:man| Alphabetical   Categories   About us 
ACL (9) | Kernel routines | Unix Manual Pages | :man


acl - virtual file system access control lists


Implementation Notes
See Also


.In sys/param.h
.In sys/vnode.h
.In sys/acl.h

In the kernel configuration file:
.Cd "options UFS_ACL"


Access control lists, or ACLs, allow fine-grained specification of rights for vnodes representing files and directories. However, as there are a plethora of file systems with differing ACL semantics, the vnode interface is aware only of the syntax of ACLs, relying on the underlying file system to implement the details. Depending on the underlying file system, each file or directory may have zero or more ACLs associated with it, named using the type field of the appropriate vnode ACL calls: VOP_ACLCHECK(9), VOP_GETACL(9), and VOP_SETACL(9).

Currently, each ACL is represented in-kernel by a fixed-size
.Vt acl structure, defined as follows:
struct acl {
int acl_cnt;
struct acl_entry acl_entry[ACL_MAX_ENTRIES];

An ACL is constructed from a fixed size array of ACL entries, each of which consists of a set of permissions, principal namespace, and principal identifier.

Each individual ACL entry is of the type
.Vt acl_entry_t , which is a structure with the following members:

Vt acl_tag_t ae_tag
The following is a list of definitions of ACL types to be set in ae_tag:

ACL_USER_OBJ Discretionary access rights for processes whose effective user ID matches the user ID of the file’s owner.
ACL_USER Discretionary access rights for processes whose effective user ID matches the ACL entry qualifier.
ACL_GROUP_OBJ Discretionary access rights for processes whose effective group ID or any supplemental groups match the group ID of the file’s owner.
ACL_GROUP Discretionary access rights for processes whose effective group ID or any supplemental groups match the ACL entry qualifier.
ACL_MASK The maximum discretionary access rights that can be granted to a process in the file group class.
ACL_OTHER Discretionary access rights for processes not covered by any other ACL entry.
ACL_OTHER_OBJ Same as ACL_OTHER. Each ACL entry must contain exactly one ACL_USER_OBJ, one ACL_GROUP_OBJ, and one ACL_OTHER. If any of ACL_USER, ACL_GROUP, or ACL_OTHER are present, then exactly one ACL_MASK entry should be present.
Vt uid_t ae_id The ID of user for whom this ACL describes access permissions.
Vt acl_perm_t ae_perm This field defines what kind of access the process matching this ACL has for accessing the associated file.
ACL_EXECUTE The process may execute the associated file.
ACL_WRITE The process may write to the associated file.
ACL_READ The process may read from the associated file.
ACL_PERM_NONE The process has no read, write or execute permissions to the associated file.


typedef mode_t *acl_permset_t;

/* internal ACL structure */
struct acl {
int acl_cnt;
struct acl_entry acl_entry[ACL_MAX_ENTRIES];

/* external ACL structure */
struct acl_t_struct {
struct acl ats_acl;
int ats_cur_entry;
typedef struct acl_t_struct *acl_t;

* Possible valid values for ae_tag field.
#define ACL_UNDEFINED_TAG 0x00000000
#define ACL_USER_OBJ 0x00000001
#define ACL_USER 0x00000002
#define ACL_GROUP_OBJ 0x00000004
#define ACL_GROUP0x00000008
#define ACL_MASK 0x00000010
#define ACL_OTHER0x00000020

* Possible valid values for acl_type_t arguments.
#define ACL_TYPE_ACCESS 0x00000000
#define ACL_TYPE_DEFAULT 0x00000001
#define ACL_TYPE_AFS 0x00000002
#define ACL_TYPE_CODA 0x00000003
#define ACL_TYPE_NTFS 0x00000004
#define ACL_TYPE_NWFS 0x00000005

* Possible flags in ae_perm field.
#define ACL_EXECUTE 0x0001
#define ACL_WRITE0x0002
#define ACL_READ 0x0004
#define ACL_PERM_NONE 0x0000

* Possible entry_id values for acl_get_entry()

* Undefined value in ae_id field
#define ACL_UNDEFINED_ID ((uid_t)-1)


acl(3), vaccess_acl_posix1e(9), VFS(9), vnaccess(9), VOP_ACLCHECK(9), VOP_GETACL(9), VOP_SETACL(9)


Share this page

     Follow us

Facebook Twitter Google+ LinkedIn

Created by Blin Media, 2008-2013