Linux Access Control Lists library (libacl, -lacl).  The function
returns if the file identified by the argument is associated with
an extended access ACL. The function returns if the file does not
have an extended access ACL.  An extended ACL is an ACL that con‐
tains  entries other than the three required entries of tag types
ACL_USER_OBJ, ACL_GROUP_OBJ and ACL_OTHER.  If the result of  the
function  for  a  file  object is then the ACL defines no discre‐
tionary access rights other than those  already  defined  by  the
traditional  file permission bits.  Access to the file object may
be further restricted by other mechanisms, such as Mandatory  Ac‐
cess  Control  schemes.  The  system  call  can  be used to check
whether a given type of access to a file object would be granted.
If successful, the function returns if the file object identified
by has an extended access ACL, and if the file object  identified
by  does not have an extended access ACL. Otherwise, the value is
returned and the global variable is set to  indicate  the  error.
If  any  of  the following conditions occur, the function returns
and sets to the corresponding value: The argument is not a  valid
file descriptor.  The file system on which the file identified by
is  located does not support ACLs, or ACLs are disabled.  This is
a non‐portable, Linux specific extension to the ACL  manipulation
functions defined in IEEE Std 1003.1e draft 17 (“POSIX.1e”, aban‐
doned).  Written by