PDSF is running Scientific Linux 6.2 as it's native operating system, which is not intended for general use. Instead, the chos utility is used to create a Scientific Linux 5.3 environment on both the interactive nodes and in batch. sl53 is the default and is what you will get if you just login without a .chos file.
To automatically select a system version you need to create a file in your home directory named .chos (with the dot at the beginning). In this file you should have one and only one line:
|In your .chos file:||The operating system you get:|
|sl53||64-bit Scientific Linux 5.3|
|sl62||64-bit Scientific Linux 6.2|
When you log in you should have a full, working environment with the system of your choice.
By default your batch jobs will run under the system version you submitted them from. If you want your batch jobs to run under a different CHOS environment from the one you are interactively working in, you can set the CHOS variable to the environment you want while submitting the job. This can be done as follows:
qsub -v CHOS=sl62 script_name
You can switch also "live" between system versions. To do that set the CHOS variable to the path for the system you want to get and then run the "chos" command. For example:
setenv CHOS sl62