.\" Copyright (c) 1983, 1987, 1991 The Regents of the University of California. .\" All rights reserved. .\" .\" Redistribution and use in source and binary forms, with or without .\" modification, are permitted provided that the following conditions .\" are met: .\" 1. Redistributions of source code must retain the above copyright .\" notice, this list of conditions and the following disclaimer. .\" 2. Redistributions in binary form must reproduce the above copyright .\" notice, this list of conditions and the following disclaimer in the .\" documentation and/or other materials provided with the distribution. .\" 3. All advertising materials mentioning features or use of this software .\" must display the following acknowledgement: .\" This product includes software developed by the University of .\" California, Berkeley and its contributors. .\" 4. Neither the name of the University nor the names of its contributors .\" may be used to endorse or promote products derived from this software .\" without specific prior written permission. .\" .\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND .\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE .\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE .\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE .\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL .\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS .\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) .\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT .\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY .\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF .\" SUCH DAMAGE. .\" .\" from: @(#)gethostbyname.3 6.14 (Berkeley) 7/31/91 .\" $Id: gethostbyname.3,v 1.4 1994/03/12 09:00:01 davidb Exp $ .\" .Dd July 31, 1991 .Dt GETHOSTBYNAME 3 .Os BSD 4.2 .Sh NAME .Nm gethostbyname , .Nm gethostbyaddr , .Nm gethostent , .Nm sethostent , .Nm endhostent , .Nm herror .Nd get network host entry .Sh SYNOPSIS .Fd #include .Fd extern int h_errno; .Ft struct hostent * .Fn gethostbyname "char *name" .Ft struct hostent * .Fn gethostbyaddr "char *addr" "int len" "int type" .Ft struct hostent * .Fn gethostent void .Fn sethostent "int stayopen" .Fn endhostent void .Fn herror "char *string" .Sh DESCRIPTION The .Fn gethostbyname and .Fn gethostbyaddr functions each return a pointer to an object with the following structure describing an internet host referenced by name or by address, respectively. This structure contains either the information obtained from the name server, .Xr named 8 , or broken-out fields from a line in .Pa /etc/hosts . If the local name server is not running these routines do a lookup in .Pa /etc/hosts . .Bd -literal struct hostent { char *h_name; /* official name of host */ char **h_aliases; /* alias list */ int h_addrtype; /* host address type */ int h_length; /* length of address */ char **h_addr_list; /* list of addresses from name server */ }; #define h_addr h_addr_list[0] /* address, for backward compatibility */ .Ed .Pp The members of this structure are: .Bl -tag -width h_addr_list .It Fa h_name Official name of the host. .It Fa h_aliases A zero terminated array of alternate names for the host. .It Fa h_addrtype The type of address being returned; currently always .Dv AF_INET . .It Fa h_length The length, in bytes, of the address. .It Fa h_addr_list A zero terminated array of network addresses for the host. Host addresses are returned in network byte order. .It Fa h_addr The first address in .Fa h_addr_list ; this is for backward compatibility. .Pp When using the nameserver, .Fn gethostbyname will search for the named host in the current domain and its parents unless the name ends in a dot. If the name contains no dot, and if the environment variable .Dq Ev HOSTALIASES contains the name of an alias file, the alias file will first be searched for an alias matching the input name. See .Xr hostname 7 for the domain search procedure and the alias file format. .Pp The .Fn sethostent function may be used to request the use of a connected .Tn TCP socket for queries. If the .Fa stayopen flag is non-zero, this sets the option to send all queries to the name server using .Tn TCP and to retain the connection after each call to .Fn gethostbyname or .Fn gethostbyaddr . Otherwise, queries are performed using .Tn UDP datagrams. .Pp The .Fn endhostent function closes the .Tn TCP connection. .Sh FILES .Bl -tag -width /etc/hosts -compact .It Pa /etc/hosts .El .Sh DIAGNOSTICS Error return status from .Fn gethostbyname and .Fn gethostbyaddr is indicated by return of a null pointer. The external integer .Va h_errno may then be checked to see whether this is a temporary failure or an invalid or unknown host. The routine .Fn herror can be used to print an error message describing the failure. If its argument .Fa string is .Pf non Dv -NULL , it is printed, followed by a colon and a space. The error message is printed with a trailing newline. .Pp The variable .Va h_errno can have the following values: .Bl -tag -width HOST_NOT_FOUND .It Dv HOST_NOT_FOUND No such host is known. .It Dv TRY_AGAIN This is usually a temporary error and means that the local server did not receive a response from an authoritative server. A retry at some later time may succeed. .It Dv NO_RECOVERY Some unexpected server failure was encountered. This is a non-recoverable error. .It Dv NO_DATA The requested name is valid but does not have an IP address; this is not a temporary error. This means that the name is known to the name server but there is no address associated with this name. Another type of request to the name server using this domain name will result in an answer; for example, a mail-forwarder may be registered for this domain. .El .Sh SEE ALSO .Xr resolver 3 , .Xr hosts 5 , .Xr hostname 7 , .Xr named 8 .Sh CAVEAT The .Fn gethostent function is defined, and .Fn sethostent and .Fn endhostent are redefined, when .Xr libc 3 is built to use only the routines to lookup in .Pa /etc/hosts and not the name server. .Pp The .Fn gethostent function reads the next line of .Pa /etc/hosts , opening the file if necessary. .Pp The .Fn sethostent function is redefined to open and rewind the file. If the .Fa stayopen argument is non-zero, the hosts data base will not be closed after each call to .Fn gethostbyname or .Fn gethostbyaddr . The .Fn endhostent function is redefined to close the file. .Sh HISTORY The .Fn herror function appeared in .Bx 4.3 . The .Fn endhostent , .Fn gethostbyaddr , .Fn gethostbyname , .Fn gethostent , and .Fn sethostent functions appeared in .Bx 4.2 . .Sh BUGS These functions use static data storage; if the data is needed for future use, it should be copied before any subsequent calls overwrite it. Only the Internet address format is currently understood.