It takes a lot of effort and money to enforce copyleft open source licenses, a lot of companies just violate them regardless. Some companies even violate permissive licenses, for eg my router violates the microhttpd BSD license.
The latest GPL lawsuit I saw was only possible due to a large grant from amateur radio hobbyists.
Offer two licenses. One GPL and the other commercial. Make the commercial license as costly as possible, even Oracle grade by charging per core. Include language stating that the licensing agreement falls back to the commercial license if the GPL is violated and the violation is not remedied according to the provisions set in the GPL.
Any licensing fees collected get poured back into the open source project.
If another company is stupid enough to ignore these terms, I'm sure you can find someone willing to sue on your behalf for a fraction of the damages owed to you.
Is there an easy way of providing commercial licences? Has anybody had experiences with this?
I've seen Super Source (https://supso.org/), which I think used to be called Supported Source (https://supportedsource.org). It seems to make providing commercial licenses easy. But their website is pretty bare. Do people usually just roll their own with Square or Stripe? I've found it hard to get search results on this at all.
If somebody is going to be paying you more than $1000, they'll contact you about it. You don't need to automate the license payments; you just need to check your email.
Most GPL projects aim for a diverse copyright holder base, with the code solely licensed under the GPL, so that no one entity can escape their GPL obligations by paying money. In that scenario it becomes harder to enforce the GPL, unless you have a principled copyright holder base with deep pockets. Hopefully the Software Freedom Conservancy lawsuit mentioned upthread will change that, they aim to set the precedent that anyone who receives GPL violating binaries can file GPL violation lawsuits.
Even so, I'd assume that a company that knowingly infringes on the GPL is much less likely to demand free support, lest they draw attention to their violation. So at the very least it should free maintainers from having to deal with bug reports/feature requests/entitled demands from corporate entities that refuse to give back.
None of the Apache PLC4X users asking for free support on behalf of their companies mentioned the company name nor used a company email address. I expect it would be pretty easy to keep the gratis support requests and GPL violations fairly separate.
The latest GPL lawsuit I saw was only possible due to a large grant from amateur radio hobbyists.
https://sfconservancy.org/copyleft-compliance/vizio.html https://sfconservancy.org/press/qanda.html