cc [ flag ... ] file ... -lsocket -lnsl [ library ... ]
int rcmd(char **ahost,
unsigned short inport,
const char *luser,
const char *ruser,
const char *cmd, int *fd2p);
int rresvport(int *port);
int ruserok(const char *rhost, int suser, const char *ruser, const char *luser);
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 in.rshd.1m 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 its standard input (file descriptor 0) and standard output (file descriptor 1). 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 (file descriptor 2) on this channel, and will also accept bytes on this channel as signal numbers, to be forwarded to the process group of the command. If fd2p is 0, then the standard error (file descriptor 2) of the remote command will be made the same as its standard output 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 in.rshd.1m
The rresvport() routine is used to obtain a socket bound to a privileged port number. This socket is suitable for use by rcmd() and several other routines. Privileged Internet ports are those in the range 1 to 1023. Only the super-user is allowed to bind a socket to a privileged port number. The application must pass in port, which must be in the range 512 to 1023. The system first tries to bind to that port number. If it fails, it then tries to bind to port numbers less than port until either it succeeds or port number 512 is reached.
ruserok() takes a remote host's name, as returned by a gethostbyaddr() (see gethostbyname.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 local user's home directory to see if the request for service is allowed. 0 is returned if the machine name is listed in the /etc/hosts.equiv file, or the host and remote user name are found in the .rhosts file; otherwise ruserok() returns -1. If the super-user flag is 1, the checking of the /etc/hosts.equiv file is bypassed.
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.
These interfaces are unsafe in multithreaded applications. Unsafe interfaces should be called only from the main thread.
Created by unroff & hp-tools. © by Hans-Peter Bischof. All Rights Reserved (1997).
Last modified 21/April/97