2004-11-03 13:51:07 +00:00
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.\" Copyright 1993 David Metcalfe (david@prism.demon.co.uk)
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.\"
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.\" Permission is granted to make and distribute verbatim copies of this
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.\" manual provided the copyright notice and this permission notice are
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.\" preserved on all copies.
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.\"
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.\" Permission is granted to copy and distribute modified versions of this
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.\" manual under the conditions for verbatim copying, provided that the
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.\" entire resulting derived work is distributed under the terms of a
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.\" permission notice identical to this one.
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2007-04-12 22:42:49 +00:00
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.\"
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2004-11-03 13:51:07 +00:00
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.\" Since the Linux kernel and libraries are constantly changing, this
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.\" manual page may be incorrect or out-of-date. The author(s) assume no
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.\" responsibility for errors or omissions, or for damages resulting from
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.\" the use of the information contained herein. The author(s) may not
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.\" have taken the same level of care in the production of this manual,
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.\" which is licensed free of charge, as they might when working
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.\" professionally.
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2007-04-12 22:42:49 +00:00
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.\"
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2004-11-03 13:51:07 +00:00
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.\" Formatted or processed versions of this manual, if unaccompanied by
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.\" the source, must acknowledge the copyright and authors of this work.
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.\"
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.\" References consulted:
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.\" Linux libc source code
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.\" Lewine's _POSIX Programmer's Guide_ (O'Reilly & Associates, 1991)
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.\" 386BSD man pages
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.\" Modified 1993-05-22, David Metcalfe
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.\" Modified 1993-07-25, Rik Faith (faith@cs.unc.edu)
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.\" Modified 1997-02-16, Andries Brouwer (aeb@cwi.nl)
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.\" Modified 1998-12-21, Andries Brouwer (aeb@cwi.nl)
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.\" Modified 2000-08-12, Andries Brouwer (aeb@cwi.nl)
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.\" Modified 2001-05-19, Andries Brouwer (aeb@cwi.nl)
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.\" Modified 2002-08-05, Michael Kerrisk
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.\" Modified 2004-10-31, Andries Brouwer
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.\"
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2007-10-14 18:29:55 +00:00
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.TH GETHOSTBYNAME 3 2007-10-16 "" "Linux Programmer's Manual"
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2004-11-03 13:51:07 +00:00
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.SH NAME
|
2005-10-19 13:20:29 +00:00
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gethostbyname, gethostbyaddr, sethostent, gethostent, endhostent,
|
2007-07-08 14:31:36 +00:00
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|
herror, hstrerror,
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2007-11-24 10:30:42 +00:00
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gethostbyaddr_r,
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2007-07-08 14:31:36 +00:00
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gethostbyname2, gethostbyname2_r, gethostbyname_r,
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gethostent_r \- get network host entry
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2004-11-03 13:51:07 +00:00
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.SH SYNOPSIS
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.nf
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.B #include <netdb.h>
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.B extern int h_errno;
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.sp
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.BI "struct hostent *gethostbyname(const char *" name );
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.sp
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.BR "#include <sys/socket.h>" " /* for AF_INET */"
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2007-12-11 16:57:30 +00:00
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|
.BI "struct hostent *gethostbyaddr(const void *" addr ,
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2007-12-07 19:55:54 +00:00
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.BI " socklen_t " len ", int " type );
|
2004-11-03 13:51:07 +00:00
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.sp
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.BI "void sethostent(int " stayopen );
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.sp
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.B void endhostent(void);
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.sp
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.BI "void herror(const char *" s );
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.sp
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.BI "const char *hstrerror(int " err );
|
2007-04-03 15:32:52 +00:00
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.sp
|
2006-01-13 09:44:53 +00:00
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/* System V/POSIX extension */
|
2004-11-03 13:51:07 +00:00
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.br
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.B struct hostent *gethostent(void);
|
2007-04-03 15:32:52 +00:00
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.sp
|
2004-11-03 13:51:07 +00:00
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/* GNU extensions */
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.br
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.BI "struct hostent *gethostbyname2(const char *" name ", int " af );
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.sp
|
