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 1.2 1993/08/01 07:45:22 mycroft 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 struct h_errno; 49.Ft struct hostent * 50.Fn gethostbyname "char *name" 51.Ft struct hostent * 52.Fn gethostbyaddr "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 , 69or broken-out fields from a line in 70.Pa /etc/hosts . 71If the local name server is not running these routines do a lookup in 72.Pa /etc/hosts . 73.Bd -literal 74struct hostent { 75 char *h_name; /* official name of host */ 76 char **h_aliases; /* alias list */ 77 int h_addrtype; /* host address type */ 78 int h_length; /* length of address */ 79 char **h_addr_list; /* list of addresses from name server */ 80}; 81#define h_addr h_addr_list[0] /* address, for backward compatibility */ 82.Ed 83.Pp 84The members of this structure are: 85.Bl -tag -width h_addr_list 86.It Fa h_name 87Official name of the host. 88.It Fa h_aliases 89A zero terminated array of alternate names for the host. 90.It Fa h_addrtype 91The type of address being returned; currently always 92.Dv AF_INET . 93.It Fa h_length 94The length, in bytes, of the address. 95.It Fa h_addr_list 96A zero terminated array of network addresses for the host. 97Host addresses are returned in network byte order. 98.It Fa h_addr 99The first address in 100.Fa h_addr_list ; 101this is for backward compatiblity. 102.Pp 103When using the nameserver, 104.Fn gethostbyname 105will search for the named host in the current domain and its parents 106unless the name ends in a dot. 107If the name contains no dot, and if the environment variable 108.Dq Ev HOSTALIASES 109contains the name of an alias file, the alias file will first be searched 110for an alias matching the input name. 111See 112.Xr hostname 7 113for the domain search procedure and the alias file format. 114.Pp 115The 116.Fn sethostent 117function 118may be used to request the use of a connected 119.Tn TCP 120socket for queries. 121If the 122.Fa stayopen 123flag is non-zero, 124this sets the option to send all queries to the name server using 125.Tn TCP 126and to retain the connection after each call to 127.Fn gethostbyname 128or 129.Fn gethostbyaddr . 130Otherwise, queries are performed using 131.Tn UDP 132datagrams. 133.Pp 134The 135.Fn endhostent 136function 137closes the 138.Tn TCP 139connection. 140.Sh FILES 141.Bl -tag -width /etc/hosts -compact 142.It Pa /etc/hosts 143.El 144.Sh DIAGNOSTICS 145Error return status from 146.Fn gethostbyname 147and 148.Fn gethostbyaddr 149is indicated by return of a null pointer. 150The external integer 151.Va h_errno 152may then be checked to see whether this is a temporary failure 153or an invalid or unknown host. 154The routine 155.Fn herror 156can be used to print an error message describing the failure. 157If its argument 158.Fa string 159is 160.Pf non Dv -NULL , 161it is printed, followed by a colon and a space. 162The error message is printed with a trailing newline. 163.Pp 164The variable 165.Va h_errno 166can have the following values: 167.Bl -tag -width HOST_NOT_FOUND 168.It Dv HOST_NOT_FOUND 169No such host is known. 170.It Dv TRY_AGAIN 171This is usually a temporary error 172and means that the local server did not receive 173a response from an authoritative server. 174A retry at some later time may succeed. 175.It Dv NO_RECOVERY 176Some unexpected server failure was encountered. 177This is a non-recoverable error. 178.It Dv NO_DATA 179The requested name is valid but does not have an IP address; 180this is not a temporary error. 181This means that the name is known to the name server but there is no address 182associated with this name. 183Another type of request to the name server using this domain name 184will result in an answer; 185for example, a mail-forwarder may be registered for this domain. 186.El 187.Sh SEE ALSO 188.Xr resolver 3 , 189.Xr hosts 5 , 190.Xr hostname 7 , 191.Xr named 8 192.Sh CAVEAT 193The 194.Fn gethostent 195function 196is defined, and 197.Fn sethostent 198and 199.Fn endhostent 200are redefined, 201when 202.Xr libc 3 203is built to use only the routines to lookup in 204.Pa /etc/hosts 205and not the name server. 206.Pp 207The 208.Fn gethostent 209function 210reads the next line of 211.Pa /etc/hosts , 212opening the file if necessary. 213.Pp 214The 215.Fn sethostent 216function 217is redefined to open and rewind the file. If the 218.Fa stayopen 219argument is non-zero, 220the hosts data base will not be closed after each call to 221.Fn gethostbyname 222or 223.Fn gethostbyaddr . 224The 225.Fn endhostent 226function 227is redefined to close the file. 228.Sh HISTORY 229The 230.Fn herror 231function appeared in 232.Bx 4.3 . 233The 234.Fn endhostent , 235.Fn gethostbyaddr , 236.Fn gethostbyname , 237.Fn gethostent , 238and 239.Fn sethostent 240functions appeared in 241.Bx 4.2 . 242.Sh BUGS 243These functions use static data storage; 244if the data is needed for future use, it should be 245copied before any subsequent calls overwrite it. 246Only the Internet 247address format is currently understood. 248