acl(3)

NAME

acl - introduction to the POSIX.1e ACL security API

LIBRARY

Standard C Library (libc, -lc)

SYNOPSIS

#include <sys/types.h>
#include <sys/acl.h>

DESCRIPTION

FreeBSD permits file systems to export Access Control Lists

via the VFS,
and provides a library for userland access to and manipula

tion of these
ACLs. Not all file systems provide support for ACLs, and

some may
require that ACL support be explicitly enabled by the admin

istrator. The
library calls include routines to allocate, duplicate, re

trieve, set, and
validate ACLs associated with file objects. As well as the

POSIX.1e routines, there are a number of non-portable extensions defined

that allow
for alternative ACL semantics than the POSIX.1e semantics,

such as AFS,
NTFS, Coda, and NWFS semantics. Where routines are non

standard, they
are suffixed with _np to indicate that they are not

portable.

POSIX.1e describes a set of ACL manipulation routines to

manage the contents of ACLs, as well as their relationships with files;

almost all of
these support routines are implemented in FreeBSD.

Available functions, sorted by behavior, include:

acl_add_perm()

This function is described in acl_add_perm(3), and

may be used to
add permissions to a permission set.

acl_calc_mask()

This function is described in acl_calc_mask(3), and

may be used
to calculate and set the permissions associated with

the ACL_MASK
entry.

acl_clear_perms()

This function is described in acl_clear_perms(3),

and may be used
to clear all permissions from a permission set.

acl_copy_entry()

This function is described in acl_copy_entry(3), and

may be used
to copy the contents of an ACL entry.

acl_create_entry()

This function is described in acl_create_entry(3),

and may be
used to create an empty entry in an ACL.

acl_delete_def_file(), acl_delete_def_link_np(),

acl_delete_fd_np(),

acl_delete_file_np(), acl_delete_link_np() These functions are described in acl_delete(3), and

may be used
to delete ACLs from file system objects.

acl_delete_entry()

This function is described in acl_delete_entry(3),

and may be
used to delete an entry from an ACL.

acl_delete_perm()

This function is described in acl_delete_perm(3),

and may be used
to delete permissions from a permset.

acl_dup()

This function is described in acl_dup(3), and may be

used to
duplicate an ACL structure.

acl_free()

This function is described in acl_free(3), and may

be used to
free userland working ACL storage.

acl_from_text()

This function is described in acl_from_text(3), and

may be used
to convert a text-form ACL into working ACL state,

if the ACL has
POSIX.1e semantics.

acl_get_entry()

This function is described in acl_get_entry(3), and

may be used
to retrieve a designated ACL entry from an ACL.

acl_get_fd(), acl_get_fd_np(), acl_get_file(),

acl_get_link_np()

These functions are described in acl_get(3), and may

be used to
retrieve ACLs from file system objects.

acl_get_permset()

This function is described in acl_get_permset(3),

and may be used
to retrieve a permset from an ACL entry.

acl_get_qualifier()

This function is described in acl_get_qualifier(3),

and may be
used to retrieve the qualifier from an ACL entry.

acl_get_tag_type()

This function is described in acl_get_tag_type(3),

and may be
used to retrieve the tag type from an ACL entry.

acl_init()

This function is described in acl_init(3), and may

be used to
allocate a fresh (empty) ACL structure.

acl_set_fd(), acl_set_fd_np(), acl_set_file(),

acl_set_link_np()

These functions are described in acl_set(3), and may

be used to
assign an ACL to a file system object.

acl_set_permset()

This function is described in acl_set_permset(3),

and may be used
to set the permissions of an ACL entry from a

permset.

acl_set_qualifier()

This function is described in acl_set_qualifier(3),

and may be
used to set the qualifier of an ACL.

acl_set_tag_type()

This function is described in acl_set_tag_type(3),

and may be
used to set the tag type of an ACL.

acl_to_text()

This function is described in acl_to_text(3), and

may be used to
generate a text-form of a POSIX.1e semantics ACL.

acl_valid(), acl_valid_fd_np(), acl_valid_file_np(),

acl_valid_link_np()

These functions are described in acl_valid(3), and

may be used to
validate an ACL as correct POSIX.1e-semantics, or as

appropriate
for a particular file system object regardless of

semantics.

Documentation of the internal kernel interfaces backing

these calls may
be found in acl(9). The syscalls between the internal in

terfaces and the
public library routines may change over time, and as such

are not documented. They are not intended to be called directly without

going
through the library.

SEE ALSO

getfacl(1), setfacl(1), acl_add_perm(3), acl_calc_mask(3),
acl_clear_perms(3), acl_copy_entry(3), acl_create_entry(3),
acl_delete_entry(3), acl_delete_perm(3), acl_dup(3),

acl_free(3),
acl_from_text(3), acl_get(3), acl_get_permset(3),

acl_get_qualifier(3),
acl_get_tag_type(3), acl_init(3), acl_set(3),

acl_set_permset(3),
acl_set_qualifier(3), acl_set_tag_type(3), acl_to_text(3),

acl_valid(3),
posix1e(3), acl(9)

STANDARDS

POSIX.1e assigns security labels to all objects, extending

the security
functionality described in POSIX.1. These additional labels

provide
fine-grained discretionary access control, fine-grained ca

pabilities, and
labels necessary for mandatory access control. POSIX.2c de

scribes a set
of userland utilities for manipulating these labels.

POSIX.1e is described in IEEE POSIX.1e draft 17. Discussion

of the draft
continues on the cross-platform POSIX.1e implementation

mailing list. To
join this list, see the FreeBSD POSIX.1e implementation page

for more
information.

HISTORY

POSIX.1e support was introduced in FreeBSD 4.0; FreeBSD 5.0

was the first
version to include a complete ACL implementation based on

extended
attributes for the UFS and UFS2 file systems.

The getfacl(1) and setfacl(1) utilities describe the user

tools that permit direct manipulation of complete file ACLs.

AUTHORS

Robert N M Watson

BSD December 18, 2002

BSD