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File Permissions on HPCC

The HPCC offers several different types of storage for users. All of these filesystems make use of standard UNIX file permissions. Understanding how standard UNIX permissions and ownership works is an important way to control access to your files.

UNIX users and groups

Every user has a unique username on HPCC systems. This is typically your MSU NetID. Every user is also a member of at least one group. This group is typically the department the user is in (such as cse or plb). An user can be a member of additional groups. To see what groups you are a member of, run the groups command. If you feel you are in the wrong group, please contact HPCC staff.

UNIX file ownership

Every file and directory has two sets of ownership, the user and the group. The user owner is normally set to the user that created the file. Normally, the user owner of a file or directory is the only user that is able to change permissions or group ownership.

The group owner of a file or directory allows a user owner to grant permissions to a group of users for a particular file or directory. The user owner of a file can change the group ownership of a file to any group that they are a member of. Any file created by a user normally defaults to group owner being set to the user's primary group, unless the user or directory owner has changed the behavior (using procedures described here.)

The three types of basic UNIX permissions

Read

Read permission on a file allows the contents of a file to be read. The read permission, when applied to a directory, allows the contents of a directory to be listed. Referred to as "r" in the output of the ls -l command.

Write

Write permission on a file allows the file to be modified or deleted. Write permissions in a directory allow the creation of additional files in that directory. Referred to as "w" in the output of the ls -l command.

Execute

The execute permission allows a file to be run as an executable. When applied to a directory it allows traversal of that directory: the ablility to access files or subdirectories in that directory. Referred to as "x" in the output of the ls -l command.

Other resources

This just covers the basic ideas of UNIX file permissions. In order to work with permissions on the HPCC most effectively, see the page on managing file permissions. Here are some other resources for more in-depth information: