Access and Environment#

SSH Login#

The Secure Shell (SSH) protocol is used to access nodes on Levante. SSH client programs are available for all major operating systems. To access one of the Levante login nodes you can use the following command:

ssh -X <userid>

in which <userid> must be replaced by your individual user account.

Levante host key fingerprints#

When you first connect to Levante, your ssh client will not be able to establish the login node’s authenticity. Any of the following fingerprints is valid for Levante.:


After having logged into Levante, you will find yourself on one of login nodes: levante[0-6]. The login nodes serve as an interface to the compute nodes of the HPC cluster. They are intended for file editing and compilation of source code, as well as for submission, monitoring and canceling of batch jobs. They can also be used for simple and not time nor memory intensive serial processing tasks.

Not more than 10% of a login node’s memory can be used by one user. Any process which exceeds this limit will be killed by the system.


All DKRZ systems are managed by a central directory service (LDAP). The password can be changed through the user and project portal. A user defined password must contain at least eight nonblank characters and has to be a combination of upper and lowercase letters, numbers and special characters. Additional checks are made to ensure that the password is not in a dictionary and not overly simple. The online service will give you detailed error messages if and why a new password was rejected.

In case you do not remember your password please request a password reset.

Public Key Authentication#

The default password authentication is neither comfortable nor very secure. In order to use public key authentication, you have to generate a key pair and upload the public key to DKRZ. The command for key generation is ssh-keygen. It supports different key types. We recommend ed25519 keys.

ssh-keygen -t ed25519

Please use a strong passphrase to secure your key. By default, this created two files named id_ed25519 and

ls ~/.ssh/

The file ending with .pub has to be uploaded to First press “Add key”

upload a new public key

The public key can be selected from a file by pressing the “Browse” button or pasted directly into the Key input field. Do not select UFTP unless you want to use this key for UFTP exclusively. After pressing “Register key”, the key is uploaded to the server. In order to use it on Levante, you have to provide your LDAP password.

push new keys to LDAP

After that your key should be active and ready to use.

ready to use keys are indicated with a green icon

Levante does not yet support ecdsa-sk or ed25519-sk keys (FIDO).

Key validity#

For most key types, the validity or lifetime of the keys is six weeks. A longer lifetime is allowed for keys using hardware tokes (see below). You should receive an e-mail one day before the key expires. You then have to upload a newly created key to continue using public key authentication. The old key is blocked from further use at DKRZ and cannot be uploaded again.

Managing Multiple SSH Keys#

You may require multiple SSH keys for different computer centers. Reasons for this are added security and the fact that policies for key properties and lifetime may differ from site to site.

To prevent your SSH client from trying out all available keys, you should tell it exactly where to use which key. For this purpose you can create or edit your local configuration file ~/.ssh/config.

Host *
     IdentityFile ~/.ssh/id_ed25519
     IdentitiesOnly yes

This tells ssh to use only the key ~/.ssh/id_ed25519 to log into any host at DKRZ.

Increased security and key lifetime with hardware authenticators#

FIDO2 hardware key

OpenSSH starting with version 8.2 supports FIDO/U2F hardware authenticators or tokens. The use of such tokens increases the security of your ssh-key, as not only the key file (and passphrase) is needed for auth, but you need to touch the token when logging into a system. Because of the increased security, we allow a lifetime of 365 days for SSH keys which work in conjunction with such a token. There are two major requirements for the use of this technology:

  • A recent OpenSSH version, i.e. OpenSSH 8.2 or more recent.

  • A token.

We recommend you to ask your IT department for obtaining one. We recommend FIDO certified tokens, following the U2F or FIDO2 specification, with FIDO2 being more future-proof. At DKRZ, Yubicos YubiKey tokens have proven convenient. The cheaper Yubico “Security Key” model does the job.

