247 lines
6.8 KiB
Groff
247 lines
6.8 KiB
Groff
.\" Copyright (c) 1983, 1987 The Regents of the University of California.
|
|
.\" All rights reserved.
|
|
.\"
|
|
.\" Redistribution and use in source and binary forms are permitted provided
|
|
.\" that: (1) source distributions retain this entire copyright notice and
|
|
.\" comment, and (2) distributions including binaries display the following
|
|
.\" acknowledgement: ``This product includes software developed by the
|
|
.\" University of California, Berkeley and its contributors'' in the
|
|
.\" documentation or other materials provided with the distribution and in
|
|
.\" all advertising materials mentioning features or use of this software.
|
|
.\" 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 ``AS IS'' AND WITHOUT ANY EXPRESS OR IMPLIED
|
|
.\" WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED WARRANTIES OF
|
|
.\" MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE.
|
|
.\"
|
|
.\" @(#)gethostbyname.3 6.12 (Berkeley) 6/23/90
|
|
.\"
|
|
.Dd June 23, 1990
|
|
.Dt GETHOSTBYNAME @LIB_NETWORK_EXT_U@
|
|
.Os BSD 4
|
|
.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>
|
|
.Ft extern int
|
|
.Fa h_errno;
|
|
.Pp
|
|
.Ft struct hostent *
|
|
.Fn gethostbyname "char *name";
|
|
.Ft struct hostent *
|
|
.Fn gethostbyname2 "char *name" "int af";
|
|
.Ft struct hostent *
|
|
.Fn gethostbyaddr "char *addr" "int len, type";
|
|
.Ft struct hostent *
|
|
.Fn gethostent
|
|
.Fn sethostent "int stayopen";
|
|
.Fn endhostent
|
|
.Fn herror "char *string";
|
|
.Sh DESCRIPTION
|
|
.Fn Gethostbyname ,
|
|
.Fn gethostbyname2 ,
|
|
and
|
|
.Fn gethostbyaddr
|
|
each return a pointer to a
|
|
.Ft hostent
|
|
structure (see below) describing an internet host
|
|
referenced by name or by address, as the function names indicate.
|
|
This structure contains either the information obtained from the name server,
|
|
.Xr @INDOT@named @SYS_OPS_EXT@ ,
|
|
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 -offset indent
|
|
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 h_name
|
|
Official name of the host.
|
|
.It h_aliases
|
|
A zero-terminated array of alternate names for the host.
|
|
.It h_addrtype
|
|
The type of address being returned; usually
|
|
.Dv AF_INET .
|
|
.It h_length
|
|
The length, in bytes, of the address.
|
|
.It h_addr_list
|
|
A zero-terminated array of network addresses for the host.
|
|
Host addresses are returned in network byte order.
|
|
.It h_addr
|
|
The first address in
|
|
.Li h_addr_list ;
|
|
this is for backward compatibility.
|
|
.El
|
|
.Pp
|
|
When using the nameserver,
|
|
.Fn gethostbyname
|
|
will search for the named host in each parent domain given in the
|
|
.Dq Li search
|
|
directive of
|
|
.Xr resolv.conf @FORMAT_EXT@
|
|
unless the name contains a dot
|
|
.Pq Dq \&. .
|
|
If the name contains no dot, and if the environment variable
|
|
.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 @DESC_EXT@
|
|
for the domain search procedure and the alias file format.
|
|
.Pp
|
|
.Fn Gethostbyname2
|
|
is an evolution of
|
|
.Fn gethostbyname
|
|
intended to allow lookups in address families other than
|
|
.Dv AF_INET ,
|
|
for example,
|
|
.Dv AF_INET6 .
|
|
Currently, the
|
|
.Fa af
|
|
argument must be specified as
|
|
.Dv AF_INET
|
|
else the function will return
|
|
.Dv NULL
|
|
after having set
|
|
.Ft h_errno
|
|
to
|
|
.Dv NETDB_INTERNAL .
|
|
.Pp
|
|
.Fn Sethostent
|
|
may be used to request the use of a connected 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 TCP
|
|
and to retain the connection after each call to
|
|
.Fn gethostbyname
|
|
or
|
|
.Fn gethostbyaddr .
|
|
Otherwise, queries are performed using UDP datagrams.
|
|
.Pp
|
|
.Fn Endhostent
|
|
closes the TCP connection.
|
|
.Sh ENVIRONMENT
|
|
.Bl -tag -width "HOSTALIASES " -compress
|
|
.It Ev HOSTALIASES
|
|
Name of file containing
|
|
.Pq Ar host alias , full hostname
|
|
pairs.
|
|
.El
|
|
.Sh FILES
|
|
.Bl -tag -width "HOSTALIASES " -compress
|
|
.It Pa /etc/hosts
|
|
See
|
|
.Xr hosts @FORMAT_EXT@ .
|
|
.It Ev HOSTALIASES
|
|
Name of file containing
|
|
.Pq Ar host alias , full hostname
|
|
pairs.
|
|
.El
|
|
.Sh DIAGNOSTICS
|
|
.Pp
|
|
Error return status from
|
|
.Fn gethostbyname
|
|
and
|
|
.Fn gethostbyaddr
|
|
is indicated by return of a null pointer.
|
|
The external integer
|
|
.Ft 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 non-NULL, it is printed, followed by a colon and a space.
|
|
The error message is printed with a trailing newline.
|
|
.Pp
|
|
.Ft h_errno
|
|
can have the following values:
|
|
.Bl -tag -width "HOST_NOT_FOUND " -offset indent
|
|
.It Dv NETDB_INTERNAL
|
|
This indicates an internal error in the library, unrelated to the network
|
|
or name service.
|
|
.Ft errno
|
|
will be valid in this case; see
|
|
.Xr perror @SYSCALL_EXT@ .
|
|
.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, as one might expect.
|
|
.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 hosts @FORMAT_EXT@ ,
|
|
.Xr hostname @DESC_EXT@ ,
|
|
.Xr @INDOT@named @SYS_OPS_EXT@ ,
|
|
.Xr resolver @LIB_NETWORK_EXT@ ,
|
|
.Xr resolver @FORMAT_EXT@ .
|
|
.Sh CAVEAT
|
|
.Pp
|
|
.Fn Gethostent
|
|
is defined, and
|
|
.Fn sethostent
|
|
and
|
|
.Fn endhostent
|
|
are redefined,
|
|
when
|
|
.Pa libc
|
|
is built to use only the routines to lookup in
|
|
.Pa /etc/hosts
|
|
and not the name server:
|
|
.Bd -filled -offset indent
|
|
.Pp
|
|
.Fn Gethostent
|
|
reads the next line of
|
|
.Pa /etc/hosts ,
|
|
opening the file if necessary.
|
|
.Pp
|
|
.Fn Sethostent
|
|
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 .
|
|
.Pp
|
|
.Fn Endhostent
|
|
is redefined to close the file.
|
|
.Ed
|
|
.Sh BUGS
|
|
All information is contained in a static area so it must be copied if it is
|
|
to be saved. Only the Internet address format is currently understood.
|