Quote:
Originally Posted by
popeye
What does being a member of any or all give me that any or all of the rest do not, by way of permission.
Each file on a Unix filesystem belongs to a user and a group.
When you are accessing to the filesystem, you are also having a single user identifier and a single effective group identifier. Run the "id" command to see them.
Each file has also read, write and execute permissions for its owner, its group and others (eg: rwxr-xr--).
If you are the file owner, the first set of permissions apply, here you can read, write and execute the file.
If your current group is the same of the file the second set apply, here you can read and execute the file but not write (modify) it.
Otherwise, the last set apply. You can only read the file.
You change (i.e. login) to a new group with the newgrp command.
ACLs are an alternative, more modern and flexible way to grant attributes to users.