rcmd, rresvport, ruserok - routines for returning a stream to a remote
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
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(8) server
Rcmd looks up the host *ahost using gethostbyname(3), 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(8).
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
Ruserok takes a remote host's name, as returned by a 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
/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(3)) is the same as the remote
domain, only the machine name need be specified.
rlogin(1), rsh(1), intro(2), rexec(3), rexecd(8), rlogind(8), rshd(8)
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.''