.TH RCMD 3X "17 March 1982"
.UC 4
.SH NAME
rcmd, rresvport, ruserok \- routines for returning a stream to a remote command
.SH SYNOPSIS
.nf
.B rem = rcmd(ahost, inport, locuser, remuser, cmd, fd2p);
.B char **ahost;
.B u_short 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 (8C)
server (among others).
.PP
.I Rcmd
looks up the host
.I *ahost
using
.IR gethostbyname (3N),
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 call succeeds, a socket 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 (8C).
.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 sevral other routines.  Privileged addresses consist
of a port 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 gethostent (3N)
routine, two user names and a flag indicating if
the local user's name is 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 1 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 0.  If the
.I superuser
flag is 1, the checking of the ``host.equiv'' file is
bypassed.
.SH SEE ALSO
rlogin(1C),
rsh(1C),
rexec(3X),
rexecd(8C),
rlogind(8C),
rshd(8C)
.SH BUGS
There is no way to specify options to the
.I socket
call
which
.I rcmd
makes.