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Linux中 service 命令浅析

Linux中 service 命令浅析

作者: 量U移动广告归因 | 来源:发表于2021-07-02 21:35 被阅读0次

    Service命令在不同的Linux发行版中都有不同的实现，并且同一发行版不同的版本号之间功能也不尽相同
    但无论怎么变化，Service命令永远都只是一组脚本
    下面对比的是 CentOS6.5、CentOS8.3以及Ubuntu20.04，Service命令的代码变化

    //CentOS6.5 位于/sbin/service
#!/bin/sh

. /etc/init.d/functions

VERSION="$(basename $0) ver. 0.91"
USAGE="Usage: $(basename $0) < option > | --status-all | \
[ service_name [ command | --full-restart ] ]"
SERVICE=
SERVICEDIR="/etc/init.d"
OPTIONS=

if [ $# -eq 0 ]; then
   echo "${USAGE}" >&2
   exit 1
fi

cd /
while [ $# -gt 0 ]; do
  case "${1}" in
    --help | -h | --h* )
       echo "${USAGE}" >&2
       exit 0
       ;;
    --version | -V )
       echo "${VERSION}" >&2
       exit 0
       ;;
    *)
       if [ -z "${SERVICE}" -a $# -eq 1 -a "${1}" = "--status-all" ]; then
          cd ${SERVICEDIR}
          for SERVICE in * ; do
            case "${SERVICE}" in
              functions | halt | killall | single| linuxconf| kudzu)
                  ;;
              *)
                if ! is_ignored_file "${SERVICE}" \
            && [ -x "${SERVICEDIR}/${SERVICE}" ]; then
                  env -i PATH="$PATH" TERM="$TERM" "${SERVICEDIR}/${SERVICE}" status
                fi
                ;;
            esac
          done
          exit 0
       elif [ $# -eq 2 -a "${2}" = "--full-restart" ]; then
          SERVICE="${1}"
          if [ -x "${SERVICEDIR}/${SERVICE}" ]; then
            env -i PATH="$PATH" TERM="$TERM" "${SERVICEDIR}/${SERVICE}" stop
            env -i PATH="$PATH" TERM="$TERM" "${SERVICEDIR}/${SERVICE}" start
            exit $?
          fi
       elif [ -z "${SERVICE}" ]; then
         SERVICE="${1}"
       else
         OPTIONS="${OPTIONS} ${1}"
       fi
       shift
       ;;
   esac
done

if [ -f "${SERVICEDIR}/${SERVICE}" ]; then
   env -i PATH="$PATH" TERM="$TERM" "${SERVICEDIR}/${SERVICE}" ${OPTIONS}
else
   echo $"${SERVICE}: unrecognized service" >&2
   exit 1
fi

//CentOS8.3 位于/sbin/service 实际链接指向 /usr/sbin/service
#!/bin/bash

. /etc/init.d/functions

VERSION="$(basename $0) ver. 1.1"
USAGE="Usage: $(basename $0) < option > | --status-all | \
[ service_name [ command | --full-restart ] ]"
SERVICEDIR="/etc/init.d"
ACTIONDIR="/usr/libexec/initscripts/legacy-actions"
SERVICE=
ACTION=
OPTIONS=

