.\"	$NetBSD: access.2,v 1.7 1995/02/27 12:31:44 cgd Exp $
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.\"     @(#)access.2	8.2 (Berkeley) 4/1/94
.\"
.Dd April 1, 1994
.Dt ACCESS 2
.Os BSD 4
.Sh NAME
.Nm access
.Nd check access permissions of a file or pathname
.Sh SYNOPSIS
.Fd #include <unistd.h>
.Ft int
.Fo access
.Fa "const char *path"
.Fa "int amode"
.Fc
.Sh DESCRIPTION
The
.Fn access
function checks the accessibility of the
file named by
.Fa path
for the access permissions indicated by
.Fa amode .
The value of
.Fa amode
is the bitwise inclusive OR of the access permissions to be
checked
.Pf ( Dv R_OK
for read permission,
.Dv W_OK
for write permission and
.Dv X_OK
for execute/search permission) or the existence test,
.Dv F_OK .
All components of the pathname
.Fa path
are checked for access permissions (including
.Dv F_OK ) .
.Pp
The real user ID is used in place of the effective user ID
and the real group access list
(including the real group ID) are
used in place of the effective ID for verifying permission.
.Pp
Even if a process has appropriate privileges and indicates success for
.Dv X_OK ,
the file may not actually have execute permission bits set.
Likewise for
.Dv R_OK
and
.Dv W_OK .
.Sh RETURN VALUES
If
.Fa path
cannot be found
or if any of the desired access modes would not be granted,
then a -1 value is returned and the global integer variable
.Va errno
is set to indicate the error.
Otherwise, a 0 value is returned.
.Sh ERRORS
Access to the file is denied if:
.Bl -tag -width Er
.\" ==========
.It Bq Er EACCES
Permission bits of the file mode do not permit the requested access,
or search permission is denied on a component of the path prefix.
.Pp
The owner of a file has permission checked
with respect to the ``owner'' read, write, and execute mode bits,
members of the file's group other than the owner have permission checked
with respect to the ``group'' mode bits,
and all others have permissions checked
with respect to the ``other'' mode bits.
.\" 
.\" ==========
.It Bq Er EFAULT
.Fa Path
points outside the process's allocated address space.
.It Bq Er EINVAL
An invalid value was specified for
.Ar amode .
.\" ==========
.It Bq Er EIO
An I/O error occurred while reading from or writing to the file system.
.\" ==========
.It Bq Er ELOOP
Too many symbolic links were encountered in translating the pathname.
.\" ==========
.It Bq Er ENAMETOOLONG
A component of a pathname exceeded 
.Dv {NAME_MAX}
characters, or an entire path name exceeded 
.Dv {PATH_MAX}
characters.
.\" ==========
.It Bq Er ENOENT
The named file does not exist.
.\" ==========
.It Bq Er ENOTDIR
A component of the path prefix is not a directory.
.\" ==========
.It Bq Er EROFS
Write access is requested for a file on a read-only file system.
.\" ==========
.It Bq Er ETXTBSY
Write access is requested for a pure procedure (shared text)
file that is presently being executed.
.El
.Sh SEE ALSO
.Xr chmod 2 ,
.Xr stat 2
.Sh STANDARDS
The
.Fn access
function conforms to 
.St -p1003.1-90 .
.Sh CAVEAT
.Fn Access
is a potential security hole and
should never be used.