Provided by: manpages-dev_2.77-1_all bug


       gethostbyname,   gethostbyaddr,   sethostent,  gethostent,  endhostent,
       herror, hstrerror, gethostbyaddr_r,  gethostbyname2,  gethostbyname2_r,
       gethostbyname_r, gethostent_r - get network host entry


       #include <netdb.h>
       extern int h_errno;

       struct hostent *gethostbyname(const char *name);

       #include <sys/socket.h>       /* for AF_INET */
       struct hostent *gethostbyaddr(const void *addr,
                                     socklen_t len, int type);

       void sethostent(int stayopen);

       void endhostent(void);

       void herror(const char *s);

       const char *hstrerror(int err);

       /* System V/POSIX extension */
       struct hostent *gethostent(void);

       /* GNU extensions */
       struct hostent *gethostbyname2(const char *name, int af);

       int gethostent_r(
               struct hostent *ret, char *buf, size_t buflen,
               struct hostent **result, int *h_errnop);

       int gethostbyaddr_r(const void *addr, socklen_t len, int type,
               struct hostent *ret, char *buf, size_t buflen,
               struct hostent **result, int *h_errnop);

       int gethostbyname_r(const char *name,
               struct hostent *ret, char *buf, size_t buflen,
               struct hostent **result, int *h_errnop);

       int gethostbyname2_r(const char *name, int af,
               struct hostent *ret, char *buf, size_t buflen,
               struct hostent **result, int *h_errnop);

   Feature Test Macro Requirements for glibc (see feature_test_macros(7)):

       gethostbyname2(), gethostent_r(), gethostbyaddr_r(), gethostbyname_r(),
       gethostbyname2_r(): _BSD_SOURCE || _SVID_SOURCE


       These functions are obsolete.  Applications should  use  getaddrinfo(3)
       and getnameinfo(3) instead.

       The  gethostbyname()  function  returns a structure of type hostent for
       the given host name.  Here name is either  a  host  name,  or  an  IPv4
       address  in  standard  dot  notation,  or an IPv6 address in colon (and
       possibly dot) notation.  (See RFC 1884  for  the  description  of  IPv6
       addresses.)  If name is an IPv4 or IPv6 address, no lookup is performed
       and gethostbyname() simply copies name into the h_name  field  and  its
       struct in_addr equivalent into the h_addr_list[0] field of the returned
       hostent structure.  If name doesn’t end in a dot  and  the  environment
       variable  HOSTALIASES  is set, the alias file pointed to by HOSTALIASES
       will first be searched for name (see hostname(7) for the file  format).
       The  current  domain and its parents are searched unless name ends in a

       The gethostbyaddr() function returns a structure of  type  hostent  for
       the given host address addr of length len and address type type.  Valid
       address types are AF_INET and AF_INET6.  The host address argument is a
       pointer  to  a  struct  of  a  type  depending on the address type, for
       example  a  struct  in_addr  *  (probably  obtained  via  a   call   to
       inet_addr(3)) for address type AF_INET.

       The  sethostent()  function  specifies, if stayopen is true (1), 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.

       The endhostent() function ends the use of a  TCP  connection  for  name
       server queries.

       The  (obsolete)  herror()  function prints the error message associated
       with the current value of h_errno on stderr.

       The (obsolete) hstrerror() function takes an  error  number  (typically
       h_errno) and returns the corresponding message string.

       The   domain   name   queries   carried   out  by  gethostbyname()  and
       gethostbyaddr() use a combination of any or  all  of  the  name  server
       named(8),   a   broken  out  line  from  /etc/hosts,  and  the  Network
       Information Service (NIS or YP), depending upon  the  contents  of  the
       order line in /etc/host.conf.  The default action is to query named(8),
       followed by /etc/hosts.

       The hostent structure is defined in <netdb.h> as follows:

           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 */
           #define h_addr h_addr_list[0] /* for backward compatibility */

       The members of the hostent structure are:

       h_name The official name of the host.

              An array of alternative names for the host, terminated by a NULL

              The type of address; always AF_INET or AF_INET6 at present.

              The length of the address in bytes.

              An  array  of  pointers  to  network  addresses for the host (in
              network byte order), terminated by a NULL pointer.

       h_addr The first address in h_addr_list for backward compatibility.


       The gethostbyname() and gethostbyaddr() functions  return  the  hostent
       structure  or a NULL pointer if an error occurs.  On error, the h_errno
       variable holds an error number.  When non-NULL, the  return  value  may
       point at static data, see the notes below.


       The variable h_errno can have the following values:

              The specified host is unknown.

              The requested name is valid but does not have an IP address.

              A non-recoverable name server error occurred.

              A temporary error occurred on an authoritative name server.  Try
              again later.


              resolver configuration file

              host database file

              name service switch configuration


       4.3BSD, POSIX.1-2001.


       The functions gethostbyname() and gethostbyaddr() may  return  pointers
       to  static  data, which may be overwritten by later calls.  Copying the
       struct hostent does not suffice, since it  contains  pointers;  a  deep
       copy is required.

       In  the original BSD implementation the len argument of gethostbyname()
       was an int.  The SUSv2 standard is buggy and declares the len parameter
       of  gethostbyaddr()  to  be of type size_t.  (That is wrong, because it
       has to be int, and size_t is not.   POSIX.1-2001  makes  it  socklen_t,
       which is OK.)  See also accept(2).

       The  BSD  prototype for gethostbyaddr() uses const char * for the first

       POSIX.1-2001 marks  gethostbyaddr()  and  gethostbyname()  obsolescent.
       See getaddrinfo(3), getnameinfo(3), gai_strerror(3).

   System V/POSIX Extension
       POSIX requires the gethostent() call, that should return the next entry
       in the host data base.  When using DNS/BIND this  does  not  make  much
       sense,  but  it  may be reasonable if the host data base is a file that
       can be read line by line.  On many systems a routine of this name reads
       from  the  file  /etc/hosts.  It may be available only when the library
       was built without DNS support.  The  glibc  version  will  ignore  ipv6
       entries.   This  function  is not reentrant, and glibc adds a reentrant
       version gethostent_r().

   GNU Extensions
       Glibc2 also has a gethostbyname2() that works like gethostbyname(), but
       permits to specify the address family to which the address must belong.

       Glibc2 also has reentrant versions  gethostent_r(),  gethostbyaddr_r(),
       gethostbyname_r()   and  gethostbyname2_r().   The  caller  supplies  a
       hostent structure ret which  will  be  filled  in  on  success,  and  a
       temporary  work buffer buf of size buflen.  After the call, result will
       point to the result on success.  In case of an error or if no entry  is
       found  result  will  be  NULL.  The functions return 0 on success and a
       nonzero error number on failure.  In addition to the errors returned by
       the non-reentrant versions of these functions, if buf is too small, the
       functions will return ERANGE, and the call should  be  retried  with  a
       larger  buffer.   The  global variable h_errno is not modified, but the
       address of a variable in which to store  error  numbers  is  passed  in


       getaddrinfo(3),     getnameinfo(3),     inet_ntop(3),     inet_pton(3),
       resolver(3), hosts(5), nsswitch.conf(5), hostname(7), named(8)


       This page is part of release 2.77 of the Linux  man-pages  project.   A
       description  of  the project, and information about reporting bugs, can
       be found at

                                  2007-10-16                  GETHOSTBYNAME(3)