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gethostbyname(3)
NAME
  gethostbyname, gethostbyname_r - Get a network host entry by name

LIBRARY
  Standard C Library (libc.so, libc.a)

SYNOPSIS
  #include <netdb.h>

  struct hostent *gethostbyname(
	  const char *name);

  [Digital]  The following function is supported in order to maintain
  backward compatibility with previous versions of the operating system.  You
  should not use it in new designs.

  int gethostbyname_r(
	  const char *name,
	  struct hostent *hptr,
	  struct hostent_data *hdptr);

STANDARDS
  Interfaces documented on this reference page conform to industry standards
  as follows:

  gethostbyname():  XPG4-UNIX

  Refer to the standards(5) reference page for more information about
  industry standards and associated tags.

PARAMETERS
  name	    Specifies the official network name or alias.

  hptr	    [Digital]  For gethostbyname_r() only, this points to the hostent
	    structure.	The netdb.h header file defines hostent structure.

  hdptr	    [Digital]  For gethostbyname_r() only, this is data for hosts
	    database.  The netdb.h header file defines hostent_data
	    structure.

DESCRIPTION
  The gethostbyname() function returns a pointer to a structure of type
  hostent. Its members specify data obtained from either the local /etc/hosts
  file or one of the files distributed by BIND or NIS.	To determine which
  file or files to search, and in which order, the system uses the switches
  in the /etc/svc.conf file. The netdb.h header file defines the hostent
  structure.

  If using BIND, the information is obtained from a name server specified in
  the /etc/resolv.conf file.

  If the name parameter does not contain a dot "." and you are using BIND,
  the gethostbyname() function checks whether the environment variable
  HOSTALIASES is set. If set, it first searches the file named by HOSTALIASES
  for an alias matching the name parameter. The alias file has the following
  format:

       name1 name2

  name1	    The alias name. This name cannot include dots.

  name2	    The host name used by BIND to look up the host information. The
	    hosts database must be distributed by BIND.

NOTES
  The gethostbyname() function returns a pointer to thread-specific data.
  Subsequent calls to this or a related function from the same thread
  overwrite this data.

  [Digital]  The gethostbyname_r() function is an obsolete reentrant version
  of the gethostbyname() function.  It is supported in order to maintain
  backward compatibility with previous versions of the operating system and
  should not be used in new designs.  Note that you must zero-fill the hdptr
  structure before its first access by the gethostbyname_r() function.

RETURN VALUES
  Upon successful completion, the gethostbyname() function returns a pointer
  to a hostent structure.  If it reaches the end of the network hostname
  database, it returns a null pointer.

  [Digital]  Upon successful completion, the gethostbyname_r() function
  stores the hostent structure in the location pointed to by hptr, and
  returns a value of 0 (zero).	Upon failure, it returns a value of -1.

ERRORS
  If the gethostbyname() or gethostbyname_r() function call fails,  h_errno
  is set to one of the following the values:

  [HOST_NOT_FOUND]
	    The name you have used is not an official hostname or alias; this
	    is not a soft error, another type of name server request may be
	    successful.

  [NO_ADDRESS]
	    The requested name is valid but does not have an Internet address
	    at the name server.

  [NO_RECOVERY]
	    This is a nonrecoverable error.

  [TRY_AGAIN]
	    This is a soft error that indicates that the local server did not
	    receive a response from an authoritative server. A retry at some
	    later time may be successful.

  [Digital]  If any of the following conditions occurs, the gethostbyaddr_r()
  function sets errno to the corresponding value:

  [EINVAL]  The name, hptr, or hdptr is invalid.

FILES
  /etc/hosts
	    The DARPA Internet network hostname database. Each record in the
	    file occupies a single line and has three fields consisting of
	    the host address, official hostname, and aliases.

  /etc/resolv.conf
	    The resolver configuration file.

  /etc/svc.conf
	    The database service selection configuration file.

RELATED INFORMATION
  Functions: endhostent(3), gethostbyaddr(3), sethostent(3)

  Files: hostname(5), resolv.conf(4), svc.conf(4)

  Networks: bind_intro(7), nis_intro(7)

  Standards: standards(5)