阻止服务启动

Question

想法是创建一个永远不会启动的 keep-down.service：

[Unit]
Description=Keeps daemon down

Before=mydaemon.service
ConditionPathIsDirectory=/var/lib/dummy-never-existing-path

[Service]
ExecStart=/bin/true

[Install]
WantedBy=multi-user.target

所以 mydaemon.service 需要它。安装 keep-down.service 时，mydaemon.service 无法启动（理论上）。

动机：

没有systemctl命令可以启动mydaemon.service
mydaemon.service 单元文件没有修改
不要弄乱 mydaemon.service
它是原子的：installing/removing keep-down.service 自定义包

问题是 mydaemon.service 无论如何都会启动。这是为什么？

Answer 1

您已指定 keep-down 服务必须在之前启动 mydaemon.service:

Before=mydaemon.service

但是你实际上并没有配置两者之间的任何依赖关系，比如：

RequiredBy=mydaemon.service

详细信息在 systemd.unit 手册页中，例如关于 Before= 和 After=:

Note that this setting is independent of and orthogonal to the requirement dependencies as configured by Requires=. It is a common pattern to include a unit name in both the After= and Requires= option, in which case the unit listed will be started before the unit that is configured with these options.

然而，这一切实在是大可不必。您可以使用 systemctl mask 命令完成您想要的操作：

   mask NAME...
       Mask one or more unit files, as specified on the command line. This
       will link these units to /dev/null, making it impossible to start
       them. This is a stronger version of disable, since it prohibits all
       kinds of activation of the unit, including enablement and manual
       activation. Use this option with care. This honors the --runtime
       option to only mask temporarily until the next reboot of the
       system. The --now option can be used to ensure that the units are
       also stopped.

所以：

# systemctl mask mydaemon

阻止服务启动

Prevent service from starting

linux

systemd