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Sockets Library Functionsrcmd(3SOCKET)


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


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 rcmd_af(char **ahost, unsigned short inport, const char *luser, const char *ruser, const char *cmd, int *fd2p, int af);
 int rresvport(int *port);
 int rresvport_af(int *port, int af);
 int ruserok(const char *rhost, int suser, const char *ruser, const char *luser);



rcmd() is a routine used by the superuser to execute a command on a remote machine using an authentication scheme based on reserved port numbers. It is assumed that an AF_INET socket is returned with rcmd(). rcmd_af() allows the application to choose which type of socket is returned by passing in the address family, either AF_INET or AF_INET6.

rresvport() is a routine that returns a descriptor to a socket with an address in the privileged port space. rresvport_af() is equivalent to rresvport(), except that you can choose the type of socket address family that will be returned by rresvport_af(), either AF_INET or AF_INET6.

ruserok() is a routine used by servers to authenticate clients requesting service with rcmd.

All of these functions are present in the same file and are used by the in.rshd(1M) server (among others).

rcmd() and rcmd_af() look up the host *ahost using getipnodebyname(3SOCKET), 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() and rresvport_af() routines are used to obtain a socket bound to a privileged port number. This socket is suitable for use by rcmd() and rresvport_af() and several other routines. Privileged Internet ports are those in the range 1 to 1023. Only the superuser 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, the system then tries to bind to another unused privileged port, if one is available.

ruserok() takes a remote host's name, as returned by a gethostbyaddr() routine, two user names and a flag indicating whether the local user's name is that of the superuser. See gethostbyname(3NSL). 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 superuser flag is 1, the checking of the /etc/hosts.equiv file is bypassed.



rcmd() and rcmd_af() return a valid socket descriptor upon success. They returns -1 upon error and print a diagnostic message to standard error.

rresvport() and rresvport_af() return a valid, bound socket descriptor upon success. They return -1 upon error with the global value errno set according to the reason for failure.


system trusted hosts and users
user's trusted hosts and users



See attributes(5) for descriptions of the following attributes:




rlogin(1), rsh(1), in.rexecd(1M), in.rshd(1M), intro(2), gethostbyname(3NSL), getipnodebyname(3SOCKET), rexec(3SOCKET), attributes(5)



The error code EAGAIN is overloaded to mean "All network ports in use."

These interfaces are unsafe in multithreaded applications. Unsafe interfaces should be called only from the main thread.

SunOS 5.9Go To TopLast Changed 10 Nov 1999

Copyright 2002 Sun Microsystems, Inc. All rights reserved. Use is subject to license terms.