File Groups at NERSC

Unix file groups are an important component of effective data management, providing a means to control access to shared data on disk and tape.  At NERSC, file groups are also used to control access to certain computational resources (e.g., batch queues, testbed systems, licensed software).

Overview of File Groups

Every user on a Unix system is a member of one or more file groups, including their primary or default file group.  Every file (or directory) on the system has an owner and an associated file group.  When a user creates a file, the file's associated file group will be the user's default file group.  The user (owner) has the ability to change the associated file group to any of the groups to which the user belongs.  File groups can be defined that allow users to share data with other users who belong to the same groups.

File Groups at NERSC

File group names are limited to eight characters.  A user's default file group is the same as their username.  NERSC users usually belong to several other groups, including groups associated with specific research projects.  For example, consider a NERSC user named "elvis", who is working with the "Big Science" research project.  This project has an allocation on NERSC's MPP systems, controlled by the repository (repo) "bigsci".  Associated with this the repo is the file group "bigsci".  The user (elvis) would then be a member of two file groups, elvis and bigsci.  Because a NERSC user can be a member of more than one research project, such a user would be a member of more than one repo-associated file group.

NERSC PIs, PI Proxies, and Project Managers can manage file group membership with NIM.  Continuing with the example above, if user elvis wants to collaborate with another user "jimi", but does not want other members of bigsci to be able to see the data, the PI for Big Science could create a new file group (for example, "ejdata", for elvis and jimi's data).  The PI would then add elvis and jimi to the ejdata file group.  Those two users could then use "group permissions" on directories and files to share data with one another.  Currently, PIs who wish to create a file group should contact NERSC Consulting.

Useful File Group Commands