if [ $# -eq 0 ]; then
   echo "${USAGE}" >&2
   exit 1
fi

cd /
while [ $# -gt 0 ]; do
  case "${1}" in
    --help | -h | --h* )
       echo "${USAGE}" >&2
       exit 0
       ;;
    --version | -V )
       echo "${VERSION}" >&2
       exit 0
       ;;
    --ignore-dependencies)
       export SYSTEMCTL_IGNORE_DEPENDENCIES=1
       shift
       ;;
    --skip-redirect)
       export SYSTEMCTL_SKIP_REDIRECT=1
       shift
       ;;
    *)
       if [ -z "${SERVICE}" -a $# -eq 1 -a "${1}" = "--status-all" ]; then
          cd ${SERVICEDIR}
          for SERVICE in * ; do
            case "${SERVICE}" in
              functions | halt | killall | single| linuxconf| kudzu)
                  ;;
              *)
                if ! is_ignored_file "${SERVICE}" \
            && [ -x "${SERVICEDIR}/${SERVICE}" ]; then
                  env -i PATH="$PATH" TERM="$TERM" "${SERVICEDIR}/${SERVICE}" status
                fi
                ;;
            esac
          done
          exit 0
       elif [ $# -eq 2 -a "${2}" = "--full-restart" ]; then
          SERVICE="${1}"
          if [ -x "${SERVICEDIR}/${SERVICE}" ]; then
            env -i PATH="$PATH" TERM="$TERM" "${SERVICEDIR}/${SERVICE}" stop
            env -i PATH="$PATH" TERM="$TERM" "${SERVICEDIR}/${SERVICE}" start
            exit $?
          fi
       elif [ -z "${SERVICE}" ]; then
         SERVICE="${1}"
       elif [ -z "${ACTION}" ]; then
         ACTION="${1}"
       else
         OPTIONS="${OPTIONS} ${1}"
       fi
       shift
       ;;
   esac
done

if [ -f "${SERVICEDIR}/${SERVICE}" ]; then
   # LSB daemons that dies abnormally in systemd looks alive in systemd's eyes due to RemainAfterExit=yes
   # lets reap them before next start
   if [ "${ACTION}" = "start" ] && \
   systemctl show -p ActiveState ${SERVICE}.service | grep -q '=active$' && \
   systemctl show -p SubState ${SERVICE}.service | grep -q '=exited$' ; then
       /bin/systemctl stop ${SERVICE}.service
   fi
   # Workaround to be able to "stop" network.service when it's in inactive state using service instead of systemctl
   # Useful for manual testing of network
   if [ "${SERVICE}" = 'network' ] && [ "${ACTION}" = 'stop' ] && \
   [ "$(systemctl show -p ActiveState network.service --value)" = 'inactive' ] && \
   [ "$(systemctl show -p SourcePath network.service --value)" = '/etc/rc.d/init.d/network' ]; then
       export SYSTEMCTL_SKIP_REDIRECT=1
   fi
   env -i PATH="$PATH" TERM="$TERM" SYSTEMCTL_IGNORE_DEPENDENCIES=${SYSTEMCTL_IGNORE_DEPENDENCIES} SYSTEMCTL_SKIP_REDIRECT=${SYSTEMCTL_SKIP_REDIRECT} "${SERVICEDIR}/${SERVICE}" ${ACTION} ${OPTIONS}
elif [ -n "${ACTION}" ] && [ -x "${ACTIONDIR}/${SERVICE}/${ACTION}" ]; then
   env -i PATH="$PATH" TERM="$TERM" SYSTEMCTL_IGNORE_DEPENDENCIES=${SYSTEMCTL_IGNORE_DEPENDENCIES} SYSTEMCTL_SKIP_REDIRECT=${SYSTEMCTL_SKIP_REDIRECT} "${ACTIONDIR}/${SERVICE}/${ACTION}" ${OPTIONS}
elif `echo $ACTION | grep -Eqw "start|stop|restart|try-restart|reload|force-reload|status|condrestart"` ; then
   SERVICE_MANGLED=$(/usr/bin/systemd-escape --mangle ${SERVICE})
   echo $"Redirecting to /bin/systemctl ${ACTION}${OPTIONS:+ }${OPTIONS} ${SERVICE_MANGLED}" >&2
   exec /bin/systemctl ${ACTION} ${OPTIONS} ${SERVICE_MANGLED}
else
   echo $"The service command supports only basic LSB actions (start, stop, restart, try-restart, reload, force-reload, status). For other actions, please try to use systemctl." >&2
   exit 2
fi

