RCMD(3)             UNIX Programmer's Manual		  RCMD(3)



NAME
     rcmd, rresvport, ruserok - routines for returning a stream
     to a remote command

SYNOPSIS
     rem = rcmd(ahost, inport, locuser, remuser, cmd, fd2p);
     char **ahost;
     int inport;
     char *locuser, *remuser, *cmd;
     int *fd2p;

     s = rresvport(port);
     int *port;

     ruserok(rhost, superuser, ruser, luser);
     char *rhost;
     int superuser;
     char *ruser, *luser;

DESCRIPTION
     _R_c_m_d is a routine used by the super-user to execute a com-
     mand on a remote machine using an authentication scheme
     based on reserved port numbers.  _R_r_e_s_v_p_o_r_t is a routine
     which returns a descriptor to a socket with an address in
     the privileged port space.  _R_u_s_e_r_o_k is a routine used by
     servers to authenticate clients requesting service with
     _r_c_m_d.  All three functions are present in the same file and
     are used by the _r_s_h_d(8C) server (among others).

     _R_c_m_d looks up the host *_a_h_o_s_t using _g_e_t_h_o_s_t_b_y_n_a_m_e(3N),
     returning -1 if the host does not exist.  Otherwise *_a_h_o_s_t
     is set to the standard name of the host and a connection is
     established to a server residing at the well-known Internet
     port _i_n_p_o_r_t.

     If the connection succeeds, a socket in the Internet domain
     of type SOCK_STREAM is returned to the caller, and given to
     the remote command as stdin and stdout.  If _f_d_2_p is non-
     zero, then an auxiliary channel to a control process will be
     set up, and a descriptor for it will be placed in *_f_d_2_p.
     The control process will return diagnostic output from the
     command (unit 2) on this channel, and will also accept bytes
     on this channel as being UNIX signal numbers, to be for-
     warded to the process group of the command.  If _f_d_2_p is 0,
     then the stderr (unit 2 of the remote command) will be made
     the same as the stdout and no provision is made for sending
     arbitrary signals to the remote process, although you may be
     able to get its attention by using out-of-band data.

     The protocol is described in detail in _r_s_h_d(8C).





Printed 11/26/99	  May 14, 1986				1






RCMD(3)             UNIX Programmer's Manual		  RCMD(3)



     The _r_r_e_s_v_p_o_r_t routine is used to obtain a socket with a
     privileged address bound to it.  This socket is suitable for
     use by _r_c_m_d and several other routines.  Privileged Internet
     ports are those in the range 0 to 1023.  Only the super-user
     is allowed to bind an address of this sort to a socket.

     _R_u_s_e_r_o_k takes a remote host's name, as returned by a
     _g_e_t_h_o_s_t_b_y_a_d_d_r(3N) routine, two user names and a flag indi-
     cating whether the local user's name is that of the super-
     user.  It then checks the files /_e_t_c/_h_o_s_t_s._e_q_u_i_v and, possi-
     bly, ._r_h_o_s_t_s in the current working directory (normally the
     local user's home directory) to see if the request for ser-
     vice is allowed.  A 0 is returned if the machine name is
     listed in the ``hosts.equiv'' file, or the host and remote
     user name are found in the ``.rhosts'' file; otherwise
     _r_u_s_e_r_o_k returns -1.  If the _s_u_p_e_r_u_s_e_r flag is 1, the check-
     ing of the ``host.equiv'' file is bypassed.  If the local
     domain (as obtained from _g_e_t_h_o_s_t_n_a_m_e(2)) is the same as the
     remote domain, only the machine name need be specified.

SEE ALSO
     rlogin(1C), rsh(1C), intro(2), rexec(3), rexecd(8C),
     rlogind(8C), rshd(8C)

DIAGNOSTICS
     _R_c_m_d returns a valid socket descriptor on success.  It
     returns -1 on error and prints a diagnostic message on the
     standard error.

     _R_r_e_s_v_p_o_r_t returns a valid, bound socket descriptor on suc-
     cess.  It returns -1 on error with the global value _e_r_r_n_o
     set according to the reason for failure.  The error code
     EAGAIN is overloaded to mean ``All network ports in use.''






















Printed 11/26/99	  May 14, 1986				2