I\'m using a EC2 server instance. Used the following to install Jenkins:
wget -q -O - http://pkg.jenkins-ci.org/debian/jenkins-ci.org.key | sudo apt-key add
After Jenkins is installed just run sudo cat /var/lib/jenkins/secrets/initialAdminPassword.
sudo cat /var/lib/jenkins/secrets/initialAdminPassword
In the Jenkins login page:
User: admin Password: the output from the above command