rcmd(SLIB)                     6 January 1993                     rcmd(SLIB)


 Name

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

 Syntax


    rcmd (ahost, inport, locuser, remuser, cmd, fd2p)
    char **ahost;
    unsigned short inport;
    char *locuser, *remuser, *cmd;
    int *fd2p;

    int *port;

    ruserok (rhost, superuser, ruser, luser)
    char *rhost;
    intsuperuser;
    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 various servers,
    including rshd(ADMN) server (among others).

    rcmd looks up the host *ahost using gethostbyname(SLIB), 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 SOCKSTREAM is returned to the
    caller and given to the remote command as stdin and stdout.  If fd2p is
    non-zero, 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 signal numbers, to be
    forwarded to the process group of the command.  If fd2p is 0, the stderr
    (unit 2 of the remote command) will be made the same as the stdout. 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(ADMN).

    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 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 gethostbyname(SLIB)
    routine, two user names and a flag indicating if the local user's name is
    the super-user.  Then, if the user is not the super-user, it checks
    /etc/hosts.equiv.  If that lookup is not done, or is unsuccesful, 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 return value of zero is
    returned if the machine name is listed in the hosts.equiv file or if the
    host and remote user name are found in the .rhosts file; otherwise
    ruserok returns -1.

 Notes

    There is no way to specify options to the socket call which rcmd makes.

 See also

    hosts.equiv(SFF), rcmd(TC), rexec(SLIB), rexecd(ADMN), rhosts(SFF), rlog-
    in(TC), rlogind(ADMN) and rshd(ADMN).