Jenkins Master-Slave: Key exchange was not finished, connection is closed - jenkins

Question

I want to connect a slave to Master-Jenkins, but when trying to connect i'm getting following Error:
[05/02/18 15:26:59] [SSH] Opening SSH connection to <IP>
Key exchange was not finished, connection is closed.
java.io.IOException: There was a problem while connecting to <IP>:22
at com.trilead.ssh2.Connection.connect(Connection.java:818)
at hudson.plugins.sshslaves.SSHLauncher.openConnection(SSHLauncher.java:1324)
at hudson.plugins.sshslaves.SSHLauncher$2.call(SSHLauncher.java:831)
at hudson.plugins.sshslaves.SSHLauncher$2.call(SSHLauncher.java:820)
at java.util.concurrent.FutureTask.run(FutureTask.java:266)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
at java.lang.Thread.run(Thread.java:748)
Caused by: java.io.IOException: Key exchange was not finished, connection is closed.
at com.trilead.ssh2.transport.KexManager.getOrWaitForConnectionInfo(KexManager.java:93)
at com.trilead.ssh2.transport.TransportManager.getConnectionInfo(TransportManager.java:230)
at com.trilead.ssh2.Connection.connect(Connection.java:770)
... 7 more
Caused by: java.io.IOException: Cannot negotiate, proposals do not match.
at com.trilead.ssh2.transport.KexManager.handleMessage(KexManager.java:405)
at com.trilead.ssh2.transport.TransportManager.receiveLoop(TransportManager.java:777)
at com.trilead.ssh2.transport.TransportManager$1.run(TransportManager.java:489)
... 1 more
[05/02/18 15:26:59] Launch failed - cleaning up connection
[05/02/18 15:26:59] [SSH] Connection closed.
Configuration for Node:
- Start-Method: Start Slave over SSH
- Hostname: is the IP
- Access Data: user i created for SSH Access - > public key is in authorized keys on Slave Node
If i am on my Master as user "jenkins" and do a ssh jenkins#<IP> i can login wihtout problems (public key is on slave).
Why it doesn't work for "UI-Jenkins".
Jenkins-Version: 1.658
Node: Ubuntu 14.04
SSH-Slave Plugin: 1.26

Answer 1

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 "
Jenkins master fails to connect to the slave over SSH

Answer 2

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.

Answer 3

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'

Answer 4

Just recently run into this issue with docker
Find the Java Path
/home/jenkins # which java
/opt/java/openjdk/bin/java
Export the Java Path. In this case I am using the docker-compose
...
exp_agent:
image: jenkins/ssh-agent:alpine
restart: always
environment:
JENKINS_AGENT_SSH_PUBKEY: $ENV_JENKINS_AGENT_SSH_PUBKEY
JAVA_HOME: $ENV_JAVA_HOME
container_name: jenkins-ssh-agent
ports:
- 22:22
networks:
- jenkins
...
The master still complains about the path of Java as /opt/java/openjdk/bin/java is not among the expected paths
...
[12/04/21 11:44:07] [SSH] Checking java version of /usr/bin/java
...
Create a symbolic link between the java path and one of the expected paths in the docker container (This could be automated in a Dockerfile)
ln -s /opt/java/openjdk/bin/java /usr/bin/java