01_logging_in.md

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theme: csc-eurocc-2019
lang: en

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Connecting to CSC Supercomputers {.title}

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/](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

  • More in-depth documentation in Docs CSC and Docs 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 [email protected] 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 [email protected] or ssh -i /path/to/ssh/keyfile [email protected]

• 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 [email protected]:/scratch/project_xxxx

  • e.g. rsync -r foldername [email protected]:/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 [email protected]

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"