227 lines
6.3 KiB
Groff
227 lines
6.3 KiB
Groff
.\" Copyright (c) 1983, 1987 The Regents of the University of California.
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.\" All rights reserved.
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.\"
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.\" Redistribution and use in source and binary forms are permitted provided
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.\" that: (1) source distributions retain this entire copyright notice and
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.\" comment, and (2) distributions including binaries display the following
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.\" acknowledgement: ``This product includes software developed by the
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.\" University of California, Berkeley and its contributors'' in the
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.\" documentation or other materials provided with the distribution and in
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.\" all advertising materials mentioning features or use of this software.
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.\" Neither the name of the University nor the names of its contributors may
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.\" be used to endorse or promote products derived from this software without
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.\" specific prior written permission.
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.\" THIS SOFTWARE IS PROVIDED ``AS IS'' AND WITHOUT ANY EXPRESS OR IMPLIED
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.\" WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED WARRANTIES OF
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.\" MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE.
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.\"
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.\" @(#)gethostbyname.3 6.12 (Berkeley) 6/23/90
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.\"
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.TH GETHOSTBYNAME 3 "June 23, 1990"
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.UC 5
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.SH NAME
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gethostbyname, gethostbyaddr, gethostent, sethostent, endhostent, herror \- get network host entry
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.SH SYNOPSIS
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.B "#include <netdb.h>
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.PP
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.B "extern int h_errno;
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.PP
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.B "struct hostent *gethostbyname(name)
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.br
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.B "char *name;
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.PP
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.B "struct hostent *gethostbyname2(name, af)
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.br
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.B "char *name; int af;
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.PP
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.B "struct hostent *gethostbyaddr(addr, len, type)
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.br
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.B "char *addr; int len, type;
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.PP
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.B "struct hostent *gethostent()
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.PP
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.B "sethostent(stayopen)
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.br
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.B "int stayopen;
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.PP
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.B "endhostent()
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.PP
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.B "herror(string)
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.br
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.B "char *string;
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.PP
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.SH DESCRIPTION
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.IR Gethostbyname ,
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.IR gethostbyname2 ,
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and
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.I gethostbyaddr
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each return a pointer to an object with the
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following structure describing an internet host
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referenced by name or by address, respectively.
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This structure contains either the information obtained from the name server,
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.IR named (8),
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or broken-out fields from a line in
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.IR /etc/hosts .
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If the local name server is not running these routines do a lookup in
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.IR /etc/hosts .
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.RS
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.PP
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.nf
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struct hostent {
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char *h_name; /* official name of host */
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char **h_aliases; /* alias list */
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int h_addrtype; /* host address type */
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int h_length; /* length of address */
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char **h_addr_list; /* list of addresses from name server */
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};
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#define h_addr h_addr_list[0] /* address, for backward compatibility */
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.ft R
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.ad
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.fi
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.RE
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.PP
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The members of this structure are:
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.TP \w'h_addr_list'u+2n
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h_name
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Official name of the host.
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.TP \w'h_addr_list'u+2n
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h_aliases
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A zero terminated array of alternate names for the host.
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.TP \w'h_addr_list'u+2n
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h_addrtype
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The type of address being returned; usually AF_INET.
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.TP \w'h_addr_list'u+2n
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h_length
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The length, in bytes, of the address.
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.TP \w'h_addr_list'u+2n
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h_addr_list
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A zero terminated array of network addresses for the host.
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Host addresses are returned in network byte order.
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.TP \w'h_addr_list'u+2n
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h_addr
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The first address in h_addr_list; this is for backward compatibility.
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.PP
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When using the nameserver,
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.I gethostbyname
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will search for the named host in the current domain and its parents
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unless the name ends in a dot.
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If the name contains no dot, and if the environment variable ``HOSTALAIASES''
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contains the name of an alias file, the alias file will first be searched
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for an alias matching the input name.
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See
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.IR hostname (7)
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for the domain search procedure and the alias file format.
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.PP
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.I Gethostbyname2
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is an evolution of
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.I gethostbyname
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intended to allow lookups in address families other than AF_INET, for example
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AF_INET6. Currently the
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.I af
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argument must be specified as
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.I AF_INET
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else the function will return \s-2NULL\s+2 after having set
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.I h_errno
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to \s-2NETDB_INTERNAL\s+2.
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.PP
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.I Sethostent
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may be used to request the use of a connected TCP socket for queries.
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If the
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.I stayopen
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flag is non-zero,
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this sets the option to send all queries to the name server using TCP
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and to retain the connection after each call to
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.I gethostbyname
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or
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.IR gethostbyaddr .
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Otherwise, queries are performed using UDP datagrams.
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.PP
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.I Endhostent
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closes the TCP connection.
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.SH DIAGNOSTICS
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.PP
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Error return status from
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.I gethostbyname
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and
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.I gethostbyaddr
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is indicated by return of a null pointer.
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The external integer
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.IR h_errno
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may then be checked to see whether this is a temporary failure
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or an invalid or unknown host.
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The routine
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.I herror
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can be used to print an error message describing the failure.
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If its argument
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.I string
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is non-NULL, it is printed, followed by a colon and a space.
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The error message is printed with a trailing newline.
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.PP
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.IR h_errno
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can have the following values:
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.RS
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.IP NETDB_INTERNAL \w'HOST_NOT_FOUND'u+2n
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This indicates an internal error in the library, unrelated to the network
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or name service.
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.I errno
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will be valid in this case; see
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.IR perror (3).
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.IP HOST_NOT_FOUND \w'HOST_NOT_FOUND'u+2n
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No such host is known.
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.IP TRY_AGAIN \w'HOST_NOT_FOUND'u+2n
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This is usually a temporary error
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and means that the local server did not receive
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a response from an authoritative server.
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A retry at some later time may succeed.
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.IP NO_RECOVERY \w'HOST_NOT_FOUND'u+2n
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Some unexpected server failure was encountered.
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This is a non-recoverable error.
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.IP NO_DATA \w'HOST_NOT_FOUND'u+2n
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The requested name is valid but does not have an IP address;
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this is not a temporary error.
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This means that the name is known to the name server but there is no address
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associated with this name.
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Another type of request to the name server using this domain name
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will result in an answer;
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for example, a mail-forwarder may be registered for this domain.
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.RE
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.SH FILES
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/etc/hosts
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.SH "SEE ALSO"
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resolver(3), hosts(5), hostname(7), named(8)
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.SH CAVEAT
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.PP
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.I Gethostent
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is defined, and
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.I sethostent
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and
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.I endhostent
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are redefined,
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when
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.IR libc
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is built to use only the routines to lookup in
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.IR /etc/hosts
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and not the name server.
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.PP
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.I Gethostent
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reads the next line of
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.IR /etc/hosts ,
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opening the file if necessary.
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.PP
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.I Sethostent
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is redefined to open and rewind the file. If the
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.I stayopen
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argument is non-zero,
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the hosts data base will not be closed after each call to
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.I gethostbyname
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or
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.IR gethostbyaddr .
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.I Endhostent
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is redefined to close the file.
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.SH BUGS
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All information
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is contained in a static area
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so it must be copied if it is
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to be saved. Only the Internet
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address format is currently understood.
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