RCMD(3)                   386BSD Programmer's Manual                   RCMD(3)

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

SYNOPSIS
     #include <unistd.h>

     int
     rcmd(char **ahost, int inport, const char *locuser, const char *remuser,
             const char *cmd, int *fd2p)

     int
     rresvport(int *port)

     int
     ruserok(const char *rhost, int superuser, const char *ruser,
             const char *luser)

DESCRIPTION
     The rcmd() function is used by the super-user to execute a command on a
     remote machine using an authentication scheme based on reserved port
     numbers.  The rresvport() function returns a descriptor to a socket with
     an address in the privileged port space.  The ruserok() function is 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).

     The rcmd() function 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() function is used to obtain a socket with a privileged
     address bound to it.  This socket is suitable for use by rcmd() and
     several other functions.  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.

     The ruserok() argument 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.

DIAGNOSTICS
     The rcmd() function returns a valid socket descriptor on success.  It
     returns -1 on error and prints a diagnostic message on the standard
     error.

     The rresvport() function 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.''

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

HISTORY
     These functions appeared in 4.2BSD.

4.2 Berkeley Distribution       April 19, 1991                               2