rcmd, rresvport, ruserok - routines for returning a stream to a remote
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 call succeeds, a socket 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 sig-
nal 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
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.
Ruserok takes a remote host's name, as returned by a 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 /etc/hosts.equiv and, pos-
sibly, .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 ruserok returns 0. If the superuser flag is 1, the
checking of the ``host.equiv'' file is bypassed.
rlogin(1C), rsh(1C), rexec(3X), rexecd(8C), rlogind(8C), rshd(8C)
There is no way to specify options to the socket call which rcmd makes.
4th Berkeley Distribution 17 March 1982 RCMD(3X)