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pinewall translating
Systemd Services: Beyond Starting and Stopping
======
![](https://www.linux.com/sites/lcom/files/styles/rendered_file/public/systemd-minetest-2.jpg?itok=bXO0ggHL)
[In the previous article][1], we showed how to create a systemd service that you can run as a regular user to start and stop your game server. As it stands, however, your service is still not much better than running the server directly. Let's jazz it up a bit by having it send out emails to the players, alerting them when the server becomes available and warning them when it is about to be turned off:
```
# minetest.service
[Unit]
Description= Minetest server
Documentation= https://wiki.minetest.net/Main_Page
[Service]
Type= simple
ExecStart= /usr/games/minetest --server
ExecStartPost= /home/<username>/bin/mtsendmail.sh "Ready to rumble?" "Minetest Starting up"
TimeoutStopSec= 180
ExecStop= /home/<username>/bin/mtsendmail.sh "Off to bed. Nightie night!" "
  Minetest Stopping in 2 minutes"
ExecStop= /bin/sleep 120
ExecStop= /bin/kill -2 $MAINPID
```
There are a few new things in here. First, there's the `ExecStartPost` directive. You can use this directive for anything you want to run right after the main application starts. In this case, you run a custom script, `mtsendmail` (see below), that sends an email to your friends telling them that the server is up.
```
#!/bin/bash
# mtsendmail
echo $1 | mutt -F /home/<username>/.muttrc -s "$2" my_minetest@mailing_list.com
```
You can use [Mutt][2], a command-line email client, to shoot off your messages. Although the script shown above is to all practical effects only one line long, remember you can't have a line with pipes and redirections as a systemd unit argument, so you have to wrap it in a script.
For the record, there is also an `ExecStartPre` directive for things you want to execute before starting the service proper.
Next up, you have a block of commands that close down the server. The `TimeoutStopSec` directive pushes up the time before systemd bails on shutting down the service. The default time out value is round about 90 seconds. Anything longer, and systemd will force the service to close down and report a failure. But, as you want to give your users a couple of minutes before closing the server completely, you are going to push the default up to three minutes. This will stop systemd from thinking the closedown has failed.
Then the close down proper starts. Although there is no `ExecStopPre` as such, you can simulate running stuff before closing down your server by using more than one `ExecStop` directive. They will be executed in order, from topmost to bottommost, and will allow you to send out a message before the server is actually stopped.
With that in mind, the first thing you do is shoot off an email to your friends, warning them the server is going down. Then you wait two minutes. Finally you close down the server. Minetest likes to be closed down with [Ctrl] + [c], which translates into an interrupt signal ( _SIGINT_ ). That is what you do when you issue the `kill -2 $MAINPID` command. `$MAINPID` is a systemd variable for your service that points to the PID of the main application.
This is much better! Now, when you run
```
systemctl --user start minetest
```
The service will start up the Minetest server and send out an email to your users. Likewise when you are about to close down, but giving two minutes to users to log off.
### Starting at Boot
The next step is to make your service available as soon as the machine boots up, and close down when you switch it off at night.
Start be moving your service out to where the system services live, The directory youa re looking for is _/etc/systemd/system/_ :
```
sudo mv /home/<username>/.config/systemd/user/minetest.service /etc/systemd/system/
```
If you were to try and run the service now, it would have to be with superuser privileges:
```
sudo systemctl start minetest
```
But, what's more, if you check your service's status with
```
sudo systemctl status minetest
```
You would see it had failed miserably. This is because systemd does not have any context, no links to worlds, textures, configuration files, or details of the specific user running the service. You can solve this problem by adding the `User` directive to your unit:
```
# minetest.service
[Unit]
Description= Minetest server
Documentation= https://wiki.minetest.net/Main_Page
[Service]
Type= simple
User= <username>
ExecStart= /usr/games/minetest --server
ExecStartPost= /home/<username>/bin/mtsendmail.sh "Ready to rumble?"
  "Minetest Starting up"
TimeoutStopSec= 180
ExecStop= /home/<username>/bin/mtsendmail.sh "Off to bed. Nightie night!"