Once you have the recent SSH client and a token, you need to create a new ssh-key of type ed25519-sk by running

ssh-keygen -t ed25519-sk

You can upload the public key to following the instructions provided above for classic keys. Do not select UFTP. You should notice the extended lifetime when you upload the public key. For authentication with Levante, the token has to communicate with your local device (via USB, NFC, etc.) and you have to touch it to confirm your presence.


Having two keys, one at your desk, one on your keychain/… has proven convenient. Each token needs a separate SSH key.

OSX: The openssh which comes along with MacPorts (here version 8.4, as of 30 Aug 2021) does not support fido2. A ssh (8.7p1) installed via brew does work.

Default login shell#

The default login shell for new DKRZ users is bash. You can change your login shell to tcsh, zsh etc. using the user and project portal. The settings you would like to use every time you log in can be put into special shell setup files. A login bash shell looks for .bash_profile, .bash_login or .profile in your home directory and executes commands from the first file found. A non-login bash shell or bash subshell reads .bashrc file. Tcsh always reads and executes .tcshrc file (or .cshrc if .tcshrc is not found). If tcsh is invoked as login shell, file .login is sourced additionally. The typical tasks and setting that can be put in shell setup files are for example:

  • Creation of a custom prompt

  • Modification of search path for external commands and programs

  • Definition of environment variables needed by programs or scripts

  • Definition of aliases

  • Execution of commands (e.g. module load <modname>/<version>)

Primary group#

Your primary Unix group will be set to the first project your account is member of. This will not be modified until the project expires. Even if you join other projects, the primary group will stay the same. If you wish to have a different primary group (e.g. you are working most of the time for a different project), you will have to contact DKRZ user support, there is no option to change the primary group on your own.

Module environment#

To cover the software needs of DKRZ users and to maintain different software versions, the DKRZ uses the module environment. Loading a module adapts your environment variables to give you access to a specific set of software and its dependencies. The modulefiles are not organized hierarchically but have internal consistency checks for dependencies and can uniquely be identified by naming convention <modname>/<version>.

Each modulefile is named following the below pattern^^

i.e. the package name is followed by the version of the package, then, if it applies, the MPI implementation (name and version), and the compiler (name and version) used to build the package, for example:


Such long module file names are needed to avoid naming conflicts and to support users in the selection of compatible software variants.


If only the <modname> (i.e. without <version>) is supplied to the module command, the lexicographically highest version or one marked as default explicitly is loaded. In most cases this will result in incompatible software combinations. It is important to ensure that you use modules for required libraries built with the same compiler and MPI that you chose to build your program.

In many cases it is unproblematic to use newer compiler and MPI versions for your program than those used to build libraries in the software tree, if those are compatible.

Users can load, unload and query modules through the module command. The most important module sub-commands are:

  • module avail: Shows the list of all available modules

  • module show <modulefile>: Shows the effect of loading the module <modulefile> on your environment. For a deeper insight into the software dependencies, please use the spack command as described below.

  • module load <modulefile>: Loads selected module; a default or lexicographically highest version is chosen, if only <modname> without <version> is specified

  • module list: Lists all modules currently loaded

  • module rm <modulefile>: Unloads module <modname>/<version>

  • module swap <modulefile1> <modulefile2>: Switches loaded module <modulefile1> to <modulefile2> (mainly used to switch to a different version of software)

  • module purge: Unloads all modules

  • module apropos <keyword>: Scans the available module files for the specified keyword and list all matching modules

For further details, please refer to the manual pages for the module command or use --help option:

$ man module
$ module --help

To use the module command in a script you have to source one of the following files before any invocation of the module command:

# in bash or ksh script
source /sw/etc/profile.levante

# in tcsh or csh script
source /sw/etc/csh.levante

The module avail command provides up-to-date information on installed software packages for which environment modules were generated.

