Slave Jenkins on an RHEL box

[Peter Berghold]

I have Jenkins running merrily on an Ubuntu box and want to set up a slave on an RHEL box. 

Created a script on the RHEL box that essentially launches a script that in turn launches the slave.jar.  Trying to invoke it over SSH and there's where things take a turn for the worse.

I'm getting this:

[11/14/16 16:22:37] Launching agent
$ /usr/share/tomcat8/startSlave0
Host key verification failed.
ERROR: Unable to launch the agent for <host>
java.io.EOFException: unexpected stream termination
	at hudson.remoting.ChannelBuilder.negotiate(ChannelBuilder.java:365)
	at hudson.remoting.ChannelBuilder.build(ChannelBuilder.java:310)
	at hudson.slaves.SlaveComputer.setChannel(SlaveComputer.java:388)
	at hudson.slaves.CommandLauncher.launch(CommandLauncher.java:131)
	at hudson.slaves.SlaveComputer$1.call(SlaveComputer.java:261)
	at jenkins.util.ContextResettingExecutorService$2.call(ContextResettingExecutorService.java:46)
	at java.util.concurrent.FutureTask.run(FutureTask.java:266)
	at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
	at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
	at java.lang.Thread.run(Thread.java:745)
ERROR: Process terminated with exit code 255

That first line is a script on the master that does the SSH.    What I'm not sure about is exactly what is complaining about Host key verification.  Given I can run that script by hand and it starts the jar file I'm a bit confused about what's going on here. 

Has anybody gotten this to work?

[Donald Morton]

Sounds like the ssh command is failing. Maybe the password or private key is wrong? 

[Peter Berghold]

wish that were the case.  Nope:  running the same command from the command line yields the results I'm after.  Since the script runs as tomcat8 and tomcat8 is trusted between the hosts I'm at a complete loss as to why this is happening.

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[Dirk Heinrichs]

Am 14.11.2016 um 17:28 schrieb Peter Berghold:

[11/14/16 16:22:37] Launching agent
$ /usr/share/tomcat8/startSlave0
Host key verification failed.

There's a problem with the host key of the slave. This usually means that the SSH server (your Jenkins slave) offers a different host key than the one the SSH client (your Jenkins master) has in it's known_hosts file already. Check the ~/.ssh/known_hosts file of the user your Jenkins master runs as. If there's a key already present for the slave host, delete it. Then establish a connection to the slave via SSH from the command line (still as that very same user) and accept the new host key of the slave.

HTH...

    Dirk

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[Fritz Elfert]

On 15.11.2016 15:14, Peter Berghold wrote:
> wish that were the case. Nope: running the same command from the
> command line yields the results I'm after. Since the script runs as
> tomcat8 and tomcat8 is trusted between the hosts I'm at a complete loss
> as to why this is happening.

Really?
When manuall trying ssh to a remote slave, you *must* do that *as the
jenkins user* not with your user-account. That's because ssh stores the
remote host keys in $HOME/.ssh/known_hosts and $HOME of jenkins points
most likely somewhere else than with *your* user account. Therefore do
the following on your jenkins master:

1. sudo -i
2. su - jenkins
(or whatever your jenkins user is named on the master)
3. ssh rhelhost
(or ssh otheruser@hrelhost if named different than your master
jenkins user)

If *that* works *without* being asked any hostkey-questions, then
jenkins should be able to login too.

If *that* works *whithout* questions but jenkins still complains about
the host key, then the only explanation would be that $HOME inside the
running jenkins points somewhere else.

And BTW:

> I have Jenkins running merrily on an Ubuntu box and want to set
> up a slave on an RHEL box.

^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
If you merely want a slave host you neither need tomcat or any special
scripts for starting slave.jar, Just java on the rhel host.
If jenkins can login via ssh, it does everything automatically (copying
slave jar to the rhel-machine and starting it etc).

Cheers
-Fritz

[Fritz Elfert]

On 15.11.2016 17:26, Fritz Elfert wrote:
> most likely somewhere else than with *your* user account. Therefore do
> the following on your jenkins master:
>
> 1. sudo -i
> 2. su - jenkins
> (or whatever your jenkins user is named on the master)
> 3. ssh rhelhost
> (or ssh otheruser@hrelhost if named different than your master
> jenkins user)
>

Forgot to tell: If you don't know the jenkins user on your master, you
can lookup in the GUI: Select "Manage Jenkins->System Information"

Look for the system property named "user.name". Also the homedir is
shown there as "user.home".

Cheers