.\" Copyright (c) 1983 Regents of the University of California.
.\" All rights reserved.  The Berkeley software License Agreement
.\" specifies the terms and conditions for redistribution.
.\"
.\"	@(#)rcmd.3	6.7 (Berkeley) 5/14/86
.\"
.TH RCMD 3 "May 14, 1986"
.UC 5
.SH NAME
rcmd, rresvport, ruserok \- routines for returning a stream to a remote command
.SH SYNOPSIS
.nf
.B "#include <sys/types.h>"
.B "#include <net/netlib.h>"
.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 a
.IR gethostbyaddr (3)
routine, two user names and a flag indicating whether
the local user's name is that of the super-user.  It then
checks the files 
.I /etc/hosts.equiv
and, possibly, 
.I .rhosts
in the current working directory (normally the local
user's home directory) to see if the request for
service 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 
.I ruserok
returns \-1.  If the
.I superuser
flag is 1, the checking of the ``host.equiv'' file is
bypassed.
If the local domain (as obtained from \fIgethostname\fP\|(3))
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.''