//Ubuntu20.04 位于/usr/sbin/service
#!/bin/bash

###########################################################################
# /usr/bin/service
#
# A convenient wrapper for the /etc/init.d init scripts.
#
# This script is a modified version of the /sbin/service utility found on
# Red Hat/Fedora systems (licensed GPLv2+).
#
# Copyright (C) 2006 Red Hat, Inc. All rights reserved.
# Copyright (C) 2008 Canonical Ltd.
#   * August 2008 - Dustin Kirkland <kirkland@canonical.com>
# Copyright (C) 2013 Michael Stapelberg <stapelberg@debian.org>
#
# This program is free software; you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation; either version 2 of the License, or
# (at your option) any later version.
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with this program; if not, write to the Free Software
# Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
#
# On Debian GNU/Linux systems, the complete text of the GNU General
# Public License can be found in `/usr/share/common-licenses/GPL-2'.
###########################################################################


is_ignored_file() {
    case "$1" in
        skeleton | README | *.dpkg-dist | *.dpkg-old | rc | rcS | single | reboot | bootclean.sh)
            return 0
        ;;
    esac
    return 1
}

VERSION="`basename $0` ver. 1.57"
USAGE="Usage: `basename $0` < option > | --status-all | \
[ service_name [ command | --full-restart ] ]"
SERVICE=
ACTION=
SERVICEDIR="/etc/init.d"
OPTIONS=
is_systemd=


