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.\" $FreeBSD: head/share/man/man9/acl.9 287445 2015-09-04 00:14:20Z delphij $
.\"
.Dd January 18, 2022
.Dt ACL 9
.Os
.Sh NAME
.Nm acl
.Nd virtual file system access control lists
.Sh SYNOPSIS
.In sys/param.h
.In sys/vnode.h
.In sys/acl.h
.Pp
In the kernel configuration file:
.Cd "options UFS_ACL"
.Sh DESCRIPTION
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
.Fa type
field of the appropriate vnode ACL calls:
.Xr VOP_ACLCHECK 9 ,
.Xr VOP_GETACL 9 ,
and
.Xr VOP_SETACL 9 .
.Pp
Currently, each ACL is represented in-kernel by a fixed-size
.Vt acl
structure, defined as follows:
.Bd -literal -offset indent
struct acl {
        unsigned int            acl_maxcnt;
        unsigned int            acl_cnt;
        int                     acl_spare[4];
        struct acl_entry        acl_entry[ACL_MAX_ENTRIES];
};
.Ed
.Pp
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.
In this implementation, the
.Vt acl_maxcnt
field is always set to
.Dv ACL_MAX_ENTRIES .
.Pp
Each individual ACL entry is of the type
.Vt acl_entry_t ,
which is a structure with the following members:
.Bl -tag -width 2n
.It Vt acl_tag_t Va ae_tag
The following is a list of definitions of ACL types
to be set in
.Va ae_tag :
.Pp
.Bl -tag -width ".Dv ACL_UNDEFINED_FIELD" -offset indent -compact
.It Dv ACL_UNDEFINED_FIELD
Undefined ACL type.
.It Dv ACL_USER_OBJ
Discretionary access rights for processes whose effective user ID
matches the user ID of the file's owner.
.It Dv ACL_USER
Discretionary access rights for processes whose effective user ID
matches the ACL entry qualifier.
.It Dv 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.
.It Dv ACL_GROUP
Discretionary access rights for processes whose effective group ID
or any supplemental groups
match the ACL entry qualifier.
.It Dv ACL_MASK
The maximum discretionary access rights that can be granted
to a process in the file group class.
This is only valid for POSIX.1e ACLs.
.It Dv ACL_OTHER
Discretionary access rights for processes not covered by any other ACL
entry.
This is only valid for POSIX.1e ACLs.
.It Dv ACL_OTHER_OBJ
Same as
.Dv ACL_OTHER .
.It Dv ACL_EVERYONE
Discretionary access rights for all users.
This is only valid for NFSv4 ACLs.
.El
.Pp
Each POSIX.1e ACL must contain exactly one
.Dv ACL_USER_OBJ ,
one
.Dv ACL_GROUP_OBJ ,
and one
.Dv ACL_OTHER .
If any of
.Dv ACL_USER ,
.Dv ACL_GROUP ,
or
.Dv ACL_OTHER
are present, then exactly one
.Dv ACL_MASK
entry should be present.
.It Vt uid_t Va ae_id
The ID of user for whom this ACL describes access permissions.
For entries other than
.Dv ACL_USER
and
.Dv ACL_GROUP ,
this field should be set to
.Dv ACL_UNDEFINED_ID .
.It Vt acl_perm_t Va ae_perm
This field defines what kind of access the process matching this ACL has
for accessing the associated file.
For POSIX.1e ACLs, the following are valid:
.Bl -tag -width ".Dv ACL_WRITE_NAMED_ATTRS"
.It Dv ACL_EXECUTE
The process may execute the associated file.
.It Dv ACL_WRITE
The process may write to the associated file.
.It Dv ACL_READ
The process may read from the associated file.
.It Dv ACL_PERM_NONE
The process has no read, write or execute permissions
to the associated file.
.El
.Pp
For NFSv4 ACLs, the following are valid:
.Bl -tag -width ".Dv ACL_WRITE_NAMED_ATTRS"
.It Dv ACL_READ_DATA
The process may read from the associated file.
.It Dv ACL_LIST_DIRECTORY
Same as
.Dv ACL_READ_DATA .
.It Dv ACL_WRITE_DATA
The process may write to the associated file.
.It Dv ACL_ADD_FILE
Same as
.Dv ACL_ACL_WRITE_DATA .
.It Dv ACL_APPEND_DATA
.It Dv ACL_ADD_SUBDIRECTORY
Same as
.Dv ACL_APPEND_DATA .
.It Dv ACL_READ_NAMED_ATTRS
Ignored.
.It Dv ACL_WRITE_NAMED_ATTRS
Ignored.
.It Dv ACL_EXECUTE
The process may execute the associated file.
.It Dv ACL_DELETE_CHILD
.It Dv ACL_READ_ATTRIBUTES
.It Dv ACL_WRITE_ATTRIBUTES
.It Dv ACL_DELETE
.It Dv ACL_READ_ACL
.It Dv ACL_WRITE_ACL
.It Dv ACL_WRITE_OWNER
.It Dv ACL_SYNCHRONIZE
Ignored.
.El
.It Vt acl_entry_type_t Va ae_entry_type
This field defines the type of NFSv4 ACL entry.
It is not used with POSIX.1e ACLs.
The following values are valid:
.Bl -tag -width ".Dv ACL_WRITE_NAMED_ATTRS"
.It Dv ACL_ENTRY_TYPE_ALLOW
.It Dv ACL_ENTRY_TYPE_DENY
.El
.It Vt acl_flag_t Va ae_flags
This field defines the inheritance flags of NFSv4 ACL entry.
It is not used with POSIX.1e ACLs.
The following values are valid:
.Bl -tag -width ".Dv ACL_ENTRY_DIRECTORY_INHERIT"
.It Dv ACL_ENTRY_FILE_INHERIT
.It Dv ACL_ENTRY_DIRECTORY_INHERIT
.It Dv ACL_ENTRY_NO_PROPAGATE_INHERIT
.It Dv ACL_ENTRY_INHERIT_ONLY
.It Dv ACL_ENTRY_INHERITED
.El
The
.Dv ACL_ENTRY_INHERITED
flag is set on an ACE that has been inherited from its parent.
It may also be set programmatically, and is valid on both files
and directories.
.El
.Sh SEE ALSO
.Xr acl 3 ,
.Xr genfs 9 ,
.Xr genfs_can_access 9 ,
.Xr genfs_can_access_acl_nfs4 9 ,
.Xr genfs_can_access_acl_posix1e 9 ,
.Xr VOP_ACLCHECK 9 ,
.Xr VOP_GETACL 9 ,
.Xr VOP_SETACL 9
.Sh AUTHORS
This manual page was written by
.An Robert Watson .