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

NNAAMMEE
     rrccmmdd, rrrreessvvppoorrtt, rruusseerrookk - routines for returning a stream to a remote
     command

SSYYNNOOPPSSIISS
     ##iinncclluuddee <<uunniissttdd..hh>>

     _i_n_t
     rrccmmdd(_c_h_a_r _*_*_a_h_o_s_t, _i_n_t _i_n_p_o_r_t, _c_o_n_s_t _c_h_a_r _*_l_o_c_u_s_e_r, _c_o_n_s_t _c_h_a_r _*_r_e_m_u_s_e_r,
             _c_o_n_s_t _c_h_a_r _*_c_m_d, _i_n_t _*_f_d_2_p)

     _i_n_t
     rrrreessvvppoorrtt(_i_n_t _*_p_o_r_t)

     _i_n_t
     rruusseerrookk(_c_o_n_s_t _c_h_a_r _*_r_h_o_s_t, _i_n_t _s_u_p_e_r_u_s_e_r, _c_o_n_s_t _c_h_a_r _*_r_u_s_e_r,
             _c_o_n_s_t _c_h_a_r _*_l_u_s_e_r)

DDEESSCCRRIIPPTTIIOONN
     The rrccmmdd() function is used by the super-user to execute a command on a
     remote machine using an authentication scheme based on reserved port num-
     bers.  The rrrreessvvppoorrtt() function returns a descriptor to a socket with an
     address in the privileged port space.  The rruusseerrookk() function is used by
     servers to authenticate clients requesting service with rrccmmdd().  All
     three functions are present in the same file and are used by the rshd(8)
     server (among others).

     The rrccmmdd() function looks up the host _*_a_h_o_s_t using gethostbyname(3),  re-
     turning -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 re-
     siding 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
     _s_t_d_i_n and _s_t_d_o_u_t. 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 forwarded to the process group of the
     command.  If _f_d_2_p is 0, then the _s_t_d_e_r_r (unit 2 of the remote command)
     will be made the same as the _s_t_d_o_u_t 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 rshd(8).

     The rrrreessvvppoorrtt() function is used to obtain a socket with a privileged ad-
     dress bound to it.  This socket is suitable for use by rrccmmdd() and several
     other functions.  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.

     The rruusseerrookk() argument takes a remote host's name, as returned by the
     gethostbyaddr(3) routine, two user names and a flag indicating whether
     the local user's name is that of the super-user.  Then, if the user is
     _N_O_T the super-user, it checks the files _/_e_t_c_/_h_o_s_t_s_._e_q_u_i_v. If that lookup
     is not done, or is unsuccessful, the _._r_h_o_s_t_s in the local user's home di-
     rectory is checked to see if the request for service is allowed.  If this
     file is owned by anyone other than the user or the super-user, or if it
     is writeable by anyone other than the owner, the check automatically
     fails.  A 0 is returned if the machine name is listed in the
     ``_h_o_s_t_s_._e_q_u_i_v'' file, or the host and remote user name are found in the
     ``_._r_h_o_s_t_s'' file; otherwise rruusseerrookk() returns -1.  If the local domain
     (as obtained from gethostname(2))  is the same as the remote domain, only
     the machine name need be specified.

DDIIAAGGNNOOSSTTIICCSS
     The rrccmmdd() function returns a valid socket descriptor on success.  It re-
     turns -1 on error and prints a diagnostic message on the standard error.

     The rrrreessvvppoorrtt() function 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.''

SSEEEE AALLSSOO
     rlogin(1),  rsh(1),  intro(2),  rexec(3),  rexecd(8),  rlogind(8),
     rshd(8)

HHIISSTTOORRYY
     These functions appeared in 4.2BSD.

4.2 Berkeley Distribution       April 19, 1991                               2














































