Connecting to the cluster

If you have not already applied for and been granted access to the cluster, then please see the Applying for access 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 UCPH VPN. For information about connecting to the VPN, see the support pages on KUnet in Danish and English. See also the Connecting on Linux section for an alternative means of connecting to the VPN.

Connecting on Windows

Windows users will need to install an 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 set up MobaXterm. Please refer to the Connecting on Linux section if using WSL.

Configuring MobaXterm

1. Install and open MobaXterm.

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

   

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

   

4. Under Basic SSH settings

   1. Write esrumhead01fl.unicph.domain under Remote Host

   2. Click the checkbox next to Specify username and enter your UCPH 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.

   

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.

   

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:

   

   Warning

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

7. You should now be able to log in to the server:

   

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

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 Sessions button on the main menu.

Accessing network drives via MobaXterm

In order to access your UCPH network drives (H:, N:, and S:) via Esrum, you must disable logins using Kerberos (GSSAPI). To do so, open the Configuration dialog as shown:

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

Connecting on OSX

While Mac/OSX users can connect as described in the Connecting on Linux section below, there are also graphical interfaces available, including for example Tabby.

Connecting on Linux

The official instructions for connecting to the VPN under Linux (in Danish and English) are written under the assumption that you are using KDE5. If that is not the case, or if you prefer a command-line solution, then you can also connect using openconnect, replacing abc123 with your UCPH username:

$ sudo openconnect -u abc123 vpn.ku.dk

Depending on how you have configured multifactor authentication for UCPH, you will have to authenticate the login using one of the following methods:

• If using NetIQ, open the app on your phone and approve the login.

• If asked, enter the time based one-time password (TOTP) generated by the app you have enrolled

Note

It may be possible to authenticate using additional methods, such as Yubikeys, but we currently cannot offer a guide to using those with openconnect.

You will likely have to install openconnect first, in which case please refer to the documentation for the Linux distro you are using. OSX users can install openconnect using Homebrew.

Once connected to the VPN, you can connect to the cluster using ssh and the following terminal command, again replacing abc123 with your UCPH username:

$ ssh abc123@esrumhead01fl.unicph.domain

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

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

This allows you to 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.

Troubleshooting

If you have not already been granted access to the server, then please see the Applying for access page before continuing!

Timeout while connecting to the cluster

You may experience timeout errors when you attempt to connect to Esrum:

On Linux:

On Windows, using MobaXterm:

Firstly verify that you are correctly connected to the UCPH VPN. This is required to connect to Esrum. See the Connecting to the cluster page for more information.

If you are still unable to connect to Esrum after verifying that you are correctly connected to the UCPH network, then please try to visit either our Project Manager or our Cohort Catalog.

If you are able to visit either of the Project Manager or Cohort Catalog pages, then you most likely do not have proper permissions to connect to Esrum. Please contact us and we will provide further guidance.

If you are unable to connect to the VPN or to either of the above pages while connected to the VPN, then there may be other problems with your account. We recommend that you either contact us for assistance or, if you prefer, that you submit a ticket to the UCPH-IT Serviceportal, using the Research Applications Counseling and Support / Forskningsapplikationer Rådgivning og support ticket category.

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 the Configuring MobaXterm section.

UCPH 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. Similarly, if using Linux or OSX, then you cannot be authenticating using a Kerberos ticket.