4.3BSD-UWisc/man/cat3/rcmd.3
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 12/27/86 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 12/27/86 May 14, 1986 2