if [ $# -eq 0 ]; then
   echo "${USAGE}" >&2
   exit 1
fi

if [ -d /run/systemd/system ]; then
   is_systemd=1
fi

cd /
while [ $# -gt 0 ]; do
  case "${1}" in
    --help | -h | --h* )
       echo "${USAGE}" >&2
       exit 0
       ;;
    --version | -V )
       echo "${VERSION}" >&2
       exit 0
       ;;
    *)
       if [ -z "${SERVICE}" -a $# -eq 1 -a "${1}" = "--status-all" ]; then
          cd ${SERVICEDIR}
          for SERVICE in * ; do
            case "${SERVICE}" in
              functions | halt | killall | single| linuxconf| kudzu)
                  ;;
              *)
                if ! is_ignored_file "${SERVICE}" \
            && [ -x "${SERVICEDIR}/${SERVICE}" ]; then
                        out=$(env -i LANG="$LANG" LANGUAGE="$LANGUAGE" LC_CTYPE="$LC_CTYPE" LC_NUMERIC="$LC_NUMERIC" LC_TIME="$LC_TIME" LC_COLLATE="$LC_COLLATE" LC_MONETARY="$LC_MONETARY" LC_MESSAGES="$LC_MESSAGES" LC_PAPER="$LC_PAPER" LC_NAME="$LC_NAME" LC_ADDRESS="$LC_ADDRESS" LC_TELEPHONE="$LC_TELEPHONE" LC_MEASUREMENT="$LC_MEASUREMENT" LC_IDENTIFICATION="$LC_IDENTIFICATION" LC_ALL="$LC_ALL" PATH="$PATH" TERM="$TERM" "$SERVICEDIR/$SERVICE" status 2>&1)
                        retval=$?
                        if echo "$out" | egrep -iq "usage:"; then
                          #printf " %s %-60s %s\n" "[?]" "$SERVICE:" "unknown" 1>&2
                          echo " [ ? ]  $SERVICE" 1>&2
                          continue
                        else
                          if [ "$retval" = "0" -a -n "$out" ]; then
                            #printf " %s %-60s %s\n" "[+]" "$SERVICE:" "running"
                            echo " [ + ]  $SERVICE"
                            continue
                          else
                            #printf " %s %-60s %s\n" "[-]" "$SERVICE:" "NOT running"
                            echo " [ - ]  $SERVICE"
                            continue
                          fi
                        fi
                  #env -i LANG="$LANG" LANGUAGE="$LANGUAGE" LC_CTYPE="$LC_CTYPE" LC_NUMERIC="$LC_NUMERIC" LC_TIME="$LC_TIME" LC_COLLATE="$LC_COLLATE" LC_MONETARY="$LC_MONETARY" LC_MESSAGES="$LC_MESSAGES" LC_PAPER="$LC_PAPER" LC_NAME="$LC_NAME" LC_ADDRESS="$LC_ADDRESS" LC_TELEPHONE="$LC_TELEPHONE" LC_MEASUREMENT="$LC_MEASUREMENT" LC_IDENTIFICATION="$LC_IDENTIFICATION" LC_ALL="$LC_ALL" PATH="$PATH" TERM="$TERM" "$SERVICEDIR/$SERVICE" status
                fi
                ;;
            esac
          done
          exit 0
       elif [ $# -eq 2 -a "${2}" = "--full-restart" ]; then
          SERVICE="${1}"
          # On systems using systemd, we just perform a normal restart:
          # A restart with systemd is already a full restart.
          if [ -n "$is_systemd" ]; then
             ACTION="restart"
          else
             if [ -x "${SERVICEDIR}/${SERVICE}" ]; then
               env -i LANG="$LANG" LANGUAGE="$LANGUAGE" LC_CTYPE="$LC_CTYPE" LC_NUMERIC="$LC_NUMERIC" LC_TIME="$LC_TIME" LC_COLLATE="$LC_COLLATE" LC_MONETARY="$LC_MONETARY" LC_MESSAGES="$LC_MESSAGES" LC_PAPER="$LC_PAPER" LC_NAME="$LC_NAME" LC_ADDRESS="$LC_ADDRESS" LC_TELEPHONE="$LC_TELEPHONE" LC_MEASUREMENT="$LC_MEASUREMENT" LC_IDENTIFICATION="$LC_IDENTIFICATION" LC_ALL="$LC_ALL" PATH="$PATH" TERM="$TERM" "$SERVICEDIR/$SERVICE" stop
               env -i LANG="$LANG" LANGUAGE="$LANGUAGE" LC_CTYPE="$LC_CTYPE" LC_NUMERIC="$LC_NUMERIC" LC_TIME="$LC_TIME" LC_COLLATE="$LC_COLLATE" LC_MONETARY="$LC_MONETARY" LC_MESSAGES="$LC_MESSAGES" LC_PAPER="$LC_PAPER" LC_NAME="$LC_NAME" LC_ADDRESS="$LC_ADDRESS" LC_TELEPHONE="$LC_TELEPHONE" LC_MEASUREMENT="$LC_MEASUREMENT" LC_IDENTIFICATION="$LC_IDENTIFICATION" LC_ALL="$LC_ALL" PATH="$PATH" TERM="$TERM" "$SERVICEDIR/$SERVICE" start
               exit $?
             fi
          fi
       elif [ -z "${SERVICE}" ]; then
         SERVICE="${1}"
       elif [ -z "${ACTION}" ]; then
         ACTION="${1}"
       else
         OPTIONS="${OPTIONS} ${1}"
       fi
       shift
       ;;
   esac
done

run_via_sysvinit() {
   # Otherwise, use the traditional sysvinit
   if [ -x "${SERVICEDIR}/${SERVICE}" ]; then
      exec env -i LANG="$LANG" LANGUAGE="$LANGUAGE" LC_CTYPE="$LC_CTYPE" LC_NUMERIC="$LC_NUMERIC" LC_TIME="$LC_TIME" LC_COLLATE="$LC_COLLATE" LC_MONETARY="$LC_MONETARY" LC_MESSAGES="$LC_MESSAGES" LC_PAPER="$LC_PAPER" LC_NAME="$LC_NAME" LC_ADDRESS="$LC_ADDRESS" LC_TELEPHONE="$LC_TELEPHONE" LC_MEASUREMENT="$LC_MEASUREMENT" LC_IDENTIFICATION="$LC_IDENTIFICATION" LC_ALL="$LC_ALL" PATH="$PATH" TERM="$TERM" "$SERVICEDIR/$SERVICE" ${ACTION} ${OPTIONS}
   else
      echo "${SERVICE}: unrecognized service" >&2
      exit 1
   fi
}