Searching and accessing the software tree with spack#

Apart from the module command there is a command called spack for further investigation of the installed software. In fact it is the package manager which is used by DKRZ to build and maintain the software tree. You can find more documentation at

A proper replacement for module avail is spack find, which represents the most basic information: package name and version as well as compiler used to buid the package. To list all software packages installed on Levante, use:

$ spack find

Let’s use the netcdf-c package to compare module and spack commands:

$ module avail netcdf-c
---------------------------------- /sw/spack-levante/spack/modules -----------------------------------
netcdf-c/4.8.1-gcc-11.2.0                                netcdf-c/4.8.1-openmpi-4.1.2-gcc-11.2.0
netcdf-c/4.8.1-intel-2021.5.0                            netcdf-c/4.8.1-openmpi-4.1.2-intel-2021.5.0
$ spack find netcdf-c
==> 6 installed packages
-- linux-rhel8-zen2 / intel@2021.5.0 ----------------------------
netcdf-c@4.8.1  netcdf-c@4.8.1  netcdf-c@4.8.1

-- linux-rhel8-zen3 / gcc@11.2.0 --------------------------------
netcdf-c@4.8.1  netcdf-c@4.8.1  netcdf-c@4.8.1

netcdf-c has a lot of dependencies and can be built in different ways (serial, parallel, w/o netcdf4, w/o thread safety). module on the other hand does not provide much information on this. In the case of netcdf-c it is possible to inspect the installation with the nc-config tool, but not many package provide such a tool.

First let’s try to seperate the available netcdf-c package from each other. Here the -l option of spack find is useful:

$ spack find -l netcdf-c
==> 6 installed packages
-- linux-rhel8-zen2 / intel@2021.5.0 ----------------------------
f7hh57c netcdf-c@4.8.1  2k3cmu3 netcdf-c@4.8.1  7dq6g2h netcdf-c@4.8.1

-- linux-rhel8-zen3 / gcc@11.2.0 --------------------------------
qk24ypm netcdf-c@4.8.1  6qheqru netcdf-c@4.8.1  xguss5s netcdf-c@4.8.1

Each installed package has a unique alphanumeric string (hash), which can be used to identify this package. The first six characters of the hash are used as part of the installation path. Let’s inspect the first package in the list (f7hh57c). The flags -p and -d will print the path and dependency information:

$ spack find -dp /f7hh57c
==> 1 installed package
-- linux-rhel8-zen2 / intel@2021.5.0 ----------------------------
netcdf-c@4.8.1                  /sw/spack-levante/netcdf-c-4.8.1-f7hh57
    curl@7.61.1                 /usr
    hdf@4.2.15                  /sw/spack-levante/hdf-4.2.15-jvpsue
        libaec@1.0.5            /sw/spack-levante/libaec-1.0.5-gij7yv
        libjpeg-turbo@1.5.3     /usr
        libtirpc@1.2.6          /sw/spack-levante/libtirpc-1.2.6-7laks4
            krb5@1.19.2         /sw/spack-levante/krb5-1.19.2-rteqqi
                openssl@1.1.1g  /usr
        zlib@1.2.11             /usr
    hdf5@1.12.1                 /sw/spack-levante/hdf5-1.12.1-4l5deg
        pkg-config@1.4.2        /usr

In this view you can see each individual runtime dependency and where it is located. This is far more than the module command can do. Obviously this is a serial version of netcdf-c without support for parallel I/O useful for tools like CDO. Please note that the spack hash must be prepended with a slash (/) so that spack can handle it as special input instead of a normal package name.

Let’s check the next one in the list:

