Jenkins Master-Slave: Key exchange was not finished, connection is closed
That "solved" the issue:
"Workaround is by commenting out MACs and KexAlgorithm line in /etc/ssh/sshd_config of Jenkins Slave and restarting the sshd (service ssh restart on Ubuntu)
UPDATE: the issue has been resolved as of 2017-04-29 "
Execute this command on destination node.
sudo -i su -c 'sed -i -e "s/MACs /MACs hmac-sha1,/g" /etc/ssh/sshd_config; service sshd restart'
Thought I'd throw my experience in this thread: my environment had a Windows master and mixed Windows and Linux agents. One Windows agent refused to connect to master, even after Master pushed 'jenkins-agent' and the other supporting files to the agent.
This agent had 6 different versions of the JDK and JRE installed. I uninstalled all of them, reinstalled only the latest JDK we needed, and set JAVA_HOME. This fixed the connectivity issue.