returning -1 if the host does not exist. Otherwise is set to the standard name of the host and a connection is established to a server residing at the well-known Internet port If the connection succeeds, a socket in the Internet domain of type is returned to the caller, and given to the remote command as and If is non- zero, then an auxiliary channel to a control process will be set up, and a descriptor for it will be placed in 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 sig- nal numbers, to be forwarded to the process group of the command. If is 0, then the (unit 2 of the remote command) will be made the same as the and no provision is made for sending arbitrary sig- nals 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 The function is used to obtain a socket with a privileged address bound to it. This socket is suitable for use by and several other functions. 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. The and functions take a remote host's IP address or name, respectively, two user names and a flag indicating whether the local user's name is that of the super-user. Then, if the user is the super-user, it checks the file. If that lookup is not done, or is unsuccessful, the in the local user's home directory is checked to see if the request for service is allowed. If this file does not exist, is not a regular file, is owned by anyone other than the user or the super-user, or is writeable by anyone other than the owner, the check automatically fails. Zero is returned if the machine name is listed in the file, or the host and remote user name are found in the file; otherwise and return -1. If the local domain (as obtained from is the same as the remote domain, only the machine name need be specified. If the IP address of the remote host is known, should be used in preference to as it does not require trusting the DNS server for the remote host's domain. The func- tion returns a valid socket descriptor on success. It returns -1 on error and prints a diagnostic message on the standard error. The function returns a valid, bound socket descriptor on success. It returns -1 on error with the global value set according to the reason for failure. The error code is overloaded to mean ``All network ports in use.'' These functions appeared in