update_openrc_started_symlinks() {
   # maintain the symlinks of /run/openrc/started so that
   # rc-status works with the service command as well
   if [ -d /run/openrc/started ] ; then
      case "${ACTION}" in
      start)
         if [ ! -h /run/openrc/started/$SERVICE ] ; then
            ln -s $SERVICEDIR/$SERVICE /run/openrc/started/$SERVICE || true
         fi
      ;;
      stop)
         rm /run/openrc/started/$SERVICE || true
      ;;
      esac
   fi
}

# When this machine is running systemd, standard service calls are turned into
# systemctl calls.
if [ -n "$is_systemd" ]
then
   UNIT="${SERVICE%.sh}.service"
   # avoid deadlocks during bootup and shutdown from units/hooks
   # which call "invoke-rc.d service reload" and similar, since
   # the synchronous wait plus systemd's normal behaviour of
   # transactionally processing all dependencies first easily
   # causes dependency loops
   if ! systemctl --quiet is-active multi-user.target; then
       sctl_args="--job-mode=ignore-dependencies"
   fi

   case "${ACTION}" in
      restart|status|try-restart)
         exec systemctl $sctl_args ${ACTION} ${UNIT}
      ;;
      start|stop)
         # Follow the principle of least surprise for SysV people:
         # When running "service foo stop" and foo happens to be a service that
         # has one or more .socket files, we also stop the .socket units.
         # Users who need more control will use systemctl directly.
         for unit in $(systemctl list-unit-files --full --type=socket 2>/dev/null | sed -ne 's/\.socket\s*[a-z]*\s*$/.socket/p'); do
             if [ "$(systemctl -p Triggers show $unit)" = "Triggers=${UNIT}" ]; then
                systemctl $sctl_args ${ACTION} $unit
             fi
         done
         exec systemctl $sctl_args ${ACTION} ${UNIT}
      ;;
      reload)
         _canreload="$(systemctl -p CanReload show ${UNIT} 2>/dev/null)"
         if [ "$_canreload" = "CanReload=no" ]; then
            # The reload action falls back to the sysv init script just in case
            # the systemd service file does not (yet) support reload for a
            # specific service.
            run_via_sysvinit
         else
            exec systemctl $sctl_args reload "${UNIT}"
         fi
         ;;
      force-stop)
         exec systemctl --signal=KILL kill "${UNIT}"
         ;;
      force-reload)
         _canreload="$(systemctl -p CanReload show ${UNIT} 2>/dev/null)"
         if [ "$_canreload" = "CanReload=no" ]; then
            exec systemctl $sctl_args restart "${UNIT}"
         else
            exec systemctl $sctl_args reload "${UNIT}"
         fi
         ;;
      *)
         # We try to run non-standard actions by running
         # the init script directly.
         run_via_sysvinit
         ;;
   esac
fi

update_openrc_started_symlinks
run_via_sysvinit

    可以看得出，无论是Red Hat系还是Debian系，service命令的前半部分的逻辑都是十分相似的，不同的是后面部分，CentOS8.3在后面加上了 systemctl 命令的逻辑，这个命令在 CentOS6.5中是没有的，而 Ubuntu的后面部分也是自己特色的实现，不过这些这里暂且不表，这里只浅析一下 service --status-all 这个参数在不同发行版中的不同表现

    if [ -z "${SERVICE}" -a $# -eq 1 -a "${1}" = "--status-all" ]; then
          cd ${SERVICEDIR}
          for SERVICE in * ; do
            case "${SERVICE}" in
              functions | halt | killall | single| linuxconf| kudzu)
                  ;;
              *)
                if ! is_ignored_file "${SERVICE}" \
            && [ -x "${SERVICEDIR}/${SERVICE}" ]; then
                  env -i PATH="$PATH" TERM="$TERM" "${SERVICEDIR}/${SERVICE}" status
                fi
                ;;
            esac
          done
          exit 0
......

