Question: A friend of mine who has water-treatment engineering degree recently moved to another country but struggles to find a job in his field. Because he did not want to stay at home unemployed (and because stealing food is not an option), he took a minimum-wage job (salesman in a small shop) that has nothing to do with his skills or even experience.

While I believe there is no shame for him to do that, I'm still not sure what to advise regarding his public LinkedIn profile and/or resume:

Should he mention the low-paying, unrelated job ? Is there any drawback in doing so ? Any drawback in **not** doing so ?

Answer: 
Your friend shouldn't mention the low paying, unrelated job on his Linkedin profile. The idea is to keep the Linkedin profile consistent and on point and to send a clear message through that consistency and that relevance.

Your friend can always explain himself at the interview stage. It's not about being ashamed, it's about sending a clear message about the work experience and skills set through consistency and relevance.
Avoid mentioning jobs that *may* hurt your overall job chances. Generally speaking, this is great "add-on" information that an interviewer can elicit from you("Have you ever taken a service-sector or low-paying job, to make ends meet?" - INSERT\_STORY )
.

But I would not put fast-food jobs on a page with more professional stints. 

It simply does not make sense. Again, bring it up in an interview to show your grit perhaps. But I generally don't see the point

LinkedIn, being a public "profile" , should focus on overall picture