RCMD(3)

NAME
rcmd, rresvport, ruserok - routines for returning a stream to a remote command

SYNOPSIS

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 *ruser, *luser;

DESCRIPTION
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 (among others).

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 a socket.

Ruserok takes a remote host's name, as returned by the gethostbyaddr(3) routine, two user names and a flag indicating whether the local user's name is that of the super-user. Then, if the user is NOT the super-user, it checks the files /etc/hosts.equiv. If that lookup is not done, or is unsuccessful, the .rhosts in the local user's home directory is checked to see if the request for service is allowed. If this file is owned by anyone other than the user or the super-user, or if it is writeable by anyone other than the owner, the check automatically fails. 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 local domain (as obtained from gethostname(2)) is the same as the remote domain, only the machine name need be specified.

SEE ALSO
rlogin(1), rsh(1), intro(2), rexec(3), rexecd(8), rlogind(8), rshd(8)

DIAGNOSTICS
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.''