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Type: Bug
Resolution: Fixed
Priority: Critical
Component/s: ssh-slaves-plugin
Labels:
- regression
Environment:
Versions:

Jenkins: 2.51
SSH Agent Plugin: 1.14
SSH Credentials plugin: 1.13
SSH Slaves Plugin : 1.15

Ubuntu 14.04, 16.04

Similar Issues:

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SSH agent isn't launched after the latest update, complaining about missing records in the known hosts file.

Nevertheless, the records do exist. I've tried to connect manually with ssh, everything was fine, ssh reports that it has found the host in known_hosts.

Probable reason is the hashed host name in known_hosts.

Here is the log from the Jenkins slave launch page:

[03/21/17 11:40:34] [SSH] Opening SSH connection to xxx.xxx.xxx.xxx:22
[03/21/17 11:40:34] [SSH] WARNING: No entry currently exists in the Known Hosts file for this host.      Connections will be denied until this new host and its associated key is added to the Known Hosts file.
     Key exchange was not finished, connection is closed.
     java.io.IOException: There was a problem while connecting to xxx.xxx.xxx.xxx:22
	at com.trilead.ssh2.Connection.connect(Connection.java:818)
	at com.trilead.ssh2.Connection.connect(Connection.java:687)
	at com.trilead.ssh2.Connection.connect(Connection.java:601)
	at hudson.plugins.sshslaves.SSHLauncher.openConnection(SSHLauncher.java:1265)
	at hudson.plugins.sshslaves.SSHLauncher$2.call(SSHLauncher.java:790)
	at hudson.plugins.sshslaves.SSHLauncher$2.call(SSHLauncher.java:785)
	at java.util.concurrent.FutureTask.run(FutureTask.java:262)
	at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1145)
	at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615)
	at java.lang.Thread.run(Thread.java:745)
     Caused by: java.io.IOException: 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)
	... 9 more
     Caused by: java.io.IOException: The server hostkey was not accepted by the verifier callback
	at com.trilead.ssh2.transport.KexManager.handleMessage(KexManager.java:591)
	at com.trilead.ssh2.transport.TransportManager.receiveLoop(TransportManager.java:777)
	at com.trilead.ssh2.transport.TransportManager$1.run(TransportManager.java:489)
	... 1 more
     [03/21/17 11:40:34] Launch failed - cleaning up connection
     [03/21/17 11:40:34] [SSH] Connection closed.

And this is the debug output from ssh, showing that it has found a record in the second line of known_hosts.

  $ sudo -u jenkins -g jenkins ssh -v jenkins@xxx.xxx.xxx.xxx
    OpenSSH_6.6.1, OpenSSL 1.0.1f 6 Jan 2014
    debug1: Reading configuration data /etc/ssh/ssh_config
    debug1: /etc/ssh/ssh_config line 19: Applying options for *
    debug1: Connecting to xxx.xxx.xxx.xxx [xxx.xxx.xxx.xxx] port 22.
    debug1: Connection established.
    debug1: identity file /var/lib/jenkins/.ssh/id_rsa type 1
...
    debug1: sending SSH2_MSG_KEX_ECDH_INIT
    debug1: expecting SSH2_MSG_KEX_ECDH_REPLY
    debug1: Server host key: ECDSA xx:xx:xx:xx:xx:xx:xx:xx:xx:xx:xx:xx:xx:xx:xx:xx:xx
    debug1: Host 'xxx.xxx.xxx.xxx.xxx' is known and matches the ECDSA host key.
    debug1: Found key in /var/lib/jenkins/.ssh/known_hosts:2
    debug1: ssh_ecdsa_verify: signature correct
...
    Welcome to Ubuntu 16.04.2 LTS (GNU/Linux 4.4.0-67-generic x86_64)

Additional logs from Jenkins system log:

