Connecting to CSC Supercomputers

This topic is about how to login to the CSC supercomputers.

All materials (c) 2020-2025 by CSC – IT Center for Science Ltd. This work is licensed under a Creative Commons Attribution-ShareAlike 4.0 Unported License, http://creativecommons.org/licenses/by-sa/4.0/

Login via the web interfaces

  • A simple way to login to the Puhti supercomputer is via puhti.csc.fi
  • Login requires multi-factor authentication (MFA)
    • Haka is recommended if your home organization already requires MFA
    • Otherwise, activate CSC MFA in MyCSC and use your CSC credentials
  • The web interface can be used, e.g., to launch GUI applications, browse files or open a command-line shell
    • The latter is useful if your computer does not have an SSH client, but you need command-line access to the supercomputer
  • Similar web interfaces are also available for Mahti and LUMI

Login with SSH (1/2)

  • SSH is a terminal program that gives you command-line access on the CSC supercomputer
  • It is a versatile main interface to a supercomputer
    • Laptop ↔︎ Toyota, Supercomputer ↔︎ F1. F1 needs a specialist interface.
  • Logging in with SSH requires setting up SSH keys
    • A key pair is created and the public key is uploaded to MyCSC
    • Using SSH keys is easier and safer than using a password with every login
    • Read the documentation and do the tutorial
    • Consult the FAQ or contact to troubleshoot issues

Login with SSH (2/2)

  • After adding your public key to MyCSC, it takes 30-60min for it to sync to Puhti. Once done, you may log in using ssh command
    • Example: ssh cscusername@puhti.csc.fi or
      ssh -i /path/to/ssh/keyfile cscusername@puhti.csc.fi
  • Detailed instructions for logging in with SSH on macOS and Linux and on Windows
    • On Windows, we recommend MobaXterm or PuTTY clients, or simply using the web interfaces instead of SSH
  • Note! Plain SSH will not allow displaying remote graphics
    • The web interfaces are often best for this, but a graphical connection can also be enabled over SSH using X11 forwarding

Moving files between a local computer and Puhti

  • scp and rsync are powerful command-line tools to copy files
    • scp works even in Windows PowerShell (but rsync is missing)
    • e.g. scp filename cscusername@puhti.csc.fi:/scratch/project_xxxx
    • e.g. rsync -r foldername cscusername@puhti.csc.fi:/scratch/project_xxxx
    • rsync exists in MobaXterm but it removes write permissions of copied files
  • Sometimes a GUI tool for transferring files is more convenient
    • Nice tools are e.g. FileZilla and WinSCP
    • MobaXterm also has a file transfer GUI (Tip: set persistent home directory)
    • The web interfaces can also be used to easily upload/download files
  • Note! Both the command-line and graphical file transfer tools are inherently SSH-based, so using them at CSC requires SSH keys!

Moving files between Puhti and Mahti (1/2)

  • SSH keys should be set up on your local computer
  • To access Mahti from Puhti, or vice versa, you must ensure your SSH keys are forwarded to the server from where you want to connect onward
    • This is called SSH agent forwarding
    • Allows using e.g. rsync or scp to move files directly between Puhti/Mahti
  • On Linux/macOS, add option -A to your SSH command
    • Example: ssh -A cscusername@puhti.csc.fi

Moving files between Puhti and Mahti (2/2)

  • Using MobaXterm:
    • Similar to Linux/macOS if using local terminal, otherwise toggle Allow agent forwarding under “Session” -> “SSH” -> “Advanced SSH settings” -> “Expert SSH settings”
  • Using PuTTY:
    • Select “SSH” -> “Connection” -> “Auth” and toggle option Allow agent forwarding under “Other authentication-related options”