What is the difference between the system group and netgroup (at least on ubuntu)?
"System groups" (often just "groups") contain users, and are one of the basic security concepts in UNIX and many other operating systems. Each user belongs to a primary group and any number of secondary groups; a group, like a user, can be allowed to access or modify certain files and directories using the usual
"Netgroups", on the other hand, are part of NIS/YP directory services system used only in Unix-like systems. A netgroup contains entries in the form
 Other operating systems may allow more advanced configurations; e.g. Windows NT supports groups as group members.