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 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().

     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 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(), eaccess(), 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 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 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.

     [EINTEGRITY]       Corrupted data was detected while reading from 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 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.

SECURITY CONSIDERATIONS

     The access() system call is a potential security hole due to race conditions and should
     never be used.  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.  The eaccess() system call likewise may be subject to races
     if used inappropriately.

     access() remains useful for providing clues to users as to whether operations 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).