    从这一段代码可以看出，service加上--status-all参数后，就会将 /etc/init.d/ 目录下的所有脚本带上 status 参数循环执行一遍然后再对输出进行过滤格式化，但诡异的是，CentOS8.3 把 /etc/init.d/ 目录下的所有应用启动脚本全部删除了，空空如也


    没有启动脚本了

    所以在 CentOS8.3 中，执行 service --status-all 是没有任何输出的，不信大家可以试一下，这时如果想得知哪个服务是否安装了，只能使用 ps -aux 查看进程或者使用 netstat -tnlp 查看某个端口了，又或者使用包管理工具 rpm 来查看
    CentOS6.5 和 Ubuntu20.04下这个命令是没有问题的

    root@localhost:~# service --status-all
 [ + ]  aegis
 [ + ]  apache2
 [ - ]  apache-htcacheclean
 [ + ]  apparmor
 [ + ]  atd
 [ + ]  chrony
 [ - ]  console-setup.sh
 [ + ]  cron
 [ + ]  dbus
 [ - ]  fio
 [ + ]  grub-common
 [ - ]  hwclock.sh
 [ - ]  irqbalance
 [ - ]  keyboard-setup.sh
 [ + ]  kmod
 [ - ]  nginx
 [ - ]  ntp
 [ - ]  plymouth
 [ - ]  plymouth-log
 [ + ]  procps
....
    Ubuntu20.04

    当系统引入 systemctl 命令之后，service本质上就是对 systemctl 进行了一次包装，实际都是执行这个命令来调用.service配置文件（位于 /usr/lib/systemd/system ）进行控制操作，这一点 Ubuntu20.04 和 CentOS8.3 很像，不像 CentOS6.5 ，脚本中是直接与应用二进制文件打交道。
    所以对服务的操控可以有两种写法(后者直接使用了 systemctl 命令调用 .service 配置文件)

    1. service apache2 start

    2.systemctl start apache2.service

    service的控制单元是一个个的 .service 配置文件，每个 .service 文件对应一个服务的控制操作，.service文件的书写有一定的规范，下面是 Ubuntu20.04下 apache2.service 的配置内容( CentOS 中是 httpd.service )

    [Unit]
Description=The Apache HTTP Server
After=network.target remote-fs.target nss-lookup.target
Documentation=https://httpd.apache.org/docs/2.4/

[Service]
Type=forking
Environment=APACHE_STARTED_BY_SYSTEMD=true
ExecStart=/usr/sbin/apachectl start
ExecStop=/usr/sbin/apachectl stop
ExecReload=/usr/sbin/apachectl graceful
PrivateTmp=true
Restart=on-abort

[Install]
WantedBy=multi-user.target

    可以看出，service 配置文件才是真正与二进制文件进行关联的

    再来看看 /etc/init.d/apache2 脚本

    再次说明，CentOS8.3 是没有这个脚本的，而 CentOS6.5 是直接与二进制文件进行交互，这里就以 Ubuntu20.04 进行说明
    前面说过，service --status-all 实际上是将这个目录下的脚本全部循环加上 status 参数执行一遍，也就是说
    /etc/init.d/apache2 status 这条命令是会被执行的

    root@localhost:~# /etc/init.d/apache2 status
● apache2.service - The Apache HTTP Server
     Loaded: loaded (/lib/systemd/system/apache2.service; enabled; vendor preset: enabled)
     Active: active (running) since Mon 2021-06-28 13:49:56 CST; 20h ago
       Docs: https://httpd.apache.org/docs/2.4/
    Process: 6856 ExecReload=/usr/sbin/apachectl graceful (code=exited, status=0/SUCCESS)
   Main PID: 2003 (apache2)
      Tasks: 55 (limit: 2193)
     Memory: 8.4M
     CGroup: /system.slice/apache2.service
             ├─2003 /usr/sbin/apache2 -k start
             ├─6860 /usr/sbin/apache2 -k start
             └─6861 /usr/sbin/apache2 -k start

