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Institute for Advanced Simulation (IAS)

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Logging on to JUQUEEN

Dispatch

Prerequisite for using the JUQUEEN system is to successfully pass through the application process. All details can be found at the website Allocation of computing time for the central computing systems (english version).

Login Nodes

The IBM Blue Gene/Q uses so called front-end nodes or login nodes for interactive access and the submission of batch jobs.

JUQUEEN has two different login nodes (juqueen1 and juqueen2) which may be addressed as:

juqueen.fz-juelich.de

The front-end nodes have an identical environment, but multiple sessions of one user may reside on different nodes which must be taken into account when killing processes.

Access with ssh

Generating a key

Users can't login by suppling username/password credentials. Instead, password free login based on SSH key exchange is required.

The public/private ssh key pair has to be generated on the system from which you want to access JUQUEEN and stored in the $HOME directory. On Linux or UNIX-based systems, the key pair can be generated by executing

ssh-keygen -t [dsa|rsa]

Please protect the ssh key with a non-trivial pass phrase to fulfill the FZJ security policy. (For further details on ssh key generation see FAQ: How to generate ssh keys)

The generated public ssh key contained in the file id_dsa.pub or id_rsa.pub on your system must be uploaded through the JSC WEB interface when initially applying for a userid and will be appended to $HOME/.ssh/authorized_keys.

In case your ssh key got lost or needs to be updated, you can use the dispatch ssh-key upload page, to upload a new key. In either case the key will be put to the file
$HOME/.ssh/authorized_keys
on the JUQUEEN system.

Note: Please make sure that your $HOME directory is not open for write access for other groups or world, otherwise .ssh will not work.

Login

After that a typical login looks like

ssh <userid>@juqueen.fz-juelich.de

juqueen is a generic name which will either establich a connection to juqueen1 or juqueen2.

Comment: Too many accesses (ssh or scp) within a short amount of time will be interpreted as intrusion and leads to automatic disabling the origin system at the FZJ firewall.
For transferring multiple files in a single scp session the -r option can be used, which allows to transfer a whole directory.

X11 Forwarding

If a login is done via multiple machines, the X11 forwarding must be enabled in the file .ssh/config with:

PubkeyAuthentication yes
ForwardAgent yes
ForwardX11 yes

Home Data

JUQUEEN users have access to their home data in a common General Parallel File System (GPFS). For organization of the home data in respect to using multiple systems it is strongly recommended to add new subdirectories in $HOME for new machines.

Attention: Please do NOT rename or reorganize the directory structure of the existing directories because this will cause recall and backup activities for every changed file due to path or name modifications.

Login Shell

The Login Shell on each system points to system's favored shell:

JUQUEEN -> bash

Users are not allowed to change the Login Shell but they can switch to a personal shell within the login process. User's will find a template within the initial FZJ .profile in $HOME.

Memory Limit

The Linux system of the front-end nodes has 32 GB of main memory.
Default user limit: To prevent overloading the memory, the sessions have a hardlimit of 3 GB each.

Limits can be checked with the command:

ulimit -v (for memory) or

ulimit -a (for all limits)
Check for: virtual memory (kbytes, -v)
The limit specification is in KBytes.

Programming environment, modules and libraries

The persistent settings of the shell environment are governed by the content of .bashrc , .profile or scripts sourced from within these files. Please use these files for storing your personal settings.

The common programming environment is maintained with the concept of software modules in directory /usr/local and /bgsys/local. The framework provides a set of installed libraries and applications (including multiple-version support) and an easy to use interface (module command) to set up the correct shell environment (see also the (May 2011) slides: module setup and compiler).


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