[systemd-devel] Github systemd issue 6237

[Michael Chapman]

In Wed, 5 Jul 2017, Reindl Harald wrote:
>
>
> Am 05.07.2017 um 12:10 schrieb Michael Chapman:
>>  On Wed, 5 Jul 2017, Colin Guthrie wrote:
>> >  Reindl Harald wrote on 04/07/17 19:50:
>> > > >  When new configuration options are added, the same unit file can
>> > > >  almost always be used with older systemd, and it'll just warn & 
>> > > >  ignore
>> > > >  the parts it doesn't understand. Similarly, various configuration
>> > > >  options might be unavailable on some architectures and with some
>> > > >  compilation options. The current behaviour of warn&ignore provides
>> > > >  for "soft degradation" in those cases.
>> > > 
>> > >  frankly a new option on the left side is a completly different thing
>> > >  than a invalid value - just silently continue with invalid values of
>> > >  existing options is playing a danergous game in a crucial component 
>> > >  like
>> > >  systemd
>> > 
>> >  It's a rare thing :p but I have to agree with you here!
>> > 
>> >  I'd say if "User=-notauser" then silently failing and using root is
>> >  acceptable as per the usual semantics of "- prefix suppresses errors",
>> >  but "User=notauser" should fail IMO.
>>
>>  I'm pretty sure you'll find that it does. Specifically, it will fail when
>>  the child process for the command being executed attempts to map the
>>  username to a UID.
>>
>>  The issue being discussed here is that systemd considers "0day" to be
>>  _syntactically_ invalid for a username. See the valid_user_group_name()
>>  function in basic/user-util.c.
>
> yes and hence it should FAIL the service and not behave silently like the 
> left side of a param is unknown on a older version - a invalid VALUE in a 
> config has to fail until it's makred with a dash to silent be ignored in case 
> of errors

That's really not what the dash means.

In the various Exec*= directives, a dash means that the command is allowed 
to fail. Similarly, in WorkingDirectory= the dash means the directory need 
not exist.

I do not believe there are any cases where a dash is used to side-step 
_syntactic_ validation, nor do I think there should be.

Really, you should just think of the dashes as being part of the syntax 
for the directives that support them.

As far as directives like User= go, there _may_ be a use for dash to mean 
"do not change UIDs if the username turns out to not actually exist"... 
but I would strongly advise against it.