rcmd, rresvport, ruserok - routines for returning a stream to a remote command
rem = rcmd(ahost, inport, locuser, remuser, cmd, fd2p);
char *locuser, *remuser, *cmd;
s = rresvport(port);
ruserok(rhost, superuser, ruser, luser);
char *ruser, *luser;
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. Rresvport is a routine which
returns a descriptor to a socket with an address in the privileged port space. Ruserok is
a routine used by servers to authenticate clients requesting service with rcmd. All three
functions are present in the same file and are used by the rshd(8C) server (among others).
Rcmd looks up the host *ahost using gethostbyname(3N), returning -1 if the host does not
exist. Otherwise *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 inport.
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 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 *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 fd2p 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 rshd(8C).
The rresvport routine is used to obtain a socket with a privileged address bound to it.
This socket is suitable for use by 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.
Ruserok takes a remote host's name, as returned by a gethostbyaddr(3N) 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 /etc/hosts.equiv and, possibly, .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 ruserok returns
-1. If the superuser flag is 1, the checking of the ``host.equiv'' file is bypassed. If
the local domain (as obtained from gethostname(2)) is the same as the remote domain, only
the machine name need be specified.
rlogin(1C), rsh(1C), intro(2), rexec(3), rexecd(8C), rlogind(8C), rshd(8C)
Rcmd returns a valid socket descriptor on success. It returns -1 on error and prints a
diagnostic message on the standard error.
Rresvport returns a valid, bound socket descriptor on success. It returns -1 on error
with the global value errno set according to the reason for failure. The error code
EAGAIN is overloaded to mean ``All network ports in use.''
4.2 Berkeley Distribution May 14, 1986 RCMD(3)