.\" Copyright (c) 1983 The Regents of the University of California.
.\" All rights reserved.
.\"
.\" Redistribution and use in source and binary forms are permitted provided
.\" that: (1) source distributions retain this entire copyright notice and
.\" comment, and (2) distributions including binaries display the following
.\" acknowledgement:  ``This product includes software developed by the
.\" University of California, Berkeley and its contributors'' in the
.\" documentation or other materials provided with the distribution and in
.\" all advertising materials mentioning features or use of this software.
.\" Neither the name of the University nor the names of its contributors may
.\" be used to endorse or promote products derived from this software without
.\" specific prior written permission.
.\" THIS SOFTWARE IS PROVIDED ``AS IS'' AND WITHOUT ANY EXPRESS OR IMPLIED
.\" WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED WARRANTIES OF
.\" MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE.
.\"
.\"	@(#)rcmd.3	6.10 (Berkeley) 6/23/90
.\"
.TH RCMD 3 "June 23, 1990"
.UC 5
.SH NAME
rcmd, rresvport, ruserok \- routines for returning a stream to a remote command
.SH SYNOPSIS
.nf
.PP
.B "rem = rcmd(ahost, inport, locuser, remuser, cmd, fd2p);"
.B char **ahost;
.B int inport;
.B "char *locuser, *remuser, *cmd;"
.B int *fd2p;
.PP
.B s = rresvport(port);
.B int *port;
.PP
.B "ruserok(rhost, superuser, ruser, luser);"
.B char *rhost;
.B int superuser;
.B char *ruser, *luser;
.fi
.SH DESCRIPTION
.I Rcmd
is a routine used by the super-user to execute a command on
a remote machine using an authentication scheme based
on reserved port numbers.
.I Rresvport
is a routine which returns a descriptor to a socket
with an address in the privileged port space.
.I Ruserok
is a routine used by servers
to authenticate clients requesting service with
.IR rcmd .
All three functions are present in the same file and are used
by the
.IR rshd (8)
server (among others).
.PP
.I Rcmd
looks up the host
.I *ahost
using
.IR gethostbyname (3),
returning \-1 if the host does not exist.
Otherwise
.I *ahost
is set to the standard name of the host
and a connection is established to a server
residing at the well-known Internet port
.IR inport .
.PP
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 
.B stdin
and
.BR stdout .
If
.I fd2p
is non-zero, then an auxiliary channel to a control
process will be set up, and a descriptor for it will be placed
in
.IR *fd2p .
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
.I fd2p
is 0, then the 
.B stderr
(unit 2 of the remote
command) will be made the same as the 
.B 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.
.PP
The protocol is described in detail in
.IR rshd (8).
.PP
The
.I rresvport
routine is used to obtain a socket with a privileged
address bound to it.  This socket is suitable for use
by 
.I rcmd
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.
.PP
.I Ruserok
takes a remote host's name, as returned by the
.IR 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
.B NOT
the super-user, it checks the files
.IR /etc/hosts.equiv .
If that lookup is not done, or is unsuccessful, the
.I .rhosts
in the local user's home directory 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 ``hosts.equiv'' file, or the host and remote
user name are found in the ``.rhosts'' file; otherwise
.I ruserok
returns \-1.
If the local domain (as obtained from \fIgethostname\fP\|(2))
is the same as the remote domain, only the machine name need be specified.
.SH SEE ALSO
rlogin(1), rsh(1), intro(2), rexec(3), rexecd(8), rlogind(8), rshd(8)
.SH DIAGNOSTICS
.I Rcmd
returns a valid socket descriptor on success.
It returns -1 on error and prints a diagnostic message on the standard error.
.PP
.I Rresvport
returns a valid, bound socket descriptor on success.
It returns -1 on error with the global value
.I errno
set according to the reason for failure.
The error code EAGAIN is overloaded to mean ``All network ports in use.''