View source for Introduction to Linux in HPC/SSH Connections

[[Category:Tutorials|SSH Connections]]<nowiki />
{{DISPLAYTITLE:SSH Connections}}<nowiki />
{{Syllabus Introduction to Linux}}<nowiki />
__TOC__

This tutorial introduces SSH (Secure Shell) as a tool to connect to other Linux machines over a network.
It is the most common way to connect to and interact with a cluster. A SSH server is expected to be running on the remote computer, while clients for Linux, Mac OS and Windows are available to establish the connection.
This tutorials will teach you how to establish a connection and create a key for public key authentication, which is considered to be the most secure option.

=== Video === <!--T:5-->

<youtube width="600" height="340" right>j0mPVsgMOQk</youtube>

([[Media:HPC.NRW_Introduction_to_Linux_in_HPC_12_SSH_Connections.pdf | Slides as pdf]])

=== Quiz === <!--T:5-->  

{{hidden begin 
|title = What is the correct syntax to open a ssh connection?
}}
<quiz display=simple>
{
|type="()"}
+  <code>ssh [options] <username>@<hostname></code>  
||
-  <code>ssh <username>:<hostname> [options]</code>
||
-  <code>ssh [options] <username> <hostname></code>
||
</quiz>
{{hidden end}}


{{hidden begin 
|title = Where is your ssh config stored on Linux?
}}
<quiz display=simple>
{
|type="()"}
-  <code>~/sshconfig</code>  
||
-  <code>~/.config/ssh</code>
||
+  <code>~/.ssh</code>
|| Explanation: This folder contains the public and private keys for public key authentification. In <code>~/.ssh/config</code> you can define shortcuts for common ssh connections and set client configuration options.
</quiz>
{{hidden end}}


{{hidden begin 
|title = What tools help you with creating and installing a ssh key-pair? (on Linux)
}}
<quiz display=simple>
{
|type="()"}
+  <code>ssh-keygen</code> to create the key files and <code>ssh-copy-id</code> to copy it to the remote machine
||
- <code>ssh --keygen</code> to create the key files and <code>ssh --copy-id</code> to copy it to the remote machine
||
</quiz>
{{hidden end}}

{{hidden begin 
|title = Does it cause a security problem to share an SSH public key with your friends?
}}
<quiz display=simple>
{
|type="()"}
-  Yes
|| 
+  No
|| Explanation: SSH public key authentication uses the asymmetric encryption. Therefore, it's completely safe to share your SSH public key. But you must keep your SSH private key as top secret.
</quiz>
{{hidden end}}


{{hidden begin 
|title = Which authentication for SSH login is more secure?
}}
<quiz display=simple>
{
|type="()"}
-  password authentication
|| 
+  public key authentication
|| Explanation: The password based authentication may be exposed to the brute-force password attack. Please use the SSH public key authentication.
</quiz>
{{hidden end}}


{{hidden begin 
|title = When generating the SSH public/private key pair, is it secure to use empty passphrase?
}}
<quiz display=simple>
{
|type="()"}
-  Yes
|| 
+  No
|| Explanation: Please never ever use an empty passphrase for the SSH key pair. Use strong passphrase to generate the SSH key pair.
</quiz>
{{hidden end}}


{{Warning|mode=info|text='''Verify the fingerprint of remote host, before the first login.'''<br>'''User the SSH public key authentication for login.'''<br>'''Never use an empty passphrase for the SSH keys.'''<br>'''Use strong passphrase to generate the SSH keys.'''<br>'''Keep your private SSH key as top secret.'''<br>'''Create, configure and use different SSH keys for different remote hosts.'''<br>  '''If no X11 application is required, disable X11 forwarding. Otherwise, only enable the untrusted X11 forwarding.'''
}}

{{Tutorial Navigation
| previous = [[Introduction_to_Linux_in_HPC/System_configuration_files  | System configuration files ]]
| main = [[Introduction_to_Linux_in_HPC | Overview ]]
| next = [[Introduction_to_Linux_in_HPC/SSH_Graphics_File_Transfer | SSH: Graphics and File Transfer]]
}}