  "Minetest Stopping in 2 minutes"
ExecStop= /bin/sleep 120
ExecStop= /bin/kill -2 $MAINPID
```
The `User` directive tells systemd which user's environment it should use to correctly run the service. You could use root, but that would probably be a security hazard. You could also use your personal user and that would be a bit better, but what many administrators do is create a specific user for each service, effectively isolating the service from the rest of the system and users.
The next step is to make your service start when you boot up and stop when you power down your computer. To do that you need to _enable_ your service, but, before you can do that, you have to tell systemd where to _install_ it.
In systemd parlance, _installing_ means telling systemd when in the boot sequence should your service become activated. For example the _cups.service_ , the service for the _Common UNIX Printing System_ , will have to be brought up after the network framework is activated, but before any other printing services are enabled. Likewise, the _minetest.service_ uses a user's email (among other things) and will have to be slotted in when the network is up and services for regular users become available.
You do all that by adding a new section and directive to your unit:
```
...
[Install]
WantedBy= multi-user.target
```
You can read this as "wait until we have everything ready for a multiples user system." Targets in systemd are like the old run levels and can be used to put your machine into one state or another, or, like here, to tell your service to wait until a certain state has been reached.
Your final _minetest.service_ file will look like this:
```
# minetest.service
[Unit]
Description= Minetest server
Documentation= https://wiki.minetest.net/Main_Page
[Service]
Type= simple
User= <username>
ExecStart= /usr/games/minetest --server
ExecStartPost= /home/<username>/bin/mtsendmail.sh "Ready to rumble?"
  "Minetest Starting up"
TimeoutStopSec= 180
ExecStop= /home/<username>/bin/mtsendmail.sh "Off to bed. Nightie night!"
  "Minetest Stopping in 2 minutes"
ExecStop= /bin/sleep 120
ExecStop= /bin/kill -2 $MAINPID
[Install]
WantedBy= multi-user.target
```
Before trying it out, you may have to do some adjustments to your email script:
```
#!/bin/bash
# mtsendmail
sleep 20
echo $1 | mutt -F /home/<username>/.muttrc -s "$2" my_minetest@mailing_list.com
sleep 10
```
This is because the system will need some time to set up the emailing system (so you wait 20 seconds) and also some time to actually send the email (so you wait 10 seconds). Notice that these are the wait times that worked for me. You may have to adjust these for your own system.
And you're done! Run:
```
sudo systemctl enable minetest
```
and the Minetest service will come online when you power up and gracefully shut down when you power off, warning your users in the process.
### Conclusion
The fact that Debian, Ubuntu, and distros of the same family have a special package called _minetest-server_ that does some of the above for you (but no messaging!) should not deter you from setting up your own customised services. In fact, the version you set up here is much more versatile and does more than Debian's default server.
Furthermore, the process described here will allow you to set up most simple servers as services, whether they are for games, web applications, or whatever. And those are the first steps towards veritable systemd guruhood.
