NetBSD/lib/libc/sys/access.2

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.\"     @(#)access.2	8.2 (Berkeley) 4/1/94
.\"
.Dd April 1, 1994
.Dt ACCESS 2
.Os
.Sh NAME
.Nm access
.Nd check access permissions of a file or pathname
.Sh LIBRARY
.Lb libc
.Sh SYNOPSIS
.Fd #include \*[Lt]unistd.h\*[Gt]
.Ft int
.Fn access "const char *path" "int mode"
.Sh DESCRIPTION
The
.Fn access
function checks the accessibility of the
file named by
.Fa path
for the access permissions indicated by
.Fa mode .
The value of
.Fa mode
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
If a process has super-user privileges and indicates success for
.Dv R_OK
or
.Dv W_OK .
the file may not actually have read or write permission bits set.
If a process has super-user privileges and indicates success for
.Dv X_OK ,
at least one of the user, group, or other execute bits is set.
(However, the file may still not be executable.  See
.Xr execve 2 . )
.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; otherwise
a 0 value is returned.
.Sh ERRORS
Access to the file is denied if:
.Bl -tag -width Er
.It Bq Er ENOTDIR
A component of the path prefix is not a directory.
.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 ELOOP
Too many symbolic links were encountered in translating the pathname.
.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 presently being executed.
.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.  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 EIO
An I/O error occurred while reading from or writing to the file system.
.El
.Sh SEE ALSO
.Xr chmod 2 ,
.Xr execve 2 ,
.Xr stat 2
.Sh STANDARDS
The
.Fn access
function conforms to
.St -p1003.1-90 .
.Sh BUGS
.Fn access
is a potential security hole and
should never be used.