SSH, remote login with with secure shell¶

Introduction¶

This manual will help you set up a connection to another computer using ssh. This is especially useful for connecting from your desktop or laptop to a HPC server. The resulting connection will give you a command line interface (terminal) in which you can start your application and manage your data. In most cases the server will run Linux so you will need to know how to use the Linux command line.

You can find the available HPC servers via this link.

Besides logging in to remote computer you can also use the ssh connection for filetransfer. This method is named SFTP. More information about this can be found in data_transfer.

This document will explain how to install a SSH client and how to setup an SSH connection.

Install¶

Linux/macOS¶

All Linux-distributions and macOS provide an SSH-client. If it is not available you can install it via the package-manager:

yum (RedHat, Fedora, CentOS)

$ sudo yum install openssh-client

apt (Debian, Ubuntu)

$ sudo apt install openssh-client

brew (macOS)

$ brew install openssh

After installation you can connect to the server with:

$ ssh <netid>@hpc29.tudelft.net

Windows¶

Currently MobaXterm is the preferred SSH client for Windows. On older Windows installation PuTTY might be installed, which is also a great SSH client but with less possibilities.

MobaXterm¶

The MobaXterm package allows you to connect to servers and access all files in the current directory of your SSH connection. The Portable Home Edition version can be installed free of charge without administrator rights. If you do have administrator rights consider installing the Installer Home Edition:

https://mobaxterm.mobatek.net/download-home-edition.html

If you would like to access the HPC cluster follow these instructions to setup a connection to login1.hpc.tudelft.nl via linux-bastion.tudelft.nl (or student-linux.tudelft.nl if you are a student):

goto Settings→Configuration menu
select SSH tab, deselect GSSAPI Kerberos and click OK:
goto Sessions→New session menu
select SSH tab and fill in the following fields:
1. Remote host: login1.hpc.tudelft.nl
2. enable Specify username and enter your NetID
select Network settings tab in the middle of the window, click SSH gateway (jump host), fill in the following fields and click OK:
1. Gateway host: linux-bastion.tudelft.nl (or student-linux.tudelft.nl if you are a student)
2. Username: your NetID
click OK in the Session settings window
enter your NetID password for the connection to the linux-bastion.tudelft.nl (student-linux.tudelft.nl):
on the left side you will now see your new session named login1.hpc.tudelft.nl. Double click this session
the first time you start this session you might be required to fill in your NetID password again. After that you can decide to store your password(s) in MobaXterm by clicking yes
fill in the fields for your MobaXterm Master Password and click OK
now the connection to the head node is started and the first time you are required to fill in your NetID password in the black screen after the prompt. NOTE: you will not see the cursor moving while typing; this is intentionally!
again you are requested to save your password. This time this is the password for login1.hpc.tudelft.nl.
the SSH connection to the head node is now up and you can start working on the cluster

After this initial configuration you can reconnect to the head node by clicking on the session (on the left hand side) and you will not have to enter your password again (not for the bastion and not for the head node).

PuTTY¶

You can download PuTTY here: https://www.putty.org/. After installation you can connect to the server as follows:

Start the PuTTY program
Fill in the name of the HPC server you would like to connect to:
Disable GSSAPI under Connection→SSH→Auth→GSSAPI:

GSSAPI allows you to login via SSH using your Windows credentials. Although this is convenient, some functionality in Linux fails with this service.
Click Open to start the connection
If this is the first time you connect to this server, you will see the following window:
Click Yes to accept this key. Actually it’s a good idea to first read the message in this window!
A terminal window will open asking for your netid (grayed-out blocks) and password. Note: during the typing of your password you will not see any output on the screen:
You now have an SSH-connection to the HPC-server and you will get a green cursor after the prompt $ where you can start typing

WSL with Ubuntu¶

The WSL in Windows 10 allow you to install Ubuntu (a Linux OS). After installation a terminal with a shell can be started and most of the Linux programs are available. As such also ssh can be started. If needed the graphic output of the SSH-server can also be shown when in Windows an X-client is installed and activated (e.g. Xming).

Usage¶

Over the years the SSH protocol has evolved and now enables a multitude of ways to connect from one computer to the next. In this chapter several of these techniques are described each with their own merit and usefulness. An overview of these techniques which will be discussed later:

Plain SSH

Plain SSH

Tunnel

Tunnel

Multiplex

Multiplex

Proxyjump

Proxyjump

SSH requires authentication to ensure the integrity of user trying to access the server and to setup a encrypted connection. In this document we will discuss three different authentication mechanisms:

Password authentication	Key-pair authentication	Kerberos authentication

Which combination of technique and authentication is used depends on the configuration of the client and the server. In the table below you will find some combinations found at the TU Delft:

client→ server↓	Windows TU installed	Windows	macOS/Linux
linux-bastion	multiplex, password	multiplex, password	multiplex, password
HPC head nodes	proxyjump & multiplex, password	proxyjump & multiplex, password	proxyjump & multiplex, password
awi servers	proxyjump & multiplex, key	proxyjump & multiplex, key	proxyjump & multiplex, key

under construction

Good luck!