Jun 28 13:49:56 localhost systemd[1]: Starting The Apache HTTP Server...
Jun 28 13:49:56 localhost apachectl[2002]: AH00558: apache2: Could not reliably determine t…ssage
Jun 28 13:49:56 localhost systemd[1]: Started The Apache HTTP Server.
Jun 29 00:01:00 localhost systemd[1]: Reloading The Apache HTTP Server.
Jun 29 00:01:00 localhost apachectl[6859]: AH00558: apache2: Could not reliably determine t…ssage
Jun 29 00:01:00 localhost systemd[1]: Reloaded The Apache HTTP Server.
Hint: Some lines were ellipsized, use -l to show in full.

    以上是直接执行 /etc/init.d/apache2 status 的输出结果，但为何执行 service --status-all 又变成了列表形式的呢，那时因为对输出结果进行了一系列变换格式化操作，现在我们看下为何 /etc/init.d/apache2 status 的输出结果是这样，本质上是哪部分代码被执行了
    用文本编辑器打开 /etc/init.d/apache2 脚本，大概在 53 行处

    . /lib/lsb/init-functions  //实际上指向 /usr/lib/lsb/init-functions

    输出的功能性代码就在这个引入脚本里，再打开这个脚本，在末尾处

    for hook in $(run-parts --lsbsysinit --list /lib/lsb/init-functions.d 2>/dev/null); do
    [ -r $hook ] && . $hook || true
done

    又是循环执行了脚本，再次打开 /lib/lsb/init-functions.d （实际指向是 /usr/lib/lsb/init-functions.d ）


    init-functions.d

    这里面的脚本都会执行一遍，重点就是那个 systemd ，用文本编辑器打开，最后几行代码

        case "$argument" in
        start|stop|restart|reload|force-reload|try-restart|status)
            systemctl_redirect $executable $argument
            exit $?
            ;;
    esac

    systemctl_redirect 这个函数的实现在 systemd 文本的前半部分

    systemctl_redirect () {
    local s
    local rc
    local prog=${1##*/}
    local command=$2

    case "$command" in
        start)
            s="Starting $prog (via systemctl)"
            ;;
        stop)
            s="Stopping $prog (via systemctl)"
            ;;
        reload|force-reload)
            s="Reloading $prog configuration (via systemctl)"
            ;;
        try-restart)
            s="Restarting $prog if running (via systemctl)"
            ;;
        restart)
            s="Restarting $prog (via systemctl)"
            ;;
    esac

    service="${prog%.sh}.service"

    # avoid deadlocks during bootup and shutdown from units/hooks
    # which call "invoke-rc.d service reload" and similar, since
    # the synchronous wait plus systemd's normal behaviour of
    # transactionally processing all dependencies first easily
    # causes dependency loops
    if ! OUT=$(systemctl is-system-running 2>/dev/null) && [ "$OUT" != "degraded" ]; then
        sctl_args="--job-mode=ignore-dependencies"
    fi

    [ "$command" = status ] || log_daemon_msg "$s" "$service"
    /bin/systemctl --no-pager $sctl_args $command "$service" //这行才是重点
    rc=$?
    [ "$command" = status ] || log_end_msg $rc

    return $rc
}

    /bin/systemctl --no-pager $sctl_args $command "$service"这一行才是重点，大概在全文的 82 行左右
    如果把里面的变量替换展开，最后执行的命令行大概就是这样
    /bin/systemctl --no-pager status apache2.service
    直接运行这条命令，可以得到和 /etc/init.d/apache2 status 一样的输出

    结论

    没想到 service --staus-all 最后还是依赖于 systemctl 这个命令，不过 /etc/init.d 里面大量的脚本只是为了使 service --staus-all 这条命令有效，是不是有点浪费，如果像 CentOS8.3 那样直接删掉，是不是更显得简洁，你觉得呢？

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