Data Sharing on Hoffman2

There are a few things to keep in mind. Users on the cluster are organized into groups. Every user belongs to a primary group and may be in several secondary groups. You can see the list of groups you belong to with the groups command, e.g.

joebruin@login2:~$ groups joebruin
joebruin : web gpu 

In the previous example, you see my primary group is web (first in the list), and I only belong to one secondary group, gpu.  A user can belong to many groups, but a file or directory can be owned by only one owner and one group. Group membership can give you access to files and directories belonging to that group.

So, in order to share data, you must have a common group to which both users belong. For example, if I want to share a folder with Hoffman2 user, sambruin, I would check for a common group that we both belong to with the groups command:

joebruin@login2:~$ groups $USER sambruin
joebruin : web gpu
sambruin : acct gpu

In this example, gpu is a group we’re both members of, so I could share data as long as it’s owned by the group, “gpu” and the permissions on the directory and files give the group members access. Group ownership does not imply group access; you must set the file access permissions so your group can use the files. For that you would use the chown and chmod commands, or newgrp to change your working group in your current shell.