2007-09-20 16:26:31 +00:00
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.B "int gethostent_r("
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2007-04-03 15:32:52 +00:00
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.BI " struct hostent *" ret ", char *" buf ", size_t " buflen ,
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|
.BI " struct hostent **" result ", int *" h_errnop );
|
2004-11-03 13:51:07 +00:00
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.sp
|
2007-08-27 12:24:27 +00:00
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.BI "int gethostbyaddr_r(const void *" addr ", socklen_t " len ", int " type ,
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.BI " struct hostent *" ret ", char *" buf ", size_t " buflen ,
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|
.BI " struct hostent **" result ", int *" h_errnop );
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.sp
|
2004-11-03 13:51:07 +00:00
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.BI "int gethostbyname_r(const char *" name ,
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2007-04-03 15:32:52 +00:00
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.BI " struct hostent *" ret ", char *" buf ", size_t " buflen ,
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|
.BI " struct hostent **" result ", int *" h_errnop );
|
2004-11-03 13:51:07 +00:00
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.sp
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.BI "int gethostbyname2_r(const char *" name ", int " af,
|
2007-04-03 15:32:52 +00:00
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|
.BI " struct hostent *" ret ", char *" buf ", size_t " buflen ,
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|
.BI " struct hostent **" result ", int *" h_errnop );
|
2004-11-03 13:51:07 +00:00
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.fi
|
2007-07-08 12:11:40 +00:00
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.sp
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.in -4n
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|
Feature Test Macro Requirements for glibc (see
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|
.BR feature_test_macros (7)):
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.in
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.sp
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.ad l
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.BR gethostbyname2 (),
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.BR gethostent_r (),
|
2007-08-27 12:24:27 +00:00
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|
.BR gethostbyaddr_r (),
|
2007-07-08 12:11:40 +00:00
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|
.BR gethostbyname_r (),
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|
.BR gethostbyname2_r ():
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|
_BSD_SOURCE || _SVID_SOURCE
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|
.ad b
|
2004-11-03 13:51:07 +00:00
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|
.SH DESCRIPTION
|
2007-10-14 18:29:55 +00:00
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|
|
These functions are obsolete.
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Applications should use
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|
|
.BR getaddrinfo (3)
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and
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|
.BR getnameinfo (3)
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|
instead.
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|
2004-11-03 13:51:07 +00:00
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|
The
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|
.BR gethostbyname ()
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|
function returns a structure of type
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.I hostent
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for the given host
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|
.IR name .
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Here
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|
.I name
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|
is either a host name, or an IPv4 address in standard dot notation,
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|
|
or an IPv6 address in colon (and possibly dot) notation.
|
2005-07-20 07:50:45 +00:00
|
|
|
(See RFC\ 1884 for the description of IPv6 addresses.)
|
2004-11-03 13:51:07 +00:00
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|
|
If
|
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.I name
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|
is an IPv4 or IPv6 address, no lookup is performed and
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|
.BR gethostbyname ()
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|
simply copies
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.I name
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|
into the
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.I h_name
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field and its
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|
.I struct in_addr
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|
equivalent into the
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|
.I h_addr_list[0]
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field of the returned
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|
|
.I hostent
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structure.
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|
If
|
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.I name
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|
doesn't end in a dot and the environment variable
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|
.B HOSTALIASES
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|
is set, the alias file pointed to by
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|
.B HOSTALIASES
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|
will first be searched for
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|
.I name
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(see
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|
.BR hostname (7)
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|
for the file format).
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|
The current domain and its parents are searched unless \fIname\fP
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|
ends in a dot.
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|
.PP
|
2007-05-12 09:06:04 +00:00
|
|
|
The
|
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|
.BR gethostbyaddr ()
|
|
|
|
function returns a structure of type \fIhostent\fP
|
2004-11-03 13:51:07 +00:00
|
|
|
for the given host address \fIaddr\fP of length \fIlen\fP and address type
|
2007-04-12 22:42:49 +00:00
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|
|
\fItype\fP.
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|
|
|
Valid address types are
|
2004-11-03 13:51:07 +00:00
|
|
|
.B AF_INET
|
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|
and
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|
.BR AF_INET6 .
