feature: support different versions of systemd

[pires]

For instance, in RHEL7 (systemd 219), user-mode systemd doesn't seem to be a thing. Also, certain unit attributes we populate today are unsupported, such as:

• BindReadOnlyPaths
• PrivateMounts
• ReadOnlyPaths
• TemporaryFileSystem

I understand older distros may not be a goal but if we want this project to be used on bigger companies, we'll have to account for this.

[miekg]

I think most of these are not essential, so we can live without if we detect older systemds. The ReadOnly* ones are nice to have though.

OTOH, even I have access to RHEL8 machines...

[pires]

The hard part is to find a feature matrix to determine what attributes are available per version. If we had that, it would be easy to implement this. I need to do some digging because there's demand for RHEL 7 support :)

[miekg]

Even better would be to probe for support, but harder

[pires]

I don't think systemd even does that, does it?

[miekg]

[ Quoting [email protected] in "Re: [virtual-kubelet/systemk] featu..." ]

I don't think systemd even does that, does it?

don't know. You said you got an error, is that detectable from within systemk? We could just barf out dummy units and see what happens

[pires]

I just saw these in journal logs, when parsing the unit, eg

Unknown lvalue 'PrivateMounts' in section 'Service'

[miekg]

[ Quoting [email protected] in "Re: [virtual-kubelet/systemk] featu..." ]

I just saw these in journal logs, when parsing the unit, eg

Unknown lvalue 'PrivateUsers' in section 'Service'

ugh, silently drops it #sigh

[miekg]

[ Quoting [email protected] in "Re: [virtual-kubelet/systemk] featu..." ]

I just saw these in journal logs, when parsing the unit, eg

Unknown lvalue 'PrivateUsers' in section 'Service'

there is systemd-run which takes a unit as argument, I would assume that actually errors when giving it the wrong thing?

[miekg]

[ Quoting [email protected] in "Re: [virtual-kubelet/systemk] featu..." ]

I just saw these in journal logs, when parsing the unit, eg

Unknown lvalue 'PrivateUsers' in section 'Service'

% systemd-run -p PublicTmp=no ls Unknown assignment: PublicTmp=no % echo $? 1

[pires]

If the CLI does it, then maybe there's an API behind it? I'm not supportive of wrapping CLI because that's not a contract I trust in.

[miekg]

Maybe? Doesn't matter for our API as we can swap it later. Getting some means of detecting and making that code easy and elegant is my goal for now

On Fri, 22 Jan 2021, 18:22 Pires, [email protected] wrote:

If the CLI does it, then maybe there's an API behind it? I'm not supportive of wrapping CLI because that's not a contract I trust in.

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[miekg]

Regardless how we probe: this is what I had in mind: https://github.com/virtual-kubelet/systemk/pull/74