ACCESS(2)                     System Calls Manual                    ACCESS(2)

NAME
     access, faccessat – check accessibility of a file

SYNOPSIS
     #include <unistd.h>

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

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

DESCRIPTION
     The access() system call checks 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 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
     accessibility is to be determined is located relative to the directory
     associated with the file descriptor fd instead of the current working
     directory.  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().

     AT_SYMLINK_NOFOLLOW
             If path names a symbolic link, the status of the symbolic link is
             returned.

     AT_SYMLINK_NOFOLLOW_ANY
             If path names a symbolic link, the status of the symbolic link is
             returned and if the path has any other symbolic links, an error
             is returned.

     Even if a process has appropriate privileges and indicates success for
     X_OK, the file may not actually have execute permission 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() or faccessat() will fail if:

     [EINVAL]           The value of the mode argument is invalid.

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

     [ENAMETOOLONG]     A component of a pathname exceeded {NAME_MAX}
                        characters, or an entire path name exceeded {PATH_MAX}
                        characters.

     [ENOENT]           The named file does not exist.

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

     [ELOOP]            AT_SYMLINK_NOFOLLOW_ANY was passed and a symbolic link
                        was encountered in translating 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
                        allocated 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.

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

STANDARDS
     The access() system call is expected to conform to IEEE Std 1003.1-1990
     (“POSIX.1”).  The faccessat() system call is expected to conform to
     POSIX.1-2008 .

HISTORY
     The access() function appeared in Version 7 AT&T UNIX.

SECURITY CONSIDERATIONS
     The result of access() should not be used to make an actual access
     control decision, since its response, even if correct at the moment it is
     formed, may be outdated at the time you act on it.  access() results
     should only be used to pre-flight, such as when configuring user
     interface elements or for optimization purposes.  The actual access
     control decision should be made by attempting to execute the relevant
     system call while holding the applicable credentials, and properly
     handling any resulting errors; and this must be done even though access()
     may have predicted success.

     Additionally, set-user-ID and set-group-ID applications 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.

macOS 15.2                    September 15, 2014                    macOS 15.2