2.9BSD/usr/man/man2/access.2

.TH ACCESS 2 
.UC
.SH NAME
access \- determine accessibility of file
.SH SYNOPSIS
.B #include <sys/types.h>
.br
.B #include <sys/file.h>
.sp
.B access(name, mode)
.br
.B char *name;
.SH DESCRIPTION
.I Access
checks the given
file
.I name
for accessibility according to
.I mode,
which is FACCESS_READ (read), FACCESS_WRITE (write), or
FACCESS_EXECUTE (execute) or a combination thereof.
Specifying FACCESS_EXISTS
tests whether the directories leading to the file can be
searched and the file exists.
.PP
An appropriate error indication is returned if 
.I name
cannot be found or if any
of the desired access modes would not be granted.
On disallowed accesses
\-1 is returned and the error code is in
.IR errno .
Zero is returned from successful tests.
.PP
The user and group IDs with respect to which permission is checked
are the real UID and GID of the process, so this call is
useful to set-UID programs.
.PP
Notice that it is only access bits that are checked.
A directory may be announced as writable by
.I access,
but an attempt to open it for writing will fail
(although files may be created there);
a file may look executable, but
.I exec
will fail unless it is in proper format.
.SH ERRORS
.I Access
to the file is denied if one or more of the following is true:
.TP 20
[ENOTDIR]
A component of the path prefix is not a directory.
.TP 20
[ENOENT]
Read, write, or execute (search) permission is requested for a null
path name or the named file does not exist.
.TP 20
[EINVAL]
The
.I name
argument contained a non-ASCII byte.
.TP 20
[ELOOP]
Too many symbolic links were encountered in translating the path name.
.TP 20
[EROFS]
Write access is requested for a file on a read-only file system.
.TP 20
[ETXTBSY]
Write access is requested for a pure procedure (shared text) file
that is being executed.
.TP 20
[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.
.TP 20
[EFAULT]
.I Name
points outside the process's allocated address space.
.SH BUGS
The test for execute permission may be successful even though
.I name
is a shared text file which is
currently open for reading and therefore not executable.
The super-user is always granted execute permission even though 1) execute
permission is meaningful only for directories and regular files, and 2)
.I exec
requires that at least one execute mode bit be set for a regular file
to be executable.
.SH SEE ALSO
chmod(2), execve(2), stat(2)
.SH ASSEMBLER
(access = 33.)
.br
.B sys access; name; mode