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|
|
The host address argument is a pointer to a struct of a type depending
|
2007-06-20 20:48:54 +00:00
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|
on the address type, for example a \fIstruct in_addr *\fP (probably
|
2007-06-21 22:55:04 +00:00
|
|
|
obtained via a call to
|
2007-05-12 13:12:02 +00:00
|
|
|
.BR inet_addr (3))
|
2007-06-22 19:42:52 +00:00
|
|
|
for address type
|
|
|
|
.BR AF_INET .
|
2004-11-03 13:51:07 +00:00
|
|
|
.PP
|
2007-05-12 09:06:04 +00:00
|
|
|
The
|
|
|
|
.BR sethostent ()
|
|
|
|
function specifies, if \fIstayopen\fP is true (1),
|
2007-04-12 22:42:49 +00:00
|
|
|
that a connected TCP socket should be used for the name server queries and
|
|
|
|
that the connection should remain open during successive queries.
|
|
|
|
Otherwise, name server queries will use UDP datagrams.
|
2004-11-03 13:51:07 +00:00
|
|
|
.PP
|
2007-05-12 09:06:04 +00:00
|
|
|
The
|
|
|
|
.BR endhostent ()
|
|
|
|
function ends the use of a TCP connection for name
|
2004-11-03 13:51:07 +00:00
|
|
|
server queries.
|
|
|
|
.PP
|
2007-05-12 09:06:04 +00:00
|
|
|
The (obsolete)
|
|
|
|
.BR herror ()
|
|
|
|
function prints the error message associated
|
2007-07-28 06:36:12 +00:00
|
|
|
with the current value of \fIh_errno\fP on \fIstderr\fP.
|
2004-11-03 13:51:07 +00:00
|
|
|
.PP
|
2007-05-12 09:06:04 +00:00
|
|
|
The (obsolete)
|
|
|
|
.BR hstrerror ()
|
|
|
|
function takes an error number
|
2004-11-03 13:51:07 +00:00
|
|
|
(typically \fIh_errno\fP) and returns the corresponding message string.
|
|
|
|
.PP
|
2007-05-12 09:06:04 +00:00
|
|
|
The domain name queries carried out by
|
|
|
|
.BR gethostbyname ()
|
|
|
|
and
|
|
|
|
.BR gethostbyaddr ()
|
|
|
|
use a combination of any or all of the name server
|
2004-11-03 13:51:07 +00:00
|
|
|
.BR named (8),
|
|
|
|
a broken out line from \fI/etc/hosts\fP, and the Network
|
|
|
|
Information Service (NIS or YP), depending upon the contents of the
|
|
|
|
\fIorder\fP line in
|
|
|
|
.IR /etc/host.conf .
|
2005-12-13 15:22:17 +00:00
|
|
|
.\" (See
|
|
|
|
.\" .BR resolv+ (8)).
|
2004-11-03 13:51:07 +00:00
|
|
|
The default action is to query
|
|
|
|
.BR named (8),
|
|
|
|
followed by
|
|
|
|
.IR /etc/hosts .
|
|
|
|
.PP
|
|
|
|
The \fIhostent\fP structure is defined in \fI<netdb.h>\fP as follows:
|
|
|
|
.sp
|
2007-12-19 05:53:30 +00:00
|
|
|
.in +4n
|
2004-11-03 13:51:07 +00:00
|
|
|
.nf
|
|
|
|
.ne 7
|
|
|
|
struct hostent {
|
2007-04-03 15:32:52 +00:00
|
|
|
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 */
|
2004-11-03 13:51:07 +00:00
|
|
|
}
|
2007-04-03 15:32:52 +00:00
|
|
|
#define h_addr h_addr_list[0] /* for backward compatibility */
|
2004-11-03 13:51:07 +00:00
|
|
|
.fi
|
2007-12-19 05:53:30 +00:00
|
|
|
.in
|
2004-11-03 13:51:07 +00:00
|
|
|
.PP
|
|
|
|
The members of the \fIhostent\fP structure are:
|
|
|
|
.TP
|
|
|
|
.I h_name
|
|
|
|
The official name of the host.
|
|
|
|
.TP
|
|
|
|
.I h_aliases
|
2006-01-13 02:09:44 +00:00
|
|
|
An array of alternative names for the host, terminated by a NULL pointer.
|
2004-11-03 13:51:07 +00:00
|
|
|
.TP
|
|
|
|
.I h_addrtype
|
|
|
|
The type of address; always
|
|
|
|
.B AF_INET
|
|
|
|
or
|
|
|
|
.B AF_INET6
|
|
|
|
at present.
|
|
|
|
.TP
|
|
|
|
.I h_length
|
|
|
|
The length of the address in bytes.
