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ACCESS(2)		    BSD	System Calls Manual		     ACCESS(2)

     access, eaccess, faccessat	-- check accessibility of a file

     Standard C	Library	(libc, -lc)

     #include <unistd.h>

     access(const char *path, int mode);

     eaccess(const char	*path, int mode);

     faccessat(int fd, const char *path, int mode, int flag);

     The access() and eaccess()	system calls check the accessibility of	the
     file named	by the path argument for the access permissions	indicated by
     the mode argument.	 The value of mode is either the bitwise-inclusive OR
     of	the access permissions to be checked (R_OK for read permission,	W_OK
     for write permission, and X_OK for	execute/search permission), or the ex-
     istence test (F_OK).

     For additional information, see the File Access Permission	section	of

     The eaccess() system call uses the	effective user ID and the group	access
     list to authorize the request; the	access() system	call uses the real
     user ID in	place of the effective user ID,	the real group ID in place of
     the effective group ID, and the rest of the group access list.

     The faccessat() system call is equivalent to access() except in the case
     where path	specifies a relative path.  In this case the file whose	acces-
     sibility is to be determined is located relative to the directory associ-
     ated with the file	descriptor fd instead of the current working direc-
     tory.  If faccessat() is passed the special value AT_FDCWD	in the fd pa-
     rameter, the current working directory is used and	the behavior is	iden-
     tical to a	call to	access().  Values for flag are constructed by a	bit-
     wise-inclusive OR of flags	from the following list, defined in <fcntl.h>:

	     The checks	for accessibility are performed	using the effective
	     user and group IDs	instead	of the real user and group ID as re-
	     quired in a call to access().

     Even if a process's real or effective user	has appropriate	privileges and
     indicates success for X_OK, the file may not actually have	execute	per-
     mission bits set.	Likewise for R_OK and W_OK.

     Upon successful completion, the value 0 is	returned; otherwise the
     value -1 is returned and the global variable errno	is set to indicate the

     Access to the file	is denied if:

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

     [ENAMETOOLONG]	A component of a pathname exceeded 255 characters, or
			an entire path name exceeded 1023 characters.

     [ENOENT]		The named file does not	exist.

     [ELOOP]		Too many symbolic links	were encountered in translat-
			ing the	pathname.

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

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

     [EACCES]		Permission bits	of the file mode do not	permit the re-
			quested	access,	or search permission is	denied on a
			component of the path prefix.

     [EFAULT]		The path argument points outside the process's allo-
			cated address space.

     [EIO]		An I/O error occurred while reading from or writing to
			the file system.

     Also, the faccessat() system call may fail	if:

     [EBADF]		The path argument does not specify an absolute path
			and the	fd argument is neither AT_FDCWD	nor a valid
			file descriptor.

     [EINVAL]		The value of the flag argument is not valid.

     [ENOTDIR]		The path argument is not an absolute path and fd is
			neither	AT_FDCWD nor a file descriptor associated with
			a directory.

     chmod(2), intro(2), stat(2)

     The access() system call is expected to conform to	ISO/IEC	9945-1:1990
     ("POSIX.1").  The faccessat() system call follows The Open	Group Extended
     API Set 2 specification.

     The access() function appeared in Version 7 AT&T UNIX.  The faccessat()
     system call appeared in FreeBSD 8.0.

     The access() system call is a potential security hole due to race condi-
     tions and should never be used.  Set-user-ID and set-group-ID applica-
     tions should restore the effective	user or	group ID, and perform actions
     directly rather than use access() to simulate access checks for the real
     user or group ID.	The eaccess() system call likewise may be subject to
     races if used inappropriately.

     access() remains useful for providing clues to users as to	whether	opera-
     tions make	sense for particular filesystem	objects	(e.g. 'delete' menu
     item only highlighted in a	writable folder	... avoiding interpretation of
     the st_mode bits that the application might not understand	-- e.g.	in the
     case of AFS).  It also allows a cheaper file existence test than stat(2).

BSD				April 10, 2008				   BSD


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