在 Systemd 中引用其他环境变量

Question

在systemd中设置新环境变量时是否可以引用其他环境变量？

[Service]
EnvironmentFile=/etc/environment
Environment=HOSTNAME=$COREOS_PRIVATE_IPV4
Environment=IP=$COREOS_PRIVATE_IPV4
Environment=FELIX_FELIXHOSTNAME=$COREOS_PRIVATE_IPV4

上面的代码似乎不起作用。

Answer 1

这真的是 unix & linux 的问题。但是尽管如此：No，systemd不会在Environment=内部进行环境变量扩展。来自 man systemd.exec:

   Environment=
       Sets environment variables for executed processes. Takes a space-separated list of variable assignments. This
       option may be specified more than once, in which case all listed variables will be set. If the same variable is
       set twice, the later setting will override the earlier setting. If the empty string is assigned to this option,
       the list of environment variables is reset, all prior assignments have no effect. Variable expansion is not
       performed inside the strings, however, specifier expansion is possible. The $ character has no special meaning.
       If you need to assign a value containing spaces to a variable, use double quotes (") for the assignment.

       Example:

           Environment="VAR1=word1 word2" VAR2=word3 "VAR3=$word 5 6"

       gives three variables "VAR1", "VAR2", "VAR3" with the values "word1 word2", "word3", "$word 5 6".

正如您从文档中的示例中看到的那样 $word 只是意味着 $word 不会执行任何扩展。 man 谈论的 说明符 是 %i、%n、%u 等。它们在 man systemd.unit（在他们自己的 man 部分）。

另一方面ExecStart=及其派生将执行环境变量扩展。在 ExecStart= 上使用环境变量是 systemd 中额外环境变量的常见解决方法。我相信，这也是其中一个为什么最近有这么多程序接受来自环境和命令行参数的相同参数的原因。

ExecStart= 中的扩展示例，来自 man systemd.service：

   Example:

       Environment="ONE=one" 'TWO=two two'
       ExecStart=/bin/echo $ONE $TWO ${TWO}

   This will execute /bin/echo with four arguments: "one", "two", "two", and "two two".

   Example:

       Environment=ONE='one' "TWO='two two' too" THREE=
       ExecStart=/bin/echo ${ONE} ${TWO} ${THREE}
       ExecStart=/bin/echo $ONE $TWO $THREE

   This results in echo being called twice, the first time with arguments "'one'", "'two two' too", "", and the second
   time with arguments "one", "two two", "too".

systemd 的文档分布在多个 man 中，但一段时间后就会习惯它们。

Answer 2

在我的例子中，将系统环境变量加载到 systemd 脚本中的唯一方法是将它们加载到脚本本身中，如下所述：

https://unix.stackexchange.com/questions/146995/inherit-environment-variables-in-systemd-docker-container

# Import our environment variables from systemd
for e in $(tr "[=10=]0" "\n" < /proc/1/environ); do
        eval "export $e"
done

在 Systemd 中引用其他环境变量

Referencing Other Environment Variables in Systemd

systemd