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3.4.1 Access control entries

An access control list is build of any number of individual access control entries (ACEs). The ACEs has the following general syntax:

 
    acl_type:user/group:permissions

The user or group is sometimes referred to as a key.

For an explanation of ACL types and their use, refer to your local manual page. However, note that for each type of filesystem, there are certain entries which must exist in an ACL. If you are creating a new ACL from scratch, you must specify these. For example, in solaris ACLs you must have entries for user, group and other. Under DFS you need what DFS calls a user_obj, group_obj and an other_obj, and in some cases mask_obj. In cfengine syntax these are called user:*:, other:*: and mask:*:, as described below. If you are appending to an existing entry, you do not have to re-specify these unless you want to change them.

Cfengine can overwrite (replace) or append to one or more ACL entries.

overwrite
method:overwrite is the default. This sets the ACL according to the specified entries which follow. The existing ACL will be overwritten completely.

append
method:append adds or modifies one or more specified ACL entries. If an entry already exists for the specified type and user/group, the specified permission bits will be added to the old permissions. If there is no ACL entry for the given type and user/group, a new entry will be appended.

If the new ACL exactly matches the existing ACL, the ACL is not replaced.

The individual bits in an ACE may be either added subtracted or set equal to a specified mask. The `+' symbol means add, the `-' symbol subtract and `=' means set equal to. Here are some examples:
 
  acltype:id/*:mask

  user:mark:+rx,-w
  user:ds:=r
  user:jacobs:noaccess
  user:forgiven:default

  user:*:rw
  group:*:r
  other:*:r

The keyword noaccess means set all access bits to zero for that user, i.e. remove all permissions. The keyword default means remove the named user from the access crontrol list altogether, so that the default permissions apply. A star/asterisk in the centre field indicates that the user or group ID is implicitly specified as of the owner of the file, or that no ID is applicable at all (as is the case for `other').


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