Xvfb-

root@ubuntu:/# systemctl status  Openvmi-Xvfb-Manger.service 
* Openvmi-Xvfb-Manger.service - Openvmi Xvfb Manger
   Loaded: loaded (/lib/systemd/system/Openvmi-Xvfb-Manger.service; enabled; ven
dor preset: enabled)
   Active: inactive (dead)

root@ubuntu:/# find ./ -name  Openvmi-Xvfb-Manger.service
./lib/systemd/system/Openvmi-Xvfb-Manger.service
./etc/systemd/system/multi-user.target.wants/Openvmi-Xvfb-Manger.service

 优先级
systemd的使用大幅提高了系统服务的运行效率, 而unit的文件位置一般主要有三个目录：


Table 1.  Load path when running in system mode (--system).
┌────────────────────────┬─────────────────────────────┐
│Path                    │ Description                 │
├────────────────────────┼─────────────────────────────┤
│/etc/systemd/system     │ Local configuration         │
├────────────────────────┼─────────────────────────────┤
│/run/systemd/system     │ Runtime units               │
├────────────────────────┼─────────────────────────────┤
│/lib/systemd/system     │ Units of installed packages │
└────────────────────────┴─────────────────────────────┘
这三个目录的配置文件优先级依次从高到低，如果同一选项三个地方都配置了，优先级高的会覆盖优先级低的

PS：使用命令 systemctl is-enabled postfix.service 得到的值可以是enable、disable或static，这里的 static 它是指对应的 Unit 文件中没有定义[Install]区域，因此无法配置为开机启动服务。 

a template for multiple Xvfb services
Simple xvfb.service systemd unit files for xvfb can be found at https://www.centos.org/forums/viewtopic.php?f=48&t=49080#p208363 and at https://askubuntu.com/a/621256/43344 . However, as I mentioned at the latter one can also take a templatized approach:

[Unit]
Description=virtual frame buffer X server for display %I
After=network.target

[Service]
ExecStart=/usr/bin/Xvfb %I -screen 0 1280x1024x24

[Install]
WantedBy=multi-user.target
As a locally-written, non-system non-packaged, unit file for system-wide (as opposed to per-user) services this goes into /etc/systemd/system/xvfb@.service of course.

controlling the services
One instantiates the template, into an actual named service, with the display number that is desired. For display :99, therefore, there is an actual service instance named xvfb@:99.service.

Set the service to auto-start on bootstrap with systemctl enable xvfb@:99.service .
Unset auto-starting the service with systemctl disable xvfb@:99.service .
Start the service manually with systemctl start xvfb@:99.service .
Stop the service manually with systemctl stop xvfb@:99.service .
Inspect the current service status in detail with systemctl status xvfb@:99.service .