gethostbyname(3N) gethostbyname(3N)
gethostbyname, gethostbyname_r, gethostbyaddr, gethostbyaddr_r,
gethostent, gethostent_r, fgethostent, fgethostent_r, sethostent,
endhostent, herror, hstrerror - get network host entry
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <netdb.h>
extern int h_errno;
struct hostent *gethostbyname(const char *name);
struct hostent *gethostbyname_r(const char *name, struct hostent *hent, char *buffer, int bufsize, int *h_errnop);
struct hostent *gethostbyaddr(const void *addr, size_t addrlen, int type);
struct hostent *gethostbyaddr_r(const void *addr, size_t addrlen, int type, struct hostent *hent, char *buffer, int bufsize, int *h_errnop);
struct hostent *gethostent(void);
struct hostent *gethostent_r(struct hostent *hent, char buffer, int bufsize);
struct hostent *fgethostent(FILE *f);
struct hostent *fgethostent_r(FILE *f, struct hostent *hent, char buffer, int bufsize);
void sethostent(int stayopen);
void endhostent(void);
void herror(const char *string);
char *hstrerror(int err);
gethostbyname, gethostbyaddr and their reentrant counterpoints each
return a pointer to a hostent data structure describing an Internet host
referenced by name or by address, respectively. This structure contains
either the information obtained from broken-out fields from a line in
/etc/hosts. or some other back-end hosts database.
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
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gethostbyname(3N) gethostbyname(3N)
compatibility */
The members of this structure are:
h_name Official name of the host.
h_aliases A zero terminated array of alternate names for the host.
h_addrtype The type of address being returned; currently always
AF_INET.
h_length The length, in bytes, of the address.
h_addr_list A zero terminated array of network addresses for the host.
Host addresses are returned in network byte order.
h_addr The first address in h_addr_list; this is for backward
compatibility.
The name argument to gethostbyname is a character string containing an
Internet hostname or an Internet address in standard dot notation (see
inet(3N)). If the name contains no dot, and if the environment variable
HOSTALIASES contains the name of an alias file, the alias file is first
searched for an alias matching the input name. See hostname(5) for the
alias file format. The addr argument to gethostbyaddr points to a buffer
containing a 32-bit Internet host address in network byte order. addrlen
contains the address length in bytes; it should be