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For an overview of the LUMI supercomputer, see the LUMI documentation.

Puhti and Mahti are CSC's supercomputers. Puhti has been available for CSC users since 2 September 2019 and Mahti has been available since 26 August 2020. LUMI is one of the pan-European pre-exascale supercomputers, located in CSC's data center in Kajaani. The CPU partition of LUMI (LUMI-C) has been available since early 2022, and the full system with the large LUMI-G partition has been available since early 2023.

Puhti contains CPU nodes with a range of memory sizes as well as a large GPU partition (Puhti AI), while Mahti contains homogeneous CPU nodes and is meant for larger jobs (minimum 128 CPU-cores). Mahti also contains a GPU partition since 2021 (Mahti AI) with Nvidia Ampere GPUs. See specifications for details on the systems and this page for an outline of differences between LUMI-C and Mahti.

CSC supercomputers use the Linux operating system and we recommend that you are familiar with basics of Linux command line usage before starting.

Accessing Puhti and Mahti

To be able to use CSC's supercomputers, you need to have a CSC user account that belongs to a computing project which has access to the respective supercomputers. CSC user accounts and projects are managed in the MyCSC portal. Further instructions are provided in the Accounts section of this user guide.


To access the LUMI supercomputer, you need to create a LUMI-specific project. For more details on getting started with LUMI, see the LUMI documentation.

Connecting to the supercomputers

Connect using an ssh client:




This will connect you to one of the login nodes. If you need to connect to a specific login node, use the command:

ssh yourcscusername@puhti-login<number 11-12,14-15>


ssh yourcscusername@mahti-login<number 11-12>

Where yourcscusername is the username you get from CSC.

For more details, see the connecting page.

Puhti can also be accessed via the Puhti web interface available at


Don't allocate more resources to your job than it can use efficiently. This needs to be verified for each new code and job type (different input) by a scaling test. The policy is that the job should be at least 1.5 times faster when you double the resources (cores). Instructions for performing a scalability test. Please also consider other important factors related to performance.

Projects and quotas

Working in CSC supercomputers is based on projects. The computing and storage resources are allocated to projects and when you start a batch job, you must always define the project that the job belongs to.

Projects are managed in the MyCSC portal, where you can add services, resources and users to your CSC projects.

In CSC supercomputers, you can check your currently active projects with the command:


This command shows information for all your CSC projects. You can select just one project to be reported with the -p option. For example:

[kkayttaj@puhti ~]$ csc-projects -p project_2012345
Project: project_2012345    Owner: Kalle Käyttäjä
Title: "Ortotopology modeling"
Start: 2015-12-17 End: 2022-03-16 Status: open
Budget:   1174188  Used   1115284 Remain:      58904
Latest resource grant: 2019-03-04

The command reports the owner of the project, title, start and end dates. In addition the command prints out the budgeting information for the project: how many billing units have been granted to your project, how many have been used and how many still remain.

The disk areas of your projects can be checked with the command:


Using Puhti and Mahti

Last update: August 16, 2023