--------------------------------------------------------------------------------
via: https://www.linux.com/blog/learn/2018/5/systemd-services-beyond-starting-and-stopping
作者：[Paul Brown][a]
选题：[lujun9972](https://github.com/lujun9972)
译者：[译者ID](https://github.com/译者ID)
校对：[校对者ID](https://github.com/校对者ID)
本文由 [LCTT](https://github.com/LCTT/TranslateProject) 原创编译，[Linux中国](https://linux.cn/) 荣誉推出
[a]:https://www.linux.com/users/bro66
[1]:https://www.linux.com/blog/learn/intro-to-linux/2018/5/writing-systemd-services-fun-and-profit
[2]:http://www.mutt.org/

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Systemd 服务：比启动停止服务更进一步
======
![](https://www.linux.com/sites/lcom/files/styles/rendered_file/public/systemd-minetest-2.jpg?itok=bXO0ggHL)
在上一篇[文章][1]中，我们展示了如何创建一个 systemd 服务并使用普通用户启动和终止游戏服务器。但到目前为止，使用这个服务并不比直接运行服务器高明多少。让我们更进一步，让其可以向玩家发邮件，包括在服务器可用时通知玩家，在服务器关闭前警告玩家：
```
# minetest.service
[Unit]
Description= Minetest server
Documentation= https://wiki.minetest.net/Main_Page
[Service]
Type= simple
ExecStart= /usr/games/minetest --server
ExecStartPost= /home/<username>/bin/mtsendmail.sh "Ready to rumble?" "Minetest Starting up"
TimeoutStopSec= 180
ExecStop= /home/<username>/bin/mtsendmail.sh "Off to bed. Nightie night!" "
  Minetest Stopping in 2 minutes"
ExecStop= /bin/sleep 120
ExecStop= /bin/kill -2 $MAINPID
```
这里涉及几个新的指令。首先是 `ExecStartPost` 指令，该指令可以在主进程启动后马上执行任何你指定的操作。在本例中，你执行了一个自定义脚本 `mtsendmail` (内容如下)，该脚本以邮件形式通知你的朋友服务器已经启动。
```
#!/bin/bash
# mtsendmail
echo $1 | mutt -F /home/<username>/.muttrc -s "$2" my_minetest@mailing_list.com
```
我们使用 [Mutt][2] 这个命令后邮件客户端发送消息。虽然从实际效果来看，上述脚本仅有 1 行，但 systemd unit 的参数中不能包含管道及重定向操作，故我们需要将其封装到脚本中。
顺便提一下，还有一个 `ExecStartPre` 指令，用于在服务主进程执行之前进行指定操作。
接下来我们看到，关闭服务器涉及了好几条指令。`TimeoutStopSec` 指令用于设置 systemd 友好关闭服务的最大等候时间，默认值大约是 90 秒。超过这个最大等候时间，systemd 会强制关闭服务并报错。考虑到你希望在彻底关闭服务器前给用户预留几分钟的时间，你需要将超时时间提高至 3 分钟，这样 systemd 就不会误认为服务关闭时出现问题。
接下来是关闭服务的具体指令部分。虽然没有 `ExecStopPre` 这样的指令，但你可以通过多次使用 `ExecStop` 指令实现关闭服务器前执行操作的目标。多个 `ExecStop` 指令按从上到下的顺序依次运行，这样你就可以在服务器真正关闭前向用户发送消息。
通过这个特性，你首先应该向你的朋友发邮件，警告其服务器即将关闭，然后等待两分钟，最后关闭服务器。可以使用 [Ctrl] + [c] 关闭 Minetest 服务器，该操作会被转换为一个中断信号 ( _SIGINT_ )；当你执行 `kill -2 $MAINPID` 时就会发送该中断信号，其中 `$MAINPID` 是 systemd 变量，用于记录你服务中主进程的 PID 信息。
看上去好多了！如果你此时启动服务，
```
systemctl --user start minetest
```
服务会启动 Minetest 服务器并向你的用户发送邮件。关闭服务的情形基本类似，只不过会额外留给用户 2 分钟时间退出登录。
### 开机自启动
下一步我们让你的服务在主机启动后立即可用，在主机关闭时自动关闭。
我们需要将你的服务文件移动到系统服务目录，即 _/etc/systemd/system/_：
```
sudo mv /home/<username>/.config/systemd/user/minetest.service /etc/systemd/system/
```
如果你希望此时启动该服务，你需要拥有超级用户权限：
```
sudo systemctl start minetest
```
另外，可以使用如下命令检查服务状态：
```
sudo systemctl status minetest
```
你会发现服务很糟糕地处于失败状态，这是因为 systemd 不能通过上下文信息、特征、配置文件得知具体使用哪个用户运行该服务。在 unit 文件中增加 `User` 指令可以解决这个问题。
```
# minetest.service
[Unit]
Description= Minetest server
Documentation= https://wiki.minetest.net/Main_Page
[Service]
Type= simple
User= <username>
ExecStart= /usr/games/minetest --server
ExecStartPost= /home/<username>/bin/mtsendmail.sh "Ready to rumble?"
  "Minetest Starting up"
TimeoutStopSec= 180
ExecStop= /home/<username>/bin/mtsendmail.sh "Off to bed. Nightie night!"
