Copyright (c) 1980 Regents of the University of California.
All rights reserved. The Berkeley software License Agreement
specifies the terms and conditions for redistribution.

@(#)access.2 6.1 (Berkeley) 05/09/85

C 4 access - determine accessibility of file

#include <sys/file.h>

#define R_OK 4 /* test for read permission */
#define W_OK 2 /* test for write permission */
#define X_OK 1 /* test for execute (search) permission */
#define F_OK 0 /* test for presence of file */

accessible = access(path, mode)
int accessible;
char *path;
int mode;

Access checks the given file path for accessibility according to mode , which is an inclusive or of the bits R_OK, W_OK and X_OK. Specifying mode as F_OK (i.e. 0) tests whether the directories leading to the file can be searched and the file exists.

The real user ID and the group access list (including the real group ID) are used in verifying permission, so this call is useful to set-UID programs.

Notice that only access bits are checked. A directory may be indicated as writable by access , but an attempt to open it for writing will fail (although files may be created there); a file may look executable, but execve will fail unless it is in proper format.

If 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. Access to the file is denied if one or more of the following are true:

15 [ENOTDIR] A component of the path prefix is not a directory.

15 [ENOENT] The argument path name was too long.

15 [ENOENT] Read, write, or execute (search) permission is requested for a null path name or the named file does not exist.

15 [EPERM] The argument contains a byte with the high-order bit set.

15 [ELOOP] Too many symbolic links were encountered in translating the pathname.

15 [EROFS] Write access is requested for a file on a read-only file system.

15 [ETXTBSY] Write access is requested for a pure procedure (shared text) file that is being executed.

15 [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.

15 [EFAULT] Path points outside the process's allocated address space.

chmod(2), stat(2)