Bug 30053

Summary:	expand unset environment variables to nothing
Product:	systemd	Reporter:	Dave Reisner <d>
Component:	general	Assignee:	Lennart Poettering <lennart>
Status:	RESOLVED FIXED	QA Contact:
Severity:	normal
Priority:	medium	CC:	marti
Version:	unspecified
Hardware:	All
OS:	Linux (All)
Whiteboard:
i915 platform:		i915 features:
Attachments:	Strips quotes in variables read from EnvironmentFile

Description Dave Reisner 2010-09-06 15:04:59 UTC

Systemd should follow the shell's default behavior of expanding nonexistent environment variables to nothing, within the context of a .service file (e.g. ExecStart).

Rationale: I have a daemon which sources an EnvironmentFile. The EnvironmentFile defines a variable which isn't required for normal behavior but which, if set, needs to be passed as a startup parameter in ExecStart. For example:

[Service]
...
EnvironmentFile=/etc/conf.d/sshd
ExecStart=/usr/sbin/sshd -D $SSHD_ARGS
...


If SSHD_ARGS is unset, it appears to be passed to /usr/sbin/sshd literally which then fails to start. This would be alleviated if systemd were to expand unset environment variables to a null string.

Comment 1 Dave Reisner 2010-09-06 17:28:18 UTC

I think I may be misunderstanding the way the ExecStart command is being handled. Is there no environment variable expansion at all?

Comment 2 Lennart Poettering 2010-09-07 04:27:12 UTC

There is env var expansion, in two syntaxes:

$foo as a single word will be replaced by the contents of $foo split up at whitespaces as several arguments. And ${foo} may appear as part of another word (or seperately) and will be replaced by the contents for $foo, but not split up.

Note however that env var expansion is (currently) not supported on the binary path itself, only on its contents.

Comment 3 Dave Reisner 2010-09-07 11:03:31 UTC

Created attachment 38523 [details] [review]
Strips quotes in variables read from EnvironmentFile

Comment 4 Dave Reisner 2010-09-07 11:03:41 UTC

Ok, I've narrowed this down to an issue with quoting. In the EnvironmentFile in question, I have:

SSHD_ARGS=""

...which is interpreted literally as "". I've attached a patch which fixes this, but it takes a sledgehammer approach to a 10 cent nail. the unquote() function in util.c is probably a better choice, but it doesn't appear to work as I'd like it to (I'm unsure of the behavior of strdup when its passed an empty string).

Comment 5 Lennart Poettering 2011-01-20 15:24:46 UTC

This is fixed in v16.

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