Access and user environment

Logging in | Shell | Environment modules | Changing UNIX groups

Individuals who have user accounts that are associated with valid, allocated projects can log in to Yellowstone by following the procedure described below.

If you don't have a user account, see User accounts and access.

If you are not associated with a valid, allocated project, see Allocations to learn about opportunities for which you might qualify.

Logging in

Centralizing the login nodes makes for efficient workflow. Users can submit a set of dependent, chained batch jobs to run without their intervention.

The Yellowstone HPC system and the Geyser and Caldera analysis and visualization clusters share login nodes.

Once you log in to, you will be able to schedule jobs to run through any queue or start an interactive session on Geyser or Caldera.

Centralizing the login nodes provides significant benefits by making workflow more efficient. For example, you can submit a set of dependent, chained batch jobs to run without your intervention:

  • one on Geyser that reads and preprocesses a data set from our Research Data Archive;
  • then a large-scale simulation on Yellowstone using that input data;
  • followed by post-processing on Geyser;
  • then another to generate a set of visualizations on Caldera.

See Submitting dependent jobs for a sample script.

Use SSH to log in

To log in, use ssh as follows:

ssh -X -l username

You can use this shorter command if your UCAR username is the same as the username on your local computer:

ssh -X

After entering your username, you will be prompted to enter a "Token_Response." Generate that response with your YubiKey token or CRYPTOCard keypad.

The first time you log in, or before you want to run jobs on the Geyser or Caldera clusters, install SSH keys on Yellowstone so you can submit jobs without having to authenticate each time.


The default login shell for new users is tcsh.

To confirm which shell is your default shell, enter:

echo $SHELL

Sample output:


If you want to change your default login shell, you can do that through the CISL Systems Accounting Manager (SAM).

Environment modules

CISL makes extensive use of environment modules to help you manage your computing environment. The module utility helps you quickly identify software packages that are available on the system, ensures that only compatible packages are loaded, and helps you modify your environment easily when you need to.

The system loads several modules by default to define key components of the user environment. Only experienced users should unload these default modules, which are:

  1) intel/12.1.5       3) ncarcompilers/1.0    5) netcdf/4.3.0
  2) ncarbinlibs/1.1    4) ncarenv/1.0

With the modules utility managing the complex combinations of variables that you otherwise would have to remember, you can compile and run jobs more efficiently, with fewer errors, and make better use of your allocated resources.

Our Environment modules page provides additional information and examples of how to use several basic module commands.

Changing UNIX groups

The preferred way to change your default primary UNIX group is through the Systems Accounting Manager (SAM). Changes made there typically take effect the next business day.

If you need to change your current effective group, use the sg command with the name of the new group.

sg new_groupname

The new name will persist until you change it again or start a new session.