Name

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

Syntax

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

The rcmd subroutine is used by the superuser to execute a command on a remote machine using an authentication scheme based on reserved port numbers.  The rresvport subroutine is a routine that returns a descriptor to a socket with an address in the privileged port space. The ruserok subroutine 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() server (among others).

The rcmd subroutine looks up the host *ahost using gethostbyname(,), returning −1 if the host does not exist. For further information, see gethostent(.). 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 nonzero, 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(.).

The rresvport subroutine 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 superuser is allowed to bind an address of this sort to a socket.

The ruserok subroutine takes a remote host’s name, as returned by a gethostent() routine, two user names and a flag indicating if the local user’s name is the superuser.  It then checks the files /etc/hosts.equiv and .rhosts in the 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.

See Also

rlogin(1c), rsh(1c), gethostent(3n), rexec(3x), rexecd(8c), rlogind(8c), rshd(8c)