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

NAME
     access, eaccess, faccessat — check accessibility of a file

LIBRARY
     Standard C Library (libc, -lc)

SYNOPSIS
     #include <unistd.h>

     int
     access(const char *path, int mode);

     int
     eaccess(const char *path, int mode);

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

DESCRIPTION
     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
     existence test (F_OK).

     For additional information, see the File Access Permission section of
     intro(2).

     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
     parameter, the current working directory is used and the behavior is
     identical to a call to access().  Values for flag are constructed by a
     bitwise-inclusive OR of flags from the following list, defined in
     <fcntl.h>:

     AT_EACCESS
	     The checks for accessibility are performed using the effective
	     user and group IDs instead of the real user and group ID as
	     required 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.

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

ERRORS
     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
			requested 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.

SECURITY CONSIDERATIONS
     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).

SEE ALSO
     chmod(2), intro(2), stat(2)

STANDARDS
     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.

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

BSD				April 10, 2008				   BSD
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