title: Run Jenkins jobs on Linux under a User
body: <p>I have Jenkins installed in Linux and I want to run the build(s) under a user.</p>
  
  <p>Not just a simple user, but one that belongs to the list of user that access the linux machine and that belongs to a certain group as it has privileges to modify/create files under a certain folder.</p>
  
  <p>I have read somewhere that you can set the variable $JENKINS_USER but I do not know where and how.
   Thank you for your time</p>
  
  <p>P.S. I did some research all the questions posted are similar but not the same as this one</p>
  
  <p>Please if I am not clear read this:
  Usually Jenkins execute the build using a user called jenkins, now I want to be able to use a different user (pre-existing).</p>