Your perception is indeed wrong. At least with respect to the sites you mentioned:

    Site           Total Qs    Downvoted Qs    Percentage
    Ask Ubuntu  	238559	    13251             5.55
    Unix & Linux	118261      9744              8.24
    Stack Overflow	14258884    1676744           11.76
    
The table above shows<sup>1</sup> the total number of questions asked in the past month (since 20-10-2017), the number of those that have been downvoted and what percentage of the total questions have been downvoted. As you can see, this site is actually the one with the lowest percentage of downvoted questions, not the highest as you are suggesting. 

And these are the statistics of your own questions (all the questions you've asked on these sites):

    Site            Total Qs    Downvoted Qs   Percentage
    Ask Ubuntu       149            12            8.05
    Unix & Linux     66             5             7.58
    Stack Overflow   344            23            6.69
    
So yes, you do seem to have a slightly higher percentage of downvoted questions on AU, but the difference is negligible. At least with respect to U&L, anyway. But even when comparing to SO, the difference is 0.013, which can't really be called "large".

So, in conclusion, I'm afraid the numbers don't support your perception that you're being downvoted significantly more here than on other sites.  

-----

<sup>1</sup> <sub>I used these two data.se queries to get the numbers:
 [Total Questions][1], [Downvoted Questions][2]. </sub>


  [1]: http://data.stackexchange.com/unix/query/760878/total-questions
  [2]: http://data.stackexchange.com/unix/query/760878/downvoted-questions