I'm now doing my internship in a government company (in India) and I've been assigned a project to create an online forum for the company..
I'm about to use phpBB forum software to create it, which is licensed under GPL. The created forum will later be put online in the company's website.
Now my question is, does the government need to release the modified source code? Does it have to be definitely licensed under GPL ?
The GPL licence does not requires you to publish the modifications. It only requires that if you provide the software to someone, you should provide him the source code and the right to distribute it.
I suppose that you will use the code internally only (which applies even if you have external user, you don't distribute them the software, so you don't have to publish your source code)
But if you release the modified version to the public in some way, the GPL requires you to make the modified source code available to the program's users, under the GPL.
Thus, the GPL gives permission to release the modified program in certain ways, and not in other ways; but the decision of whether to release it is up to you.
Source : https://www.gnu.org/licenses/gpl-faq.en.html#GPLRequireSourcePostedPublic
Besides those legal aspects, generally governments are friendly with open-source, so if you create module that has value for the community, it might be nice to see whether your are allowed to distribute it (under the GPL licence of course).
If you are an intern, that question is not one that you should even try to answer. Your boss should be made aware that you want to use this GPL licensed software, and he needs to agree with it. If he agrees, you are fine. If he doesn't agree, don't use the GPL licensed software. If using the software forces your boss to do something that he doesn't want to do, you are in trouble.
As an example, if your boss has the excellent idea to share this software with another government company to save cost, there are legal consequences that he needs to be aware of. (Legal implication that you need to be aware of: You can distribute modified GPL software in two ways. By giving a promise to anyone on earth to give them a copy of the source code when requested, or by distributing the code together with the source code. So the boss would need to know this and likely chose distribution accompanied by source code, which means there are no further legal obligations at all).
If you run the code on your own servers without distributing it, you don't have to release your source code. If you distribute your code which links to the GPL code, then you must release your source code. If you distribute any modified GPL code, you have to release the modifications, even if your code does not link to it.
Technically I think this means that if you use a hosting company, you are bound to distribute the source code to them when you install your code. Since PHP isn't compiled, this should just happen naturally.
What's linking? PHP (like Java) isn't statically linked, so the FSF defines linking as one piece of code directly accessing another on the same (virtual or physical) machine - like a procedure call or using a public variable. Merely distributing two unrelated pieces of code on the same CD or in the same zip file does not constitute linking. Merely starting a program is not linking.
IANAL and this is not legal advice, but rather my best guess.
