I wonder how should I review questions like this one - apparently the OP did solve his own question but didn't post an answer, but rather included the answer in the question part. I am not sure if the solution the user came up with is actually valid, so I don't want to post an answer myself. There is no (for all I see) 'not-a-question' flag. Am I just to comment on the question with a suggestion that the user should post an answer?
When the author of a question edits the question to add a link to another question on Ask Ubuntu that solved the problem, usually the proper response is to close their question as a duplicate of that question. That's the best thing to do in that particular case.
At 3000 reputation, users can cast close (and reopen) votes. Before that, users with at least 15 reputation (which includes everyone who can use the review system) can flag questions for closure by clicking the flag link followed by "it doesn't belong here, or it is a duplicate...".
Flagging a post, voting to close it, commenting, editing the post, or any combination of those and some other actions (like voting up or down) are sufficient to enable you to click the I'm Done button in the review system. In this case, voting or flagging to close is sufficient. When 3k+ rep users vote to close, they automatically post a comment about the possible duplicate. You might consider posting a comment manually while flagging to close if you think it would be helpful; in this situation, I could go either way.
When the solution isn't to close the question:
There's a more general meta-question here: what should we do when an OP edits or comments on their question to indicate the solution, and the solution hasn't been posted?
If they're not merely indicating another question where the problem was solved (as in this case), then you have two options:
- Comment to explain that they should post the answer.
- Post the answer yourself. You can quote from what they said. You should make sure any quoted text is properly attributed, of course. If you feel that the answer you're posting shouldn't be considered your own work, you might decide to make it community wiki. But that is not actually required.
Some people think it's important to comment first, to give the OP a change to post their answer. They point out that it's best for the OP to post it, that this way people other than the OP don't have to do the work, and that this way the OP has a better chance to learn how to use the system and that it's good for them to have a chance to get rep from their answer.
Others think none of that is as important as getting an answer posted once one is available, and that it's usually best to just post a community wiki answer with the solution, rather than wait to see if the OP ever does.
I am strictly in the second camp: I think that if you have an answer to a question, you should almost always post it for the benefit of people who find the question. I only tell OP's to post the answer themselves if I think they'd do a better job, or if I know they are actively checking the site (and thus would see my comment and likely act on it by posting an answer).
But really, either approach is just fine. The important thing is that you do something to move the question's status along, so that people don't become confused as to whether or not it is answered, and so that other people with the same problem are able to find the answer without too much trouble. This "library of detailed answers" needs answers, after all...
When the solution isn't really a solution:
Sometimes the OP will post something that gets part of the way to a solution, but they still need help. Sometimes this is totally clear; other times, editing can help to clarify that. In these circumstances, no answer generally has to be posted, and nobody should be encouraged to post one unless they can solve the problem.
Other times, an OP will post something like "the problem went away by itself, I don't know how." In these situations, provided that there are no other answers that might be helpful to anyone, the post should be closed. These days, we're using the off-topic close reason for those posts; there's a special sub-reason just for that situation.