$ spack find -dp /2k3cmu3
==> 1 installed package
-- linux-rhel8-zen2 / intel@2021.5.0 ----------------------------
netcdf-c@4.8.1                         /sw/spack-levante/netcdf-c-4.8.1-2k3cmu
    curl@7.61.1                        /usr
    hdf@4.2.15                         /sw/spack-levante/hdf-4.2.15-jvpsue
        libaec@1.0.5                   /sw/spack-levante/libaec-1.0.5-gij7yv
        libjpeg-turbo@1.5.3            /usr
        libtirpc@1.2.6                 /sw/spack-levante/libtirpc-1.2.6-7laks4
            krb5@1.19.2                /sw/spack-levante/krb5-1.19.2-rteqqi
                openssl@1.1.1g         /usr
        zlib@1.2.11                    /usr
    hdf5@1.12.1                        /sw/spack-levante/hdf5-1.12.1-tvymb5
        numactl@2.0.14                 /sw/spack-levante/numactl-2.0.14-6yawk5
        openmpi@4.1.2                  /sw/spack-levante/openmpi-4.1.2-yfwe6t
            knem@         /opt/knem-
            libevent@2.1.8             /sw/spack-levante/libevent-2.1.8-mjzu6s
            openssh@8.0p1              /usr
            pmix@3.2.1                 /sw/spack-levante/pmix-3.2.1-xut2g3
                hwloc@2.6.0            /sw/spack-levante/hwloc-2.6.0-43fbvn
                    libpciaccess@0.16  /sw/spack-levante/libpciaccess-0.16-knievr
                    libxml2@2.9.7      /usr
                    ncurses@6.2        /sw/spack-levante/ncurses-6.2-qam5nn
            slurm@20.11.7              /usr
            ucx@1.12.0                 /sw/spack-levante/ucx-1.12.0-nlas56
                rdma-core@35.0         /usr
        pkg-config@1.4.2               /usr
    parallel-netcdf@1.12.2             /sw/spack-levante/parallel-netcdf-1.12.2-mc24h4

This installation of netcdf is parallel and supports hdf4 and hdf5 with szip compression. This installation is useful for a climate or NWP model if you want to build it using the Intel compiler and the Open MPI library.

These differences in building a package are called variants and can printed with the -v option:

$ spack find -lv /2k3cmu3
==> 1 installed package
-- linux-rhel8-zen2 / intel@2021.5.0 ----------------------------
2k3cmu3 netcdf-c@4.8.1+dap~fsync+hdf4~jna+mpi+parallel-netcdf+pic+shared

Instead of using hash 2k3cmu3 it is possible to identify a package by its name, version (@), compiler (%), variant (+, -, ~), and dependencies (^), for example:

$ spack find -p netcdf-c@4.8.1 +mpi +parallel-netcdf +shared %intel@2021.5.0
==> 2 installed packages
-- linux-rhel8-zen2 / intel@2021.5.0 ----------------------------
netcdf-c@4.8.1  /sw/spack-levante/netcdf-c-4.8.1-2k3cmu
netcdf-c@4.8.1  /sw/spack-levante/netcdf-c-4.8.1-7dq6g2

$ spack find -p netcdf-c +mpi %intel@2021.5.0 ^openmpi
==> 1 installed package
-- linux-rhel8-zen2 / intel@2021.5.0 ----------------------------
netcdf-c@4.8.1  /sw/spack-levante/netcdf-c-4.8.1-2k3cmu

In case you are only interested in the installation prefix of a given package, you can use spack find --format='{prefix}'

$ spack find --format='{prefix}' /2k3cmu3

Note, that modulefiles are not generated for every installed software package on Levante. The easiest way to add a package (without an existing modulefile) to the user environment is to use the spack load command, for example:

$ spack find bison
==> 2 installed packages
-- linux-rhel8-zen2 / intel@2021.5.0 ----------------------------

-- linux-rhel8-zen3 / gcc@11.2.0 --------------------------------

$ spack load bison%gcc
$ which bison

$ spack load xterm
$ which xterm

To remove packages from the user environment, the spack unload command can be used:

$ spack unload bison xterm

Loading software packages with the spack load command modifies a number of environment variables, such as PATH, LD_LIBRARY_PATH, MANPATH, PKG_CONFIG_PATH etc. To see changes that will be introduced into your environment by loading a software package with spack, you can use the -sh option:

spack load --sh bison%gcc

To list packages loaded into your environment with spack load, you can use

spack find --loaded

Please have a look into the official documentation of spack for further information.