RCMD(3N)                                                              RCMD(3N)


NAME
     rcmd, rresvport, ruserok, iruserok, rcmd_af, rresvport_af, iruserok_sa -
     routines for returning a stream to a remote command

SYNOPSIS
     rcmd(char **ahost, u_short inport, char *locuser, char *remuser,
               char *cmd, int *fd2p);

     rresvport(int *port);

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

     iruserok(unsigned long raddr, int superuser, const char *ruser,
                    const char *luser);

     rcmd_af(char **ahost, u_short inport, char *locuser, char *remuser,
                    const char*cmd, int *fd2p, int af);

     rresvport_af(int *fd2p, int af);

     iruserok_sa(const void *ra, socklen_t rlen, int superuser,
                    const char *ruser, const char *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(1M)
     server (among others).

     Rcmd looks up the host *ahost using getaddrinfo(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(1M).


     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 512 to
     1023.  Only the super-user is allowed to bind an address of this sort to
     a socket.

     The iruserok and ruserok functions take a remote host's IP address or
     name, as returned by one of the name resolution routines, 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 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 ``hosts.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.

     The functions with an _af or _sa suffix, i.e., rcmd_af, rresvport_af and
     iruserok_sa, work the same as the corresponding functions without a
     suffix, except that they are capable of handling both IPv6 and IPv4
     ports.  The _af suffix means that the function has an additional af
     argument which is used to specify the address family, (see below).  The
     af argument extension is implemented for functions that have no binary
     address argument.  Instead, the af argument specifies which address
     family is desired.  The _sa suffix means that the function has general
     socket address and length arguments.  As the socket address is a protocol
     independent data structure, IPv4 and IPv6 socket address can be passed as
     desired.  The sa argument extension is implemented for functions that
     pass a protocol dependent binary address argument.  The argument needs to
     be replaced with a more general address structure to support multiple
     address families in a general way.

     The functions with neither an _af suffix nor an _sa suffix work for IPv4
     only, except for ruserok which can handle both IPv6 and IPv4.  To switch
     the address family, the af argument must be filled with AF_INET, or
     AF_INET6.  For rcmd_af, AF_UNSPEC is also allowed.

SEE ALSO
     rlogin(1C), rsh(1C), intro(2), rexec(3N), rexecd(1M), rlogind(1M),
     rshd(1M).

     Advanced Socket API for IPv6: draft-ietf-ipngwg-rfc2292bis-07.txt

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.''


                                                                        Page 2