Access Con­trol List

An Access Con­trol List (ACL ) is a list of user per­mis­sions for a file, folder, or other object. It defines whether users and user groups can access the object and what oper­a­tions they are allowed to per­form on it. These oper­a­tions typ­i­cally include read, write, and exe­cute.

ACLs pro­vide a straight­for­ward method of man­ag­ing file and folder per­mis­sions. They are used by most oper­at­ing sys­tems, includ­ing Win­dows, Mac OS X, and Linux/Unix sys­tems.

For exam­ple, if an ACL spec­i­fies read-only access for a spe­cific user of a file, that user will be able to open the file, but can­not write, nor exe­cute the file, thus not chang­ing its con­tents.

While ACLs are typ­i­cally hid­den from the user, they can often be mod­i­fied using a graph­i­cal inter­face. On Unix sys­tems, ACLs can be edited using the chmod com­mand.