|
|
|
|
.TP
|
|
|
|
.I h_addr_list
|
2006-01-13 02:09:44 +00:00
|
|
|
An array of pointers to network addresses for the host (in network byte
|
|
|
|
order), terminated by a NULL pointer.
|
2004-11-03 13:51:07 +00:00
|
|
|
.TP
|
|
|
|
.I h_addr
|
|
|
|
The first address in \fIh_addr_list\fP for backward compatibility.
|
|
|
|
.SH "RETURN VALUE"
|
|
|
|
The
|
|
|
|
.BR gethostbyname ()
|
|
|
|
and
|
2005-10-19 07:07:02 +00:00
|
|
|
.BR gethostbyaddr ()
|
2004-11-03 13:51:07 +00:00
|
|
|
functions return the
|
|
|
|
.I hostent
|
2007-04-12 22:42:49 +00:00
|
|
|
structure or a NULL pointer if an error occurs.
|
|
|
|
On error, the
|
2004-11-03 13:51:07 +00:00
|
|
|
.I h_errno
|
|
|
|
variable holds an error number.
|
|
|
|
When non-NULL, the return value may point at static data, see the notes below.
|
|
|
|
.SH ERRORS
|
|
|
|
The variable \fIh_errno\fP can have the following values:
|
|
|
|
.TP
|
|
|
|
.B HOST_NOT_FOUND
|
|
|
|
The specified host is unknown.
|
|
|
|
.TP
|
|
|
|
.BR NO_ADDRESS " or " NO_DATA
|
|
|
|
The requested name is valid but does not have an IP address.
|
|
|
|
.TP
|
|
|
|
.B NO_RECOVERY
|
|
|
|
A non-recoverable name server error occurred.
|
|
|
|
.TP
|
|
|
|
.B TRY_AGAIN
|
2007-04-12 22:42:49 +00:00
|
|
|
A temporary error occurred on an authoritative name server.
|
|
|
|
Try again later.
|
2004-11-03 13:51:07 +00:00
|
|
|
.SH FILES
|
|
|
|
.TP
|
|
|
|
.I /etc/host.conf
|
|
|
|
resolver configuration file
|
|
|
|
.TP
|
|
|
|
.I /etc/hosts
|
|
|
|
host database file
|
2005-12-13 15:22:17 +00:00
|
|
|
.TP
|
|
|
|
.I /etc/nsswitch.conf
|
|
|
|
name service switch configuration
|
2004-11-03 13:51:07 +00:00
|
|
|
.SH "CONFORMING TO"
|
2006-08-03 13:57:30 +00:00
|
|
|
4.3BSD, POSIX.1-2001.
|
2007-05-16 17:35:34 +00:00
|
|
|
.SH NOTES
|
|
|
|
The functions
|
|
|
|
.BR gethostbyname ()
|
|
|
|
and
|
|
|
|
.BR gethostbyaddr ()
|
|
|
|
may return pointers to static data, which may be overwritten by
|
|
|
|
later calls.
|
|
|
|
Copying the
|
|
|
|
.I struct hostent
|
|
|
|
does not suffice, since it contains pointers; a deep copy is required.
|
|
|
|
.LP
|
2007-06-21 22:55:04 +00:00
|
|
|
In the original BSD implementation the
|
2007-05-26 05:56:21 +00:00
|
|
|
.I len
|
|
|
|
argument
|
2007-06-21 22:55:04 +00:00
|
|
|
of
|
2007-05-26 05:56:21 +00:00
|
|
|
.BR gethostbyname ()
|
|
|
|
was an
|
|
|
|
.IR int .
|
|
|
|
The SUSv2 standard is buggy and declares the
|
2007-05-16 17:35:34 +00:00
|
|
|
.I len
|
|
|
|
parameter of
|
|
|
|
.BR gethostbyaddr ()
|
|
|
|
to be of type
|
|
|
|
.IR size_t .
|
|
|
|
(That is wrong, because it has to be
|
|
|
|
.IR int ,
|
|
|
|
and
|
|
|
|
.I size_t
|
|
|
|
is not.
|
|
|
|
POSIX.1-2001 makes it
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.IR socklen_t ,
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which is OK.)
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2007-05-26 05:56:21 +00:00
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See also
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.BR accept (2).
