The simplest way to go about this is not to try to test the validity of an applicant's claims to experience. Instead, I recommend you use the opportunity to get clear on what extent of directly relevant claimed experience the applicant has, and then go into more detail about specific problems they have handled before (effectively exploring stories of experience). This isn't perfect, as not all applicants are prepared to talk about their prior work problems in this way, but it has become so generally accepted as an interview strategy that not being able to talk about your work in this way would be considered a bad sign anyway.
In the context of your particular case, I'd suggest a line of questioning along these lines:
- "Have you administered servers before?"
- "Tell me about that experience - how many servers were there, what were they used for, etc?"
- "Who was responsible for the server on a day-to-day basis? Did you set them up, configure them, repair/replace them? Software configuration, networking?"
- "Can you tell me about a time you had to deal with a problem with the servers, especially one that was challenging? Tell me about how you diagnosed it...mitigated it...solved it..."
The goal is not to test them on their knowledge, but rather to specifically map out what experience they are supposed to have, without the need to verify it with some kind of test. Specifics are key. "I was a server administrator" is easy to say on a resume, but when you push for details does that mean they were basically running a server cluster for their last company or they once figured out how to host a website on their laptop?
In 9/10 cases, I've found that I learned all I needed to know from these conversations, because you get the story of what they really claim to have done and been responsible for. And as you get into the details, most people aren't clever enough to have invented detailed stories of problems and solutions out of nowhere.
I also found that a lot of title/brand name inflation disappears at this stage. Someone working in a famous neuroscience lab turns out to have been responsible for putting the caps on people or handling phone calls, someone who had a job for a famous company's machine learning division just hand-labeled images (image tagging), or a new student has had one class in Java so they were told to put it down as a skill because they are willing to learn it. Sometimes this is great and these are the honest people you want to hire - sometimes it just means they aren't right for the current position.
If you find someone who seems to talk the talk and claims to have the experience you care about and think of moving forward with hiring, then that is a great time to identify or recruit someone who already has the skills you want to hire to talk with the candidate in a second interview. Unfortunately the majority of people with technical skills don't also have any experience in interviewing. But how to conduct in-depth technical interviews is a separate question entirely :)
In summary, don't try even try to test a candidate in the first interview, because it is far more important you get the full story on what experience they claim to have and how they obtained that experience. This is where you throw away job titles and companies they've worked for and find out what they say they really did in their job - what they worked with, what level of responsibility they had, scale, what the specific technologies were, etc. This information should be noted by you, and then it perfectly sets up an in-depth technical interview with people who have the skills you are hiring for so they can better determine if this candidate is one who should get an offer (or I guess yet another interview). This could technically be an interview with you, or stage 2 of the same interview - but I've never found I had time for that on a first interview. You have more important things to determine at this stage, which helps to take the stress off both you and the candidate and focus on learning about if this might potentially be a good fit - rather than trying to seal the deal in one go.