Permission
http://linux.vbird.org/linux_basic/0210filepermission.php#filepermission
SUID/SGID/Sticky Bit
http://linux.vbird.org/linux_basic/0220filemanager.php#fileperm
ACL
http://www.redhat.com/docs/manuals/enterprise/RHEL-5-manual/File_Systems/ch-acls.html
http://linux.vbird.org/linux_server/0240network-secure-1.php#acl
Selinux
http://www.redhat.com/docs/manuals/enterprise/RHEL-4-Manual/selinux-guide/
http://www.redhat.com/docs/manuals/enterprise/RHEL-5-manual/Security_And_Authentication/index.html