4.1.2. Connecting to the cluster#

If you have not already applied for and been granted access to the cluster, then please see the Accessing the cluster page before continuing.

The cluster's is accessible via SSH at esrumhead01fl.unicph.domain. This is the Esrum "head" node, which serves as the entry-point for the cluster and which gives you access to the job management system used for running software (see Running jobs using Slurm)

To connect to the cluster you will typically need to be connected to the KU VPN. For information about connecting to the VPN, see the support pages on KUNet in Danish and English.

4.1.2.1. Connecting on Windows#

Windows users will need to install a SSH client in order to be able to connect to the server. Options include MobaXterm, Putty, and Windows Subsystem for Linux (WSL), and much more. The following demonstrates how to setup MobaXterm. Please refer to the Connecting On Linux or OSX section if using WSL.

4.1.2.1.1. Configuring MobaXterm#

  1. Install and open MobaXterm.

  2. Click left-most Session button on the toolbar.

    ../../_images/mobaxterm_01.png

  3. Click on the left-most SSH button on the resulting Session settings dialog

    ../../_images/mobaxterm_02.png

  4. Under Basic SSH settings

    1. Write esrumhead01fl.unicph.domain under Remote Host

    2. Click the checkbox next to Specify username and enter your KU username (in the form abc123)

    3. Select SCP (enhanced speed) on the SSH-browser type drop-down menu. This is required for file-uploads to work.

    ../../_images/mobaxterm_03.png

  5. Click on the Bookmark settings tab and

    1. Write Esrum or a name you prefer under Session Name

    2. Optionally click the Create a desktop shortcut to this session button. This will create a shortcut on your desktop that connects to Esrum.

    ../../_images/mobaxterm_04.png

  6. Click OK and you should connect to the server. The first time you connect a new server you if you want to proceed. As this is the first time we are connecting to Esrum, simply press Accept:

    ../../_images/mobaxterm_05.png

    Warning

    If you receive this question again later, then stop and double-check that you are connected via the KU VPN, as the message could indicate that you are not actually connecting to Esrum!

  7. You should now be able to login to the server:

    ../../_images/mobaxterm_06.png

  8. For security reasons we recommend that you decline if asked if you want to save your password.

4.1.2.1.2. Reconnecting with MobaXterm#

To connect again another time, either use the desktop shortcut (if you created it), double click on Esrum in the list of sessions on the left side of MobaXterm, or select Esrum from the list that appears when clicking on the middle Sessions button on the main menu.

../../_images/mobaxterm_07.png

Note that you must disable login using Kerberos (GSSAPI) if you wish to access the KU network drives (H: and N:) via Esrum. To do so, open the Configuration dialog as shown:

../../_images/mobaxterm_08.png

Then untick the GSSAPI Kerberos checkbox as shown and click the OK button:

../../_images/mobaxterm_09.png

4.1.2.2. Connecting on Linux or OSX#

Linux and OSX users can connect to the cluster using the following terminal command, replacing abc123 with your KU username:

$ ssh abc123@esrumhead01fl.unicph.domain
../../_images/connecting_ssh.gif

It is recommended to add an entry for the cluster to your .ssh/config file, replacing abc123 with your KU username:

$ cat ~/.ssh/config
Host esrum esrumhead01fl esrumhead01fl.unicph.domain
    HostName esrumhead01fl.unicph.domain
    User abc123

This allows you connect to the server using the names esrum, esrumhead01fl, or esrumhead01fl.unicph.domain, and without having to specify your username:

$ ssh esrum
abc123@esrumhead01fl.unicph.domain's password:
     __
    /  \
   _\__/  Welcome to esrumhead01fl
  (_)     University of Copenhagen
_____O______________________________________
Supported by UNICPH IT  it.ku.dk/english


Last login: Fri Oct 13 01:35:00 1980 from 127.0.0.1
$

Note

Note that the cluster does not support authentication through a public SSH key and that you therefore have to enter your password when connecting to the server.

4.1.2.3. Troubleshooting#

If have not already been granted access to the server, then please see the Accessing the cluster page before continuing!

4.1.2.3.1. Timeout while connecting to the cluster#

You may experience timeout errors when you attempt to connect to the server:

../../_images/connecting_ssh_timeout.gif

  1. Firstly verify that you are (still) a member of the appropriate group as described in Applying for access to the cluster, as KU-IT may automatically revoke your memberships under certain conditions. No notifications are sent when that happens!

  2. Secondly verify that you are correctly connected to the KU network:

    1. You must either use a wired connection while physically at CBMR.

    2. Or you must connect via the KU VPN.

    It is not possible to connect to using WIFI at CBMR nor is it possible to from outside of CBMR without the use of the VPN. See the official VPN documentation in Danish or English for more information.

  3. If neither using a wired connection nor connecting the the KU VPN fixes the problem, you may need to create a support ticket to have KU IT permit you to connect to the server.

    1. Login to the KU IT Serviceportal.

    2. Click the Create Ticket / Opret Sag button.

    3. Tick/select the Research IT / Forsknings IT category in the category/filters list on the left side of the screen.

    4. Click the Research Applications Counseling and Support / Forskningsapplikationer Rådgivning og support button.

    5. Click the REQUEST / Bestil button.

    6. Write something like "SSH connection times out when attempting to connect to esrumhead01fl.unicph.domain" in the "Please describe" text-box and describe the steps you have taken to try to fix this problem: Tried wired connection at CBMR, tried VPN, etc.

    7. Write "esrumhead01fl.unicph.domain" in the System name text-box.

    8. Click the Review & submit / Gennemse & bestil button.

    9. Review your ticket and then click the Submit / Bestil button.

Warning

If you are not an employee at CBMR you may not have permission to open a ticket as described above. In that case simply Contact us and we will forward your issue to KU-IT.

4.1.2.3.2. File uploads using MobaXterm never start#

Please make sure that your session is configured to use the SCP (enhanced speed) browser type. See step 4 in in the Configuring MobaXterm section.

4.1.2.3.3. KU network-folders in ~/ucph are not available when using MobaXterm#

Please make sure that you have disabled use of GSSAPI Kerberos as described in the Configuring MobaXterm section.