To keep jenkins running in the background you can use screen
.
#!/bin/bash
# jenkins.sh
if ! pgrep "jenkins" > /dev/null; then
screen -dm java -Xms256m -Xmx512m -Dhudson.udp=-1 -Dhudson.DNSMultiCast$
fi
*/2 * * * * /usr/local/bin/bash /usr/home/YOUR_USER/domains/jenkins.example.com/jenkins.sh >/dev/null 2>&1 # Jenkins Cron