NAME

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

USAGE

rem = rcmd(ahost, inport, locuser, remuser, cmd, fd2p); char **ahost; u_short 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 used by the super-user to execute a command on a remote machine using a dubious authentication scheme based on reserved port numbers.  Rresvport returns a descriptor to a socket with an address in the privileged port space.  Ruserok 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). 

Rcmd looks up the host *ahost using gethostbyname(3N).  It returns -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 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, which it forwards to the process group of the command.  If fd2p is zero, then the stderr (unit 2 of the remote command) will be made the same as the stdout and no provision will be 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 addresses consist of a port in the range zero 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 gethostent(3N) routine, two usernames and a flag indicating if the local username is the super-user.  It then checks the files /etc/hosts.equiv and, possibly, .rhosts in the current working directory (normally the local user’s home directory) to see if the request for service is allowed.  A 1 is returned if the machine name is listed in hosts.equiv, or the host and remote username are found in the .rhosts; otherwise ruserok returns zero.  If the superuser flag is 1, the check of host.equiv is bypassed. 

NOTES

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

RELATED INFORMATION

rlogin(1), rsh(1), rexec(3X), rexecd(8), rlogind(8), rshd(8)