Found by being asked whether processes and containers handle environment the
same way. They do not, and the difference is not cosmetic.
Docker passes --env through literally. A unit file reads three things out of a
value that nothing else does, and a module's environment routinely contains all
three because a generated password is arbitrary bytes:
- % begins a specifier. %H is the hostname. A password containing one is
silently replaced, and it fails later as an authentication error nobody can
explain by reading the declaration.
- whitespace separates assignments. Unquoted, K=a b sets K to "a" and reads
"b" as another assignment.
- a newline ends the line, and what follows is read as a unit DIRECTIVE.
The first two are escaped: quoted, with quotes and backslashes escaped and
percent doubled. The third cannot be — a unit's environment has no way to carry
a line break — so it is refused in validation, near whoever wrote it. Without
that, an environment value could write ExecStart= and have the machine run
something nobody declared.
Ordinary awkward values stay accepted, because refusing those too would leave a
module unable to hold a generated password.
Claude-Session: https://claude.ai/code/session_01D6qtiYU3P9jk3pnAXyAFyx
jschoubben
de5160de4a