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2007-05-16 17:35:34 +00:00
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.LP
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The BSD prototype for
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.BR gethostbyaddr ()
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uses
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.I const char *
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for the first argument.
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.LP
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POSIX.1-2001 marks
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.BR gethostbyaddr ()
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and
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.BR gethostbyname ()
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obsolescent.
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See
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.BR getaddrinfo (3),
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.BR getnameinfo (3),
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.BR gai_strerror (3).
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.SS "System V/POSIX Extension"
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2004-11-03 13:51:07 +00:00
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POSIX requires the
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.BR gethostent ()
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call, that should return the next entry in the host data base.
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When using DNS/BIND this does not make much sense, but it may
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be reasonable if the host data base is a file that can be read
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2007-04-12 22:42:49 +00:00
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line by line.
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On many systems a routine of this name reads
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2004-11-03 13:51:07 +00:00
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from the file
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.IR /etc/hosts .
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2007-06-08 11:56:22 +00:00
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.\" e.g., Linux, FreeBSD, Unixware, HP-UX
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2004-11-03 13:51:07 +00:00
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It may be available only when the library was built without DNS support.
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2007-06-08 11:56:22 +00:00
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.\" e.g., FreeBSD, AIX
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2007-04-12 22:42:49 +00:00
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The glibc version will ignore ipv6 entries.
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This function is not reentrant,
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2004-11-03 13:51:07 +00:00
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and glibc adds a reentrant version
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.BR gethostent_r ().
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2007-05-16 17:35:34 +00:00
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.SS "GNU Extensions"
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2004-11-03 13:51:07 +00:00
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Glibc2 also has a
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2005-10-19 07:07:02 +00:00
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.BR gethostbyname2 ()
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2004-11-03 13:51:07 +00:00
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that works like
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2005-10-19 07:07:02 +00:00
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.BR gethostbyname (),
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2004-11-03 13:51:07 +00:00
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but permits to specify the address family to which the address must belong.
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.LP
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Glibc2 also has reentrant versions
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2007-08-27 12:24:27 +00:00
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.BR gethostent_r (),
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.BR gethostbyaddr_r (),
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2005-10-19 07:07:02 +00:00
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.BR gethostbyname_r ()
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2004-11-03 13:51:07 +00:00
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and
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2005-10-19 07:07:02 +00:00
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.BR gethostbyname2_r ().
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2007-09-10 04:17:16 +00:00
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The caller supplies a
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.I hostent
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structure
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2007-08-27 12:24:27 +00:00
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.I ret
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2007-09-10 04:17:16 +00:00
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which will be filled in on success, and a temporary work buffer
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2004-11-03 13:51:07 +00:00
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.I buf
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2007-08-27 12:24:27 +00:00
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of size
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2004-11-03 13:51:07 +00:00
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.IR buflen .
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2007-08-27 12:24:27 +00:00
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After the call,
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.I result
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will point to the result on success. In case of an error
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or if no entry is found
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.I result
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2007-09-10 04:17:16 +00:00
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will be NULL.
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2007-08-27 12:24:27 +00:00
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The functions return 0 on success and a non-zero error number on failure.
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In addition to the errors returned by the non-reentrant
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versions of these functions, if
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.I buf
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is too small, the functions will return
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.BR ERANGE ,
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and the call should be retried with a larger buffer.
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The global variable
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2004-11-03 13:51:07 +00:00
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.I h_errno
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2007-08-27 12:24:27 +00:00
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is not modified, but the address of a variable in which to store error numbers
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2004-11-03 13:51:07 +00:00
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is passed in
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.IR h_errnop .
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.SH "SEE ALSO"
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.BR getaddrinfo (3),
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2007-10-14 18:16:34 +00:00
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.\" .BR getipnodebyaddr (3),
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.\" .BR getipnodebyname (3),
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2004-11-03 13:51:07 +00:00
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.BR getnameinfo (3),
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.BR inet_ntop (3),
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.BR inet_pton (3),
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.BR resolver (3),
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.BR hosts (5),
|
2005-12-13 15:22:17 +00:00
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.BR nsswitch.conf (5),
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2004-11-03 13:51:07 +00:00
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.BR hostname (7),
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2005-12-13 15:22:17 +00:00
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.BR named (8)
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.\" .BR resolv+ (8)
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