Ssh – How to resolve the “invalid ELF header” warning when trying to SSH and what does it mean

sshUbuntu

I'm getting some kind of warning when checking my connection to github. Why is it happening and how can I resolve it?

$ ssh -TI ~/.ssh/id_rsa git@github.com
dlopen /home/ubuntu/.ssh/id_rsa failed: /home/ubuntu/.ssh/id_rsa: invalid ELF header
Hi mediapop/Gnossem-Magazine! You've successfully authenticated, but GitHub does not provide shell access.

Best Answer

You mistaken options -i and -I of OpenSSH.

From man ssh:

-I pkcs11 - Specify the PKCS#11 shared library ssh should use to communicate with a PKCS#11 token providing the user's private RSA key.

-i identity_file - Selects a file from which the identity (private key) for public key authentication is read.

After -I ssh expects shared library and tries to load your id_rsa as shared library, so it expects ELF header.

In this case you can omit -i because ~/.ssh/id_rsa is default file.

Related Solutions

SSH Broken Pipe – Understanding the Broken Pipe Message in SSH Sessions

It's possible that your server closes connections that are idle for too long. You can update either your client (ServerAliveInterval) or your server (ClientAliveInterval)

 ServerAliveInterval
         Sets a timeout interval in seconds after which if no data has
         been received from the server, ssh(1) will send a message through
         the encrypted channel to request a response from the server.  The
         default is 0, indicating that these messages will not be sent to
         the server.  This option applies to protocol version 2 only.

 ClientAliveInterval
         Sets a timeout interval in seconds after which if no data has
         been received from the client, sshd(8) will send a message
         through the encrypted channel to request a response from the
         client.  The default is 0, indicating that these messages will
         not be sent to the client.  This option applies to protocol
         version 2 only.

To update your server (and restart your sshd)

echo "ClientAliveInterval 60" | sudo tee -a /etc/ssh/sshd_config

Or client-side:

echo "ServerAliveInterval 60" >> ~/.ssh/config

SSH – SSH Shell via SSH Proxy

You might want to look into ssh's ProxyCommand configuration, which allows for this to work more seamlessly, and will work for shells, SFTP, tunnels, and anything else you might want to proxy via ssh.

Let's say you have the following three hosts:

workstation.example.com - This is the machine you're physically working on
proxy.example.com - This is the machine you're routing your SSH traffic through
endpoint.example.com - This is where you want the traffic to ultimately end up

In ~/.ssh/config on workstation, add the following:

Host endpoint
    User EndpointUser # set this to the username on the destination host
    HostName endpoint.example.com
    ProxyCommand ssh username@proxy.example.com nc %h %p 2> /dev/null

On the proxy host, make sure nc (netcat) is installed.

Then, on workstation, you can ssh endpoint or sftp endpoint and you will be transparently proxied to the machine by way of your proxy host.

Best Answer

Related Solutions

SSH Broken Pipe – Understanding the Broken Pipe Message in SSH Sessions

SSH – SSH Shell via SSH Proxy

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