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UNIX/Linux : Access control lists (ACLs) basics
Why we need ACLs ? Every file on any UNIX file will have a owner/group and set of permissions. Imagine a case when multiple users need access to the same file and the users are from different groups. The file access control lists (FACLs) or simply ACLs are the list of additional user/groups and their permission to the file.
How to know when a file has ACL attached to it It is very easy to know when a file has a attached ACL to it. ls -l command would produce a output as show below.
# ls -l -rw-r--r-+ 1 root root 0 Sep 19 14:41 file
Note the + sign at the end of the permissions. This confirms that the file has an ACL attached to it.