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Issue description   When discussing the sgid bit with directories, we have watered this down over the years in the constantly changing umask situation.  We can avoid any umask concerns and still get collaboration or shared directories to function, and I have been told by students this is a feature that they use a lot.  We just need to add that for the setgid to have any practical purpose, it needs to be paired with default ACL:

setfacl -m d:g::rwx <directory>

It is a simple command but without it the sgid bit is in any practical sense meaningless.

This produces a true collaboration directory where all users collaborate on all files and can edit files within the directory even if they do not own the file.

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