ACLs
From Linux NFS
Useful references:
rfc3530 (especially section 5.11)] POSIX draft ACLs: POSIX ACLs aren't really POSIX--they were never accepted--but some variation of them is implemented on many operating systems, including Linux. The Linux man pages, specifically, acl(5), setfacl(1), getfacl(1), and setxattr(2). The POSIX<->NFSv4 mapping draft, which explains how we map between POSIX and NFSv4 ACLs.