[2][3] A filesystem ACL is a data structure (usually a table) containing entries that specify individual user or group rights to specific system objects such as programs, processes, or files.
The privileges or permissions determine specific access rights, such as whether a user can read from, write to, or execute an object.
[6] The POSIX.1e/POSIX.2c drafts were withdrawn in 1997 due to participants losing interest for funding the project and turning to more powerful alternatives such as NFSv4 ACL.
[8] Most of the Unix and Unix-like operating systems (e.g. Linux since 2.5.46 or November 2002,[9] FreeBSD, or Solaris) support POSIX.1e ACLs (not necessarily draft 17).
Examples include AIX, FreeBSD,[10] Mac OS X beginning with version 10.4 ("Tiger"), or Solaris with ZFS filesystem,[11] support NFSv4 ACLs, which are part of the NFSv4 standard.
[16] Microsoft's Active Directory service implements an LDAP server that stores and disseminates configuration information about users and computers in a domain.
[17] Active Directory extends the LDAP specification by adding the same type of access-control list mechanism as Windows NT uses for the NTFS filesystem.
[18] On some types of proprietary computer hardware (in particular, routers and switches), an access-control list provides rules that are applied to port numbers or IP addresses that are available on a host or other layer 3, each with a list of hosts and/or networks permitted to use the service.
Access-control lists can generally be configured to control both inbound and outbound traffic, and in this context they are similar to firewalls.