ARSC HPC Users' Newsletter 327, October 21, 2005

NASA Blue Marble Data Available From ARSC

On Thursday, October 13, NASA announced a new release of their "Blue Marble" dataset. These new images consist of cloudless scenes from space of the entire world, built from mosaics of satellite imagery.

The University of Alaska Fairbanks was one of only a few locations to distribute these new data. Prof. Matt Nolan of the Water and Environmental Research Center at UAF provided the NASA data, which ARSC made available for download. The data consist of 170GB of NASA imagery, plus custom images for the "EarthSLOT" viewer.

Here are links to download the data:

  1. Images: (Links and redirects to: or )

  2. NASA's Information:

  3. EarthSLOT viewer:

The files are available in different formats, and some are quite large. The 8km resolution JPG and PNG files will display in virtually any graphics program, such as a Web browser. Larger files might require special-purpose software to view.

Reminder: Purging of $WRKDIR to Resume on Halloween

As previously announced, ARSC will resume daily automated purging of the $WRKDIR file systems, on October 31, 2005. ARSC is lengthening its traditional purge period of 10 days three-fold, to 30 days. Commencing October 31st, the purger will run every day, and each day, files thirty (30) days old or older (based on access time) will be deleted.

We encourage you to carefully consider all your files on $WRKDIR. Presumably, you've been backing all valuable files up to $ARCHIVE all along, but you might double-check that your backups are complete. In addition, we encourage you to intentionally delete files which you know are not valuable.

By cleaning up in advance, you shouldn't have any surprises, and it will make the initial run of the purger a little easier, as it'll have fewer files to search.

What Files are Subject to Purging? Run: "getPurgable"

ARSC users can run the "getPurgable" script to get a listing of files subject to purging. For help, specify the "-h" option:

$ getPurgable -h

A default run, like this:

$ getPurgable

shows which files are 30 days old or older in the $WRKDIR file system, and thus subject to deletion on the next daily run of the purger. (If you have accounts on multiple ARSC systems, keep in mind that the script only checks the machine on which it is run.)

For more on ARSC's storage policies and infrastructure, see:

X1: Programming Environment Available

The latest X1 programming environment was installed as on Wednesday. This fixes some problems, and may improve optimization for some codes. Users are encouraged to try it and provide feedback.

To access the new environment, use the "module switch" command:

module switch PrgEnv

To be sure you're compiling with, add the "-V" options to your ftn, cc, or CC command line, and the compiler will print version information.

Your Own Personal SSH Configuration File

The ssh suite of tools allow users to specify many options in a local configuration file. This allows a user to extend the system-wide ssh settings and reduce the number of options used on the command line. When a configuration file called "config" is found in your ~/.ssh directory, the options in that file will be used by ssh and other ssh family tools (such as scp and sftp).

The configuration file can specify default usernames, X11 options, verbosity, machine aliases, and more.

Here's a simple configuration file which enabled X11 forwarding and trusted X11 connections.

  pisces 1% cat ~/.ssh/config
  ForwardX11 yes
  ForwardX11Trusted yes

These options will be used for every connection and are equivalent to using "ssh -X -Y". However, the config file can specify options on a host by host basis. This can be useful if your username varies by location or if the options you use vary from system to system.

Below is another example which:

  • specifies a default username and enables X11 forwarding for hosts in the domain.
  • Disables X11 forwarding for all other hosts.

  pisces 2% cat ~/.ssh/config
  Host *
  User username
  ForwardX11 yes
  ForwardX11Trusted yes

  Host *
  ForwardX11 no
  ForwardX11Trusted no

Options are associated with the preceding "Host" statement. A little investigation shows that, in the case of duplicate successful pattern matches, ssh uses the first found. In the example above the "Host *" matches any host not previously matched.

The Host keyword can also be used to create an alias to a machine when used in conjunction with the "HostName" keyword. The "HostName" keyword specifies the real name (or IP address) of the system. Below is an example which creates an alias "ice" for "". E.g.:

  pisces 2% cat ~/.ssh/config
  Host ice
  User username
  ForwardX11 yes
  ForwardX11Trusted yes

With the options above a typical ssh command would go from:

  ssh -X -Y

  ssh ice

There are a number of other ssh config file options. See: "man ssh_config" for details.

SECURITY CONCERNS: Because the "config" file contains login related information, we recommend that you never add "group" or "other" permissions to your ~/.ssh/config file or the ~/.ssh directory.

As outlined in the user security policies, it is a requirement on ARSC systems that "group" and "other" access be denied.

Quick-Tip Q & A

A:[[ My program produces output in NetCDF format.  Are there any 
  [[ utilities available that will let me visualize my NetCDF data?  

  There are two netcdf viewers that I have tried.  These
  tools are perfect for taking a quick look your data, but
  may not be appropriate for presentation quality graphics.
  * ncview is a simple and fast netcdf viewer available on ARSC SGIs,
  iceberg and iceflyer.
  For more details see:

  *  PanoPly is a Java based netcdf viewer from NASA which can runs
  on a number of Operating Systems (including Mac OS X, Windows,
  and UNIX systems with a java interpreter).  In my experience it seems
  a bit slower than ncview, however it more than makes up for this by
  having a number of useful features including: a wide variety of projections,
  color schemes, and export options.
  For more details see:
Q: I love vim's syntax highlighting, but, to save my eyes, I always work
   with light text on a dark background.  Unfortunately, vim uses dark
   blue for C comments and they practically disappear. (So, of course, I
   end up burning my eyes out squinting and getting too close!)

   Is there some way to change vim's colors for syntax highlighting?

[[ Answers, Questions, and Tips Graciously Accepted ]]

Current Editors:
Ed Kornkven ARSC HPC Specialist ph: 907-450-8669
Kate Hedstrom ARSC Oceanographic Specialist ph: 907-450-8678
Arctic Region Supercomputing Center
University of Alaska Fairbanks
PO Box 756020
Fairbanks AK 99775-6020
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