1 .\" Copyright 1993 David Metcalfe (david@prism.demon.co.uk)
3 .\" Permission is granted to make and distribute verbatim copies of this
4 .\" manual provided the copyright notice and this permission notice are
5 .\" preserved on all copies.
7 .\" Permission is granted to copy and distribute modified versions of this
8 .\" manual under the conditions for verbatim copying, provided that the
9 .\" entire resulting derived work is distributed under the terms of a
10 .\" permission notice identical to this one.
12 .\" Since the Linux kernel and libraries are constantly changing, this
13 .\" manual page may be incorrect or out-of-date. The author(s) assume no
14 .\" responsibility for errors or omissions, or for damages resulting from
15 .\" the use of the information contained herein. The author(s) may not
16 .\" have taken the same level of care in the production of this manual,
17 .\" which is licensed free of charge, as they might when working
20 .\" Formatted or processed versions of this manual, if unaccompanied by
21 .\" the source, must acknowledge the copyright and authors of this work.
23 .\" References consulted:
24 .\" Linux libc source code
25 .\" Lewine's _POSIX Programmer's Guide_ (O'Reilly & Associates, 1991)
27 .\" Modified 1993-05-22, David Metcalfe
28 .\" Modified 1993-07-25, Rik Faith (faith@cs.unc.edu)
29 .\" Modified 1997-02-16, Andries Brouwer (aeb@cwi.nl)
30 .\" Modified 1998-12-21, Andries Brouwer (aeb@cwi.nl)
31 .\" Modified 2000-08-12, Andries Brouwer (aeb@cwi.nl)
32 .\" Modified 2001-05-19, Andries Brouwer (aeb@cwi.nl)
33 .\" Modified 2002-08-05, Michael Kerrisk
34 .\" Modified 2004-10-31, Andries Brouwer
36 .TH GETHOSTBYNAME 3 2004-10-31 "" "Linux Programmer's Manual"
38 gethostbyname, gethostbyaddr, sethostent, gethostent, endhostent,
39 herror, hstrerror \- get network host entry
43 .B extern int h_errno;
45 .BI "struct hostent *gethostbyname(const char *" name );
47 .BR "#include <sys/socket.h>" " /* for AF_INET */"
48 .BI "struct hostent *gethostbyaddr(const void *" addr \
49 ", socklen_t " len ", int " type );
51 .BI "void sethostent(int " stayopen );
53 .B void endhostent(void);
55 .BI "void herror(const char *" s );
57 .BI "const char *hstrerror(int " err );
59 /* System V/POSIX extension */
61 .B struct hostent *gethostent(void);
65 .BI "struct hostent *gethostbyname2(const char *" name ", int " af );
67 .BI "int gethostent_r("
68 .BI " struct hostent *" ret ", char *" buf ", size_t " buflen ,
69 .BI " struct hostent **" result ", int *" h_errnop );
71 .BI "int gethostbyname_r(const char *" name ,
72 .BI " struct hostent *" ret ", char *" buf ", size_t " buflen ,
73 .BI " struct hostent **" result ", int *" h_errnop );
75 .BI "int gethostbyname2_r(const char *" name ", int " af,
76 .BI " struct hostent *" ret ", char *" buf ", size_t " buflen ,
77 .BI " struct hostent **" result ", int *" h_errnop );
82 function returns a structure of type
88 is either a host name, or an IPv4 address in standard dot notation,
89 or an IPv6 address in colon (and possibly dot) notation.
90 (See RFC\ 1884 for the description of IPv6 addresses.)
93 is an IPv4 or IPv6 address, no lookup is performed and
103 field of the returned
108 doesn't end in a dot and the environment variable
110 is set, the alias file pointed to by
112 will first be searched for
116 for the file format).
117 The current domain and its parents are searched unless \fIname\fP
122 function returns a structure of type \fIhostent\fP
123 for the given host address \fIaddr\fP of length \fIlen\fP and address type
125 Valid address types are
129 The host address argument is a pointer to a struct of a type depending
130 on the address type, for example a \fIstruct in_addr *\fP (probably
131 obtained via a call to
133 for address type AF_INET.
137 function specifies, if \fIstayopen\fP is true (1),
138 that a connected TCP socket should be used for the name server queries and
139 that the connection should remain open during successive queries.
140 Otherwise, name server queries will use UDP datagrams.
144 function ends the use of a TCP connection for name
149 function prints the error message associated
150 with the current value of \fIh_errno\fP on \fIstderr\fp.
154 function takes an error number
155 (typically \fIh_errno\fP) and returns the corresponding message string.
157 The domain name queries carried out by
161 use a combination of any or all of the name server
163 a broken out line from \fI/etc/hosts\fP, and the Network
164 Information Service (NIS or YP), depending upon the contents of the
168 .\" .BR resolv+ (8)).
169 The default action is to query
174 The \fIhostent\fP structure is defined in \fI<netdb.h>\fP as follows:
180 char *h_name; /* official name of host */
181 char **h_aliases; /* alias list */
182 int h_addrtype; /* host address type */
183 int h_length; /* length of address */
184 char **h_addr_list; /* list of addresses */
186 #define h_addr h_addr_list[0] /* for backward compatibility */
190 The members of the \fIhostent\fP structure are:
193 The official name of the host.
196 An array of alternative names for the host, terminated by a NULL pointer.
199 The type of address; always
206 The length of the address in bytes.
209 An array of pointers to network addresses for the host (in network byte
210 order), terminated by a NULL pointer.
213 The first address in \fIh_addr_list\fP for backward compatibility.
221 structure or a NULL pointer if an error occurs.
224 variable holds an error number.
225 When non-NULL, the return value may point at static data, see the notes below.
227 The variable \fIh_errno\fP can have the following values:
230 The specified host is unknown.
232 .BR NO_ADDRESS " or " NO_DATA
233 The requested name is valid but does not have an IP address.
236 A non-recoverable name server error occurred.
239 A temporary error occurred on an authoritative name server.
244 resolver configuration file
249 .I /etc/nsswitch.conf
250 name service switch configuration
252 4.3BSD, POSIX.1-2001.
258 may return pointers to static data, which may be overwritten by
262 does not suffice, since it contains pointers; a deep copy is required.
264 In the original BSD implementation the
271 The SUSv2 standard is buggy and declares the
277 (That is wrong, because it has to be
282 POSIX.1-2001 makes it
288 The BSD prototype for
292 for the first argument.
302 .BR gai_strerror (3).
303 .SS "System V/POSIX Extension"
306 call, that should return the next entry in the host data base.
307 When using DNS/BIND this does not make much sense, but it may
308 be reasonable if the host data base is a file that can be read
310 On many systems a routine of this name reads
313 .\" e.g., Linux, FreeBSD, Unixware, HP-UX
314 It may be available only when the library was built without DNS support.
315 .\" e.g., FreeBSD, AIX
316 The glibc version will ignore ipv6 entries.
317 This function is not reentrant,
318 and glibc adds a reentrant version
322 .BR gethostbyname2 ()
324 .BR gethostbyname (),
325 but permits to specify the address family to which the address must belong.
327 Glibc2 also has reentrant versions
328 .BR gethostbyname_r ()
330 .BR gethostbyname2_r ().
331 These return 0 on success and non-zero on error.
332 The result of the call
333 is now stored in the struct with address
337 will be NULL on error or point to the result on success.
338 Auxiliary data is stored in the buffer
342 (If the buffer is too small, these functions will return
346 is modified, but the address of a variable in which to store error numbers
351 .BR getipnodebyaddr (3),
352 .BR getipnodebyname (3),
358 .BR nsswitch.conf (5),