1.\" Copyright (c) 1983, 1987, 1991 The Regents of the University of California. 2.\" All rights reserved. 3.\" 4.\" Redistribution and use in source and binary forms, with or without 5.\" modification, are permitted provided that the following conditions 6.\" are met: 7.\" 1. Redistributions of source code must retain the above copyright 8.\" notice, this list of conditions and the following disclaimer. 9.\" 2. Redistributions in binary form must reproduce the above copyright 10.\" notice, this list of conditions and the following disclaimer in the 11.\" documentation and/or other materials provided with the distribution. 12.\" 3. All advertising materials mentioning features or use of this software 13.\" must display the following acknowledgement: 14.\" This product includes software developed by the University of 15.\" California, Berkeley and its contributors. 16.\" 4. Neither the name of the University nor the names of its contributors 17.\" may be used to endorse or promote products derived from this software 18.\" without specific prior written permission. 19.\" 20.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 21.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 22.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 23.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 24.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 25.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 26.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 27.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 28.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 29.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 30.\" SUCH DAMAGE. 31.\" 32.\" from: @(#)gethostbyname.3 6.14 (Berkeley) 7/31/91 33.\" $Id: gethostbyname.3,v 1.5 1994/04/07 07:00:10 deraadt Exp $ 34.\" 35.Dd July 31, 1991 36.Dt GETHOSTBYNAME 3 37.Os BSD 4.2 38.Sh NAME 39.Nm gethostbyname , 40.Nm gethostbyaddr , 41.Nm gethostent , 42.Nm sethostent , 43.Nm endhostent , 44.Nm herror 45.Nd get network host entry 46.Sh SYNOPSIS 47.Fd #include <netdb.h> 48.Fd extern int h_errno; 49.Ft struct hostent * 50.Fn gethostbyname "const char *name" 51.Ft struct hostent * 52.Fn gethostbyaddr "const char *addr" "int len" "int type" 53.Ft struct hostent * 54.Fn gethostent void 55.Fn sethostent "int stayopen" 56.Fn endhostent void 57.Fn herror "char *string" 58.Sh DESCRIPTION 59The 60.Fn gethostbyname 61and 62.Fn gethostbyaddr 63functions 64each return a pointer to an object with the 65following structure describing an internet host 66referenced by name or by address, respectively. 67This structure contains either the information obtained from the name server, 68.Xr named 8 , 69broken-out fields from a line in 70.Pa /etc/hosts , 71or database entries supplied by the 72.Xr yp 8 73system . 74If the local name server is not running these routines do a lookup in 75.Pa /etc/hosts . 76.Bd -literal 77struct hostent { 78 char *h_name; /* official name of host */ 79 char **h_aliases; /* alias list */ 80 int h_addrtype; /* host address type */ 81 int h_length; /* length of address */ 82 char **h_addr_list; /* list of addresses from name server */ 83}; 84#define h_addr h_addr_list[0] /* address, for backward compatibility */ 85.Ed 86.Pp 87The members of this structure are: 88.Bl -tag -width h_addr_list 89.It Fa h_name 90Official name of the host. 91.It Fa h_aliases 92A zero terminated array of alternate names for the host. 93.It Fa h_addrtype 94The type of address being returned; currently always 95.Dv AF_INET . 96.It Fa h_length 97The length, in bytes, of the address. 98.It Fa h_addr_list 99A zero terminated array of network addresses for the host. 100Host addresses are returned in network byte order. 101.It Fa h_addr 102The first address in 103.Fa h_addr_list ; 104this is for backward compatibility. 105.Pp 106When using the nameserver, 107.Fn gethostbyname 108will search for the named host in the current domain and its parents 109unless the name ends in a dot. 110If the name contains no dot, and if the environment variable 111.Dq Ev HOSTALIASES 112contains the name of an alias file, the alias file will first be searched 113for an alias matching the input name. 114See 115.Xr hostname 7 116for the domain search procedure and the alias file format. 117.Pp 118The 119.Fn sethostent 120function 121may be used to request the use of a connected 122.Tn TCP 123socket for queries. 124If the 125.Fa stayopen 126flag is non-zero, 127this sets the option to send all queries to the name server using 128.Tn TCP 129and to retain the connection after each call to 130.Fn gethostbyname 131or 132.Fn gethostbyaddr . 133Otherwise, queries are performed using 134.Tn UDP 135datagrams. 136.Pp 137The 138.Fn endhostent 139function 140closes the 141.Tn TCP 142connection. 143.Sh FILES 144.Bl -tag -width /etc/hosts -compact 145.It Pa /etc/hosts 146.El 147.Sh DIAGNOSTICS 148Error return status from 149.Fn gethostbyname 150and 151.Fn gethostbyaddr 152is indicated by return of a null pointer. 153The external integer 154.Va h_errno 155may then be checked to see whether this is a temporary failure 156or an invalid or unknown host. 157The routine 158.Fn herror 159can be used to print an error message describing the failure. 160If its argument 161.Fa string 162is 163.Pf non Dv -NULL , 164it is printed, followed by a colon and a space. 165The error message is printed with a trailing newline. 166.Pp 167The variable 168.Va h_errno 169can have the following values: 170.Bl -tag -width HOST_NOT_FOUND 171.It Dv HOST_NOT_FOUND 172No such host is known. 173.It Dv TRY_AGAIN 174This is usually a temporary error 175and means that the local server did not receive 176a response from an authoritative server. 177A retry at some later time may succeed. 178.It Dv NO_RECOVERY 179Some unexpected server failure was encountered. 180This is a non-recoverable error. 181.It Dv NO_DATA 182The requested name is valid but does not have an IP address; 183this is not a temporary error. 184This means that the name is known to the name server but there is no address 185associated with this name. 186Another type of request to the name server using this domain name 187will result in an answer; 188for example, a mail-forwarder may be registered for this domain. 189.El 190.Sh SEE ALSO 191.Xr resolver 3 , 192.Xr hosts 5 , 193.Xr hostname 7 , 194.Xr named 8 195.Sh CAVEAT 196The 197.Fn gethostent 198function 199is defined, and 200.Fn sethostent 201and 202.Fn endhostent 203are redefined, 204when 205.Xr libc 3 206is built to use only the routines to lookup in 207.Pa /etc/hosts 208and not the name server. 209.Pp 210The 211.Fn gethostent 212function 213reads the next line of 214.Pa /etc/hosts , 215opening the file if necessary. 216.Pp 217The 218.Fn sethostent 219function 220is redefined to open and rewind the file. If the 221.Fa stayopen 222argument is non-zero, 223the hosts data base will not be closed after each call to 224.Fn gethostbyname 225or 226.Fn gethostbyaddr . 227The 228.Fn endhostent 229function 230is redefined to close the file. 231.Sh HISTORY 232The 233.Fn herror 234function appeared in 235.Bx 4.3 . 236The 237.Fn endhostent , 238.Fn gethostbyaddr , 239.Fn gethostbyname , 240.Fn gethostent , 241and 242.Fn sethostent 243functions appeared in 244.Bx 4.2 . 245.Sh BUGS 246These functions use static data storage; 247if the data is needed for future use, it should be 248copied before any subsequent calls overwrite it. 249Only the Internet 250address format is currently understood. 251