Mar 21, 2017 12:06:08 PM FINER com.trilead.ssh2.transport.KexManager
    kex_algo=diffie-hellman-group14-sha1
Mar 21, 2017 12:06:08 PM FINER com.trilead.ssh2.transport.KexManager
    server_host_key_algo=ssh-rsa
    Mar 21, 2017 12:06:08 PM FINER com.trilead.ssh2.transport.KexManager
    enc_algo_client_to_server=aes256-ctr
    Mar 21, 2017 12:06:08 PM FINER com.trilead.ssh2.transport.KexManager
    enc_algo_server_to_client=aes256-ctr
    Mar 21, 2017 12:06:08 PM FINER com.trilead.ssh2.transport.KexManager
    mac_algo_client_to_server=hmac-sha1
    Mar 21, 2017 12:06:08 PM FINER com.trilead.ssh2.transport.KexManager
    mac_algo_server_to_client=hmac-sha1
    Mar 21, 2017 12:06:08 PM FINER com.trilead.ssh2.transport.KexManager
    comp_algo_client_to_server=none
    Mar 21, 2017 12:06:08 PM FINER com.trilead.ssh2.transport.KexManager
    comp_algo_server_to_client=none
    Mar 21, 2017 12:06:08 PM FINE com.trilead.ssh2.transport.TransportManager
    Receive thread: error in receiveLoop
    java.io.IOException: The server hostkey was not accepted by the verifier callback
            at com.trilead.ssh2.transport.KexManager.handleMessage(KexManager.java:591)
            at com.trilead.ssh2.transport.TransportManager.receiveLoop(TransportManager.java:777)
            at com.trilead.ssh2.transport.TransportManager$1.run(TransportManager.java:489)
            at java.lang.Thread.run(Thread.java:745)

    Mar 21, 2017 12:06:08 PM FINER com.trilead.ssh2.transport.TransportManager
    Receive thread: back from receiveLoop
    Mar 21, 2017 12:06:10 PM FINER com.trilead.ssh2.transport.KexManager
    kex_algo=diffie-hellman-group14-sha1
    Mar 21, 2017 12:06:10 PM FINER com.trilead.ssh2.transport.KexManager
    server_host_key_algo=ssh-rsa
    Mar 21, 2017 12:06:10 PM FINER com.trilead.ssh2.transport.KexManager
    enc_algo_client_to_server=aes256-ctr
    Mar 21, 2017 12:06:10 PM FINER com.trilead.ssh2.transport.KexManager
    enc_algo_server_to_client=aes256-ctr
    Mar 21, 2017 12:06:10 PM FINER com.trilead.ssh2.transport.KexManager
    mac_algo_client_to_server=hmac-sha1
    Mar 21, 2017 12:06:10 PM FINER com.trilead.ssh2.transport.KexManager
    mac_algo_server_to_client=hmac-sha1
    Mar 21, 2017 12:06:10 PM FINER com.trilead.ssh2.transport.KexManager
    comp_algo_client_to_server=none
    Mar 21, 2017 12:06:10 PM FINER com.trilead.ssh2.transport.KexManager
    comp_algo_server_to_client=none
    Mar 21, 2017 12:06:10 PM FINE com.trilead.ssh2.transport.TransportManager
    Receive thread: error in receiveLoop
    java.io.IOException: The server hostkey was not accepted by the verifier callback
            at com.trilead.ssh2.transport.KexManager.handleMessage(KexManager.java:591)
            at com.trilead.ssh2.transport.TransportManager.receiveLoop(TransportManager.java:777)
            at com.trilead.ssh2.transport.TransportManager$1.run(TransportManager.java:489)
            at java.lang.Thread.run(Thread.java:745)

    Mar 21, 2017 12:06:10 PM FINER com.trilead.ssh2.transport.TransportManager
    Receive thread: back from receiveLoop

File /var/lib/jenkins/.ssh/known_hosts contains strings, looking like being base64-encoded, delimited by '|'. Here is the sample.

|1|DAg  ...   o... 1ll9wI=| ...  ....  tIrM= ecdsa-sha2-nistp256 xxxxxx..... bmlzdHAyNTYAAAAIbm................. .................xxxxxxxxxxxoKEHF3Vr0q685jI2+6vWjvAAG4lz5Ckujy9k=

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