code: def fetch_job(self, job_id, checkout=False):
          
          self.job_id = job_id
  
          self.logger.debug("Git fetch job reference %s" % (self.ref_head, ))
          out, code, err = self.command_exec(['ls-remote', 'origin', self.ref_head])
  
          if code:
              self.logger.error('Could not find the job ' + job_id + ' on the server. Are you online and does the job exist?')
              sys.exit(1)
  
          try:
              self.command_exec(['fetch', '-f', '-n', 'origin', self.ref_head+':'+self.ref_head])
          except Exception:
              self.logger.error("Could not load job information for " + job_id + '. You need to be online to start pre-configured jobs.')
              raise
  
          self.read_job(job_id, checkout)
docs: Fetch the current job reference (refs/aetros/job/<id>) from origin and (when checkout=True)read its tree to
          the current git index and checkout into working director.