**NOTE**:

Judging from the comments and votes, it appears that my answer is being misinterpreted. Let me make it easy and spell it out:

<!-- language: python -->

    import discretion
    import question

    if question.OP_using_Ubuntu() and "Mint" in question.text():
       question.vote_remain_open()

    else if not question.OP_using_Ubuntu:
       if question.not_specific_to_other_OS():   
           question.vote_remain_open()

    else:
       question.close()



***
The simple question that I personally ask is this: "Is the issue specific to whatever Ubuntu-based/Debian-based OS in question?" (note the "-based" part). If yes, it's a sure sign to close as off-topic.  In cases such as traversing directory tree, shell scripting, renaming files, moving files, and other things which have no relation to the underlying workings of the operating system - in those cases the question is well applicable to Ubuntu, in many cases can be voted as duplicate, and as Kaz said in those cases mention of another OS can be removed altogether.

Different story arises with OS X, FreeBSD, RHEL, and CentOS - they have different package managers, OS X has different directory tree structure, and utilities/commands have options that are missing or behave differently. As such, solution that may well work for Ubuntu && Mint && Debian && Elementary, won't work for those OS.

There's really no silver bullet to this problem and it comes up over and over again, and when I had just around 1k reputation I've been hastily closing things myself. From experience, I can tell the solution is  for people to start reading questions and use discretion, focus on quality over quantity, and start actually caring about proper close-voting.