Some script that i found online to stop all jenkins builds at once

stop_builds.groovy

import jenkins.model.Jenkins

def numCancels = 0;
Jenkins.instance.getAllItems(Job.class).each{ 
  def job = it
  for (build in job.builds) {
    if (build.isBuilding()) { 
      build.doStop()
      numCancels++
     }
  }  
}

println("${numCancels}");