE" 1>&2
57.                           continue
58.                         else    # 获得对应命令的status
59.                           out=$(env -i LANG="$LANG" PATH="$PATH" TERM="$TERM" "$SERVICEDIR/$SERVICE" status 2>&1)    
60.                         #上面的env -i正确执行完成，并且执行的结果$out非空(true)，说明对应的命令正在运行
61.                           if [ "$?" = "0" -a -n "$out" ]; then
62.                             #printf " %s %-60s %s\n" "[+]" "$SERVICE:" "running"
63.                             echo " [ + ] $SERVICE"
64.                             continue
65.                           else # 对应的命令没有正在运行
66.                             #printf " %s %-60s %s\n" "[-]" "$SERVICE:" "NOT running"
67.                             echo " [ - ] $SERVICE"
68.                             continue
69.                           fi
70.                         fi
71.                   #env -i LANG="$LANG" PATH="$PATH" TERM="$TERM" "$SERVICEDIR/$SERVICE" status
72.                 fi
73.                 ;;
74.             esac
75.           done
76.           exit 0
77.        # 如果参数的个数位2，并且第二个参数为--full-restart
78.        elif [ $# -eq 2 -a "${2}" = "--full-restart" ]; then
79.           SERVICE="${1}"   # 先停止，然后开启
80.           if [ -x "${SERVICEDIR}/${SERVICE}" ]; then
81.             env -i LANG="$LANG" PATH="$PATH" TERM="$TERM" "$SERVICEDIR/$SERVICE" stop
82.             env -i LANG="$LANG" PATH="$PATH" TERM="$TERM" "$SERVICEDIR/$SERVICE" start
83.             exit $?
84.           fi
85.        elif [ -z "${SERVICE}" ]; then    # 给在开头定义的变量赋值
86.          SERVICE="${1}"
87.        elif [ -z "${ACTION}" ]; then     # 给在开头定义的变量赋值
88.          ACTION="${1}"
89.        else
90.          OPTIONS="${OPTIONS} ${1}"       # 给在开头定义的变量赋值
91.        fi
92.        shift
93.        ;;
94.    esac
95. done
96.  
97. # 判断是否存在对应命令的配置文件
98. if [ -r "/etc/init/${SERVICE}.conf" ]; then
99.    # Upstart configuration exists for this job
100.    case "${ACTION}" in
101.       start|stop|restart|status|reload)
102.          # Action is a valid upstart action
103.          exec ${ACTION} ${SERVICE} ${OPTIONS}    # 根据参数执行
104.       ;;
105.       force-reload)
106.          # Upstart just uses reload for force-reload
107.          exec reload ${SERVICE} ${OPTIONS}       # 根据参数执行
108.       ;;
109.    esac
110. fi
111.  

 # env -i 删除所以的环境变量，仅仅保留LANG PATH TERM三个环境变量，然后执行安装参数执行命令

1. # Otherwise, use the traditional sysvinit
2. if [ -x "${SERVICEDIR}/${SERVICE}" ]; then
3.    exec env -i LANG="$LANG" PATH="$PATH" TERM="$TERM" "$SERVICEDIR/$SERVICE" ${ACTION} ${OPTIONS}
4. else
5.    echo "${SERVICE}: unrecognized service" >&2
6.    exit 1
7. fi