This node is offline because Jenkins failed to launch the slave agent on it - jenkins

Question

I'm not sure of what the proper steps are for configuring the Jenkins master to build/deploy these jobs to a new slave, and how to set up the new slave, but it is giving an error. For instance, do I need to install anything on the new slave, or do any kind of setup/config? & I'm configuring on Ubuntu OS.
just before slave node1 gets launched ...
executing pre-launch scripts ...
[06/25/15 13:06:55] [SSH] Opening SSH connection to 192.168.4.153:22.
ERROR: Server rejected the 1 private key(s) for jenkins (credentialId:fd3affc2-25a4-4b24-9e21-275badb8b6d9/method:publickey)
ERROR: Failed to authenticate as jenkins with credential=fd3affc2-25a4-4b24-9e21-275badb8b6d9
java.io.IOException: Publickey authentication failed.
at com.trilead.ssh2.auth.AuthenticationManager.authenticatePublicKey(AuthenticationManager.java:315)
at com.trilead.ssh2.Connection.authenticateWithPublicKey(Connection.java:467)
at com.cloudbees.jenkins.plugins.sshcredentials.impl.TrileadSSHPublicKeyAuthenticator.doAuthenticate(TrileadSSHPublicKeyAuthenticator.java:109)
at com.cloudbees.jenkins.plugins.sshcredentials.SSHAuthenticator.authenticate(SSHAuthenticator.java:408)
at com.cloudbees.jenkins.plugins.sshcredentials.SSHAuthenticator.authenticate(SSHAuthenticator.java:428)
at hudson.plugins.sshslaves.SSHLauncher.openConnection(SSHLauncher.java:1173)
at hudson.plugins.sshslaves.SSHLauncher$2.call(SSHLauncher.java:701)
at hudson.plugins.sshslaves.SSHLauncher$2.call(SSHLauncher.java:696)
at java.util.concurrent.FutureTask.run(FutureTask.java:262)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1145)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615)
at java.lang.Thread.run(Thread.java:745)
Caused by: java.io.IOException: Decrypted PEM has wrong padding, did you specify the correct password?
at com.trilead.ssh2.crypto.PEMDecoder.removePadding(PEMDecoder.java:110)
at com.trilead.ssh2.crypto.PEMDecoder.decryptPEM(PEMDecoder.java:287)
at com.trilead.ssh2.crypto.PEMDecoder.decode(PEMDecoder.java:320)
at com.trilead.ssh2.auth.AuthenticationManager.authenticatePublicKey(AuthenticationManager.java:224)
... 11 more
[06/25/15 13:06:55] [SSH] Authentication failed.
hudson.AbortException: Authentication failed.
at hudson.plugins.sshslaves.SSHLauncher.openConnection(SSHLauncher.java:1178)
at hudson.plugins.sshslaves.SSHLauncher$2.call(SSHLauncher.java:701)
at hudson.plugins.sshslaves.SSHLauncher$2.call(SSHLauncher.java:696)
at java.util.concurrent.FutureTask.run(FutureTask.java:262)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1145)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615)
at java.lang.Thread.run(Thread.java:745)
[06/25/15 13:06:55] Launch failed - cleaning up connection
[06/25/15 13:06:55] [SSH] Connection closed.

Answer 1

This article explains how to connect a slave to the master using the master public ssh key:
https://www.caktusgroup.com/blog/2012/01/10/configuring-jenkins-slave/
To resume:
Generate a public SSH key on the master: ssh-keygen -t rsa (with no paraphrase)
Copy the public master key from .ssh/id_rsa.pub
On the slave, paste the public key in /home/jenkins/.ssh/authorized_keys (if /home/jenkins is your home folder)
Please confirm it solves your issue.

Answer 2

The real issue in question is Caused by: java.io.IOException: Decrypted PEM has wrong padding, did you specify the correct password? so there maybe mistake in private key text or wrong passphrase.
In my case I've got an error PEM problem: it is of unknown type with key which looks like valid:
-----BEGIN RSA PRIVATE KEY-----
...
...
-----END RSA PRIVATE KEY----
but it's not valid because I've lost last "-" character when copy/paste private key from terminal, so the right form should be:
-----BEGIN RSA PRIVATE KEY-----
...
...
-----END RSA PRIVATE KEY-----

Answer 3

The .ssh directory on the agent must have proper access permissions so that group and others do not have write permissions. The following command should make it work:
chmod 700 ~/.ssh