  "Minetest Stopping in 2 minutes"
ExecStop= /bin/sleep 120
ExecStop= /bin/kill -2 $MAINPID
```
systemd 从 `User` 指令中得知应使用哪个用户的环境变量来正确运行该服务。你可以使用 root 用户，但这可能产生安全风险；使用你的个人用户会好一些，但不少管理员的做法是为服务单独创建一个用户，这样可以有效地将服务与其它用户和系统组件相互隔离。
下一步我们让你的服务在系统启动时自动启动，系统关闭时自动关闭。要达到这个目的，你需要 _enable_ 你的服务；但在这之前，你还需要告知 systemd 从哪里 _install_。
对于 systemd 而言，_installing_ 告知 systemd 在系统启动的具体哪个步骤激活你的服务。以 _通用 Unix 打印系统_ _cups.service_ 为例，它的启动在网络框架启动之后、其它打印服务启动之前。又如，_minetest.server_ 需要使用用户邮件（及其它组件），需要等待网络和普通用户对应的服务就绪后才可启动。
你只需要在 unit 中添加一个新段和新指令：
```
...
[Install]
WantedBy= multi-user.target
```
你可以将其理解为“等待多用户系统的全部内容就绪”。systemd 中的 targets 类似于旧系统中的 run levels，可以用于将主机转移到一个或另一个状态，也可以像本例中这样让你的服务等待指定状态出现后运行。
你的最终 _minetest.service_ 文件如下：
```
# minetest.service
[Unit]
Description= Minetest server
Documentation= https://wiki.minetest.net/Main_Page
[Service]
Type= simple
User= <username>
ExecStart= /usr/games/minetest --server
ExecStartPost= /home/<username>/bin/mtsendmail.sh "Ready to rumble?"
  "Minetest Starting up"
TimeoutStopSec= 180
ExecStop= /home/<username>/bin/mtsendmail.sh "Off to bed. Nightie night!"
  "Minetest Stopping in 2 minutes"
ExecStop= /bin/sleep 120
ExecStop= /bin/kill -2 $MAINPID
[Install]
WantedBy= multi-user.target
```
在尝试新的服务之前，你还需要对邮件脚本做一些调整：
```
#!/bin/bash
# mtsendmail
sleep 20
echo $1 | mutt -F /home/<username>/.muttrc -s "$2" my_minetest@mailing_list.com
sleep 10
```
这是因为系统需要一定的时间启动邮件系统（这里等待 20 秒），也需要一定时间完成邮件发送（这里等待 10 秒）。注意脚本中的等待时间数值适用于我的系统，你可能需要针对你的系统调整数值。
大功告成啦。执行如下操作：
```
sudo systemctl enable minetest
```
你的 Minetest 服务将在系统启动时自动启动，在系统关闭时友好关闭并通知你的用户。
### 总结
事实上 Debian, Ubuntu 和一些族类的发行版提供了 _minetest-server_ 这个特别的软件包，可以提供一部分上述功能，（但不包括邮件通知功能）。即使如此，你还是可以建立你独有的自定义服务；事实上，你目前建立的服务比 Debian 默认提供的服务更加通用，可以提供更多功能。
更进一步的说，我们这里描述的流程可以让你将大多数简单服务器转换为服务，类型可以是游戏、网站应用或其它应用。同时，这也是你名副其实地踏入 systemd 大师殿堂的第一步。
--------------------------------------------------------------------------------
via: https://www.linux.com/blog/learn/2018/5/systemd-services-beyond-starting-and-stopping
作者：[Paul Brown][a]
选题：[lujun9972](https://github.com/lujun9972)
译者：[pinewall](https://github.com/pinewall)
校对：[校对者ID](https://github.com/校对者ID)
本文由 [LCTT](https://github.com/LCTT/TranslateProject) 原创编译，[Linux中国](https://linux.cn/) 荣誉推出
[a]:https://www.linux.com/users/bro66
[1]:https://www.linux.com/blog/learn/intro-to-linux/2018/5/writing-systemd-services-fun-and-profit
[2]:http://www.mutt.org/