Quick start guide

This page is mainly aimed at first time users and will cover the very basics of how to get started. It will cover the following topics:

The grid certificate

A grid certificate is a way for the cluster to verify your identity. LSC members should use their LSC-provided proxy (the same used to log into LDG clusters). If you are an LSC member and have used LSC clusters, stop reading here and go to the section "Log into Holodeck".

Non LSC members need to obtain a certificate has to be approved by the IT-department of the Max-Planck-Institute Hannover. Therefore, after you have filled out the online form, you will need to pay a visit to Konrad Mors (room: 005) or Oliver Behnke (room: 037). Bring your passport!
Make sure you use your @aei.mpg.de E-Mail address when filling out the online form.

Another tip: Update your browser before applying for the certificate, as you will not be able to for the time your certificate has not been approved.

For the actual process of applying it is best to follow this tutorial.

In case you encounter any problems during this process or have any questions please contact one of the following server admins: Dr. Carsten Aulbert, Dr. Henning Fehrmann, Alexander Post.

Since the application process for the grid certificate takes a bit of time now might be a good time to install the gsissh client.

To export your certificate refer to this page.

Once the certificate is installed in the correct place run the following command.

Copy the output of the command, send it to one of the server admins Dr. Carsten Aulbert, Dr. Henning Fehrmann, Alexander Post and ask them to create your account on the cluster. Once this is done and if you have a gsissh client installed you should be able to log into the cluster.

Install globus

To install globus (i.e. the gsissh client you will need to log into Holodeck) please follow this tutorial.

Log into Holodeck

Once you have gotten your grid certificate and installed a gsissh client as described above you should be able to log into atlas. To do this you will first of all need to start a grid proxy which can be achieved by typing in the command

LSC members should instead use (with albert.einstein replaced by your MyLIGO username):

ligo-proxy-init albert.einstein

If the command was successful it will prompt you with a time during which the proxy is valid. Once this time has passed the proxy will need to be re initiated by the command above.

After the proxy is activated type
gsissh holodeck1.aei.uni-hannover.de

to connect to Holodeck. If the connection was successful the terminal should now show

You are now connected to one of the two head nodes of this cluster.

(Note: You can also set shortcuts so that you don't have to type the lengthy string all the time. See Setting SSH-config (more flexible solution) or Setting aliases (solution interesting also for other use-cases).)

Generate ssh-key

To run jobs on the work nodes you need to have an ssh-key stored in a .ssh folder of your holohome directory.

A ssh-key is a way to check credentials so that no unauthorized user has access. It consists of a private part, that should only be known to the user who generated it, and a public part, that can be handed out to anyone. This key pair can than be used to encrypt data. If data is encrypted using your private key anyone with access to your public key can decrypt it and if anything is encrypted using your public key only people with access to your private key can decrypt it.

Holodeck uses this system to check if a user is authorized to log onto the work nodes. Therefore you need to generate a ssh-key that is not protected by a password. To do so please follow the next few steps. Once you are done your account is setup and you can freely start exploring the cluster and its capabilities.

This guide assumes that you have freshly logged onto holodeck1 using

gsissh holodeck1.aei.uni-hannover.de

After you have logged on type

mkdir .ssh

This creates a directory called .ssh. If that directory already existed in the first place the command will throw an error message stating just that. That is also perfectly fine and you can continue on.

After you have created the directory, you need to change to it using

cd .ssh

The next step is to generate the ssh-key. For this run the following command and press ‘Enter’ three times when asked for input (press 'Enter' until a "picture" appears on the terminal). Not entering anything just tells the program to generate the key in the current directory and without password protection. (Using password protection may lead to difficulties when trying to schedule jobs with slurm)


Next we need to copy the public key to a file named 'authorized_keys'. To do this type

cp id_rsa.pub authorized_keys

Now you are done and should be able to log onto the work nodes using (for instance)

ssh nr01

For a more in depth summary of the nodes see the wiki-page on the available nodes.

Log out

To log out of Holodeck simply press
Ctrl D

You will return to the location you logged in from. (i.e. if you logged into one of the work nodes from one of the head nodes you will return to the head node)

See also

Useful commands · Setup a virtual environment for Python · Simple code example · slurm

-- MarlinSchFer - 12 Apr 2019
Topic revision: r10 - 25 Sep 2019, FrankOhme
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