SSH client on Windows

Significant changes to authentication coming in April 2025

Starting April 14 2025, SSH login to Puhti and Mahti will only work using SSH keys added in MyCSC. Password authentication and public keys stored in users' personal ~/.ssh/authorized_keys file on the supercomputer will no longer work. This authentication method is already in use on LUMI.

Read the detailed instructions on setting up and using SSH keys.

There are various programs that can be used for creating a remote SSH connection on a Windows system. This page provides instructions for three popular alternatives: PowerShell, PuTTY and MobaXterm.

PowerShell

Basic usage (PowerShell)

You can use the Windows PowerShell command-line shell to connect to a CSC supercomputer using the Win32 OpenSSH client. To install OpenSSH on a Windows device, follow these installation instructions. After installing OpenSSH, you can connect to a CSC supercomputer by opening PowerShell and running:

# Replace <username> with the name of your CSC user account and
# <host> with "puhti" or "mahti"

ssh <username>@<host>.csc.fi

Graphical connection (PowerShell)

If you want to create a connection with graphical support, you can use, for example, the Xming X server. To enable displaying graphics remotely, run:

$env:DISPLAY="localhost:0.0"

Then, use the -X (X11 forwarding) or -Y (trusted X11 forwarding) option when creating the connection:

ssh -X <username>@<host>.csc.fi

Generating SSH keys (PowerShell)

You can generate SSH keys using PowerShell by running:

ssh-keygen -o -a 100 -t ed25519

Using SSH keys

See the page on setting up SSH keys for general information about using SSH keys for authentication.

Copying public key to supercomputer (PowerShell)

Starting April 14 2025, the only way to copy a public key to a supercomputer is through the MyCSC customer portal. Read the instructions here.

Authentication agent (PowerShell)

To avoid having to type your passphrase every time you connect, you can configure the Windows SSH agent to store your keys in memory for the duration of your local login session.

Corrupted MAC on input

When connecting using the OpenSSH client software on Windows, you might encounter an error stating "Corrupted MAC on input". This is a known issue, and can be avoided by explicitly choosing a different MAC algorithm. For details, please see our FAQ page on the topic.

PuTTY

Basic usage (PuTTY)

The PuTTY SSH client is an alternative to using OpenSSH. When you launch PuTTY, you are asked to configure your SSH session. Do so according to the table below and click Open.

Option	Value
Host Name	`puhti.csc.fi` or `mahti.csc.fi`
Port	`22`
Connection type	`SSH`

Graphical connection (PuTTY)

If you want to create a connection with graphical support, you can use, for example, the Xming X server. To enable displaying graphics remotely, select Enable X11 forwarding in the PuTTY program settings (Connection --> SSH --> X11).

Generating SSH keys (PuTTY)

To generate SSH keys for connecting with PuTTY, use the PuTTYgen key generator. The PuTTY documentation provides instructions for using PuTTYgen.

Using SSH keys

See the page on setting up SSH keys for general information about using SSH keys for authentication.

Copying public key to supercomputer (PuTTY)

Starting April 14 2025, the only way to copy a public key to a supercomputer is through the MyCSC customer portal. Read the instructions here.

Connecting with SSH keys (PuTTY)

When creating a remote connection using PuTTY, select the private key file under Connection --> SSH --> Auth. If you want the private key to be used each time you connect, save your session to store your choice.

Authentication agent (PuTTY)

To avoid having to type your passphrase every time you connect, you can use the Pageant authentication agent to store your private keys in memory.

MobaXterm

Basic usage (MobaXterm)

MobaXterm is an SSH client with an embedded X server, which means that it can be used to display graphics. To connect using MobaXterm, open the terminal and run:

# Replace <username> with the name of your CSC user account and
# <host> with "puhti" or "mahti"

ssh <username>@<host>.csc.fi

Graphical connection (MobaXterm)

To enable displaying graphics over SSH, use the -X (X11 forwarding) or -Y (trusted X11 forwarding) option when creating the connection:

ssh -X <username>@<host>.csc.fi

Generating SSH keys (MobaXterm)

You can generate SSH keys using MobaXterm by running:

ssh-keygen -o -a 100 -t ed25519

If you want your generated keys to persist through MobaXterm restarts, set a persistent home directory for MobaXterm in the program settings (Settings --> Configuration --> General).

Using SSH keys

See the page on setting up SSH keys for general information about using SSH keys for authentication.

Copying public key to supercomputer (MobaXterm)

Starting April 14 2025, the only way to copy a public key to a supercomputer is through the MyCSC customer portal. Read the instructions here.

Authentication agent (MobaXterm)

To avoid having to type your passphrase every time you connect, enable the MobAgent authentication agent in the program settings (Settings --> Configuration --> SSH).