systemctl 和 service 命令的区别

Question

systemd为我们提供了systemctl命令套件，该套件主要用于使服务在启动时启动。我们还可以在 的帮助下启动、停止、重新加载、重新启动和检查服务的状态systemctl。

例如，我们可以这样做，sudo systemctl enable service_name并且service_name会在启动时自动启动。我们还可以禁用在启动时不启动的服务。

service和systemctl命令之间的唯一区别是systemctl可用于在运行时启动服务吗？我们可以systemctl在任何服务上使用吗？还有哪些其他显着差异？

Answer 1

The service command is a wrapper script that allows system administrators to start, stop, and check the status of services without worrying too much about the actual init system being used. Prior to systemd's introduction, it was a wrapper for /etc/init.d scripts and Upstart's initctl command, and now it is a wrapper for these two and systemctl as well.

Use the source, Luke!

It checks for Upstart:

# Operate against system upstart, not session
unset UPSTART_SESSION
if [ -r "/etc/init/${SERVICE}.conf" ] && which initctl >/dev/null \
   && initctl version 2>/dev/null | grep -q upstart \
   && initctl status ${SERVICE} 2>/dev/null 1>/dev/null
then
   # Upstart configuration exists for this job and we're running on upstart

If that doesn't work, it looks for systemd:

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

...

# When this machine is running systemd, standard service calls are turned into
# systemctl calls.
if [ -n "$is_systemd" ]
then

And if that fails as well, it falls back to System V /etc/init.d scripts:

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
}

...
run_via_sysvinit

Since the service command is a fairly simple wrapper, it only supports a limited subset of actions compared to what the actual init system might provide.

For portability over various versions of Ubuntu, users can reliably use the service command to start, stop, restart or examine the status of a service. For more complex tasks, however, the actual command being used, be that initctl or systemctl or the /etc/init.d script might have to be used directly.

Further, being a wrapper, the service script in some cases also does more than the direct equivalent command might do. For example:

• It always executes /etc/init.d scripts in a clean environment. (Note the long env command invocation in the run_via_sysvinit function above.)
• It maps restart on Upstart systems to a combination of stop/start, since a plain initctl restart will error out if the service isn't running already.

• 它在停止具有关联套接字的 systemd 服务时停止套接字：

  case "${ACTION}" in
    restart|status)
       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.
  

Upstart 服务直接在服务配置文件中启用（或通过覆盖禁用），并且 System V 脚本使用update-rc.d命令启用或禁用（管理/etc/rc*目录中的符号链接），因此该service命令从未涉及在启动时启用或禁用服务.

Answer 2

• systemd 向后兼容 SysV。
• 在启动时并行加载服务
• 它提供按需激活服务
• 它是基于依赖的
• 还有更多我猜...

有很多比你提到systemctl的能力。

systemd 与单元一起工作，有不同类型的单元：目标、服务、套接字等。目标与运行级别的概念相同，它们是一组单元。

您可以使用systemctl来设置或获取默认系统目标。

systemctl get-default

您可以进入其他目标：

systemctl isolate multiuser.target

其他目标是：多用户、图形、recue、紧急情况、重启、关机。

正如您所说，您可以systemctl用来管理服务，我所知道的与服务管理相关的其他一些命令是：

# Restarts a service only if it is running.
systemctl try-restart name.service

# Reloads configuration if it's possible.
systemctl reload name.service

# try to reload but if it's not possible restarts the service
systemctl reload-or-restart name.service

您可以使用它来了解服务状态：

systemctl status name.service

systemctl is-active name.service # running
systemctl is-enabled name.service # will be activated when booting
systemctl is-failed name.service # failed to load

您可以屏蔽或取消屏蔽服务：

systemctl mask name.service
systemctl unmask name.service

你屏蔽了一个服务，它会链接到/dev/null，所以手动或自动其他服务不能激活/启用它。（你应该先揭开它的面具）。

systemctl 的另一个用法是列出单位：

systemctl list-units

其中列出了所有类型的单位，已加载和活动。

列出服务单位：

systemctl list-units --type=service

或者列出所有可用的单位，而不仅仅是加载和激活的单位：

systemctl list-unit-files

您可以创建别名甚至控制远程机器

systemctl --host ravexina@192.168.56.4 list-units

另一方面service做它必须做的事情，管理服务并且与其他人的业务无关；）