4.3BSD - /usr/man/cat3/rresvport.0

RCMD(3)                                                                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(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  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 provi‐
       sion 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 sev‐
       eral 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 a  gethostbyaddr(3N)
       routine,  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 current working direc‐
       tory (normally 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  ‘‘host.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.

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

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.’’


4.2 Berkeley Distribution        May 14, 1986                          RCMD(3)