Sharing files

W&M HPC systems use standard Unix file permissions. See https://www.nersc.gov/users/data-and-file-systems/unix-file-permissions/ for a brief overview.

On our systems, a user's primary group has traditionally been set based on the user's affiliation; e.g. an undergraduate in the mathematics department was assigned mathu. If sharing within your primary group is insufficient, supplementary groups like vimsmf and littlebaby are configured as needed. Contact IT/HPC if you need a group to be created or modified.

After a group is created or modified, users are responsible for assigning files to groups and setting appropriate permissions using the chgrp and chmod commands, e.g.

  chgrp -R GROUP DIRECTORY
  chmod -R g+rX DIRECTORY

Since we will not have changed your primary group, files you create will not be assigned to the new group by default. One can reduce the amount of times one has to chgrp files and directories by placing directories in "setgid" mode:

  chmod g+s DIRECTORY

which causes new files in DIRECTORY to be assigned the directory's group instead of the user's primary group.

Note, however, that the default umask on W&M HPC systems is 077, which generally causes files you create to be accessible only by you, regardless of the file's group, under the philosophy that unintentionally limiting access is better than unintentionally providing it. You can set a different umask in your .cshrc file, after the line

  source /usr/local/etc/sciclone.cshrc

or

  source /usr/local/etc/chesapeake.cshrc

using the umask command, e.g.

  umask 027

which will change the default for new files to also granting read access to the file's group. See the linked overview for more information about umask, chmod, and setgid directories.