250 lines
6.8 KiB
Groff
250 lines
6.8 KiB
Groff
.\" Copyright (c) 1983, 1987, 1991, 1993
|
|
.\" 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.
|
|
.\"
|
|
.\" @(#)gethostbyname.3 8.2 (Berkeley) 4/19/94
|
|
.\"
|
|
.Dd April 19, 1994
|
|
.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 <netdb.h>
|
|
.Fd extern struct 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
|
|
opens and/or rewinds the file
|
|
.Pa /etc/hosts .
|
|
If the
|
|
.Fa stayopen
|
|
argument is non-zero,
|
|
the file will not be closed after each call to
|
|
.Fn gethostbyname
|
|
or
|
|
.Fn gethostbyaddr .
|
|
.Pp
|
|
The
|
|
.Fn endhostent
|
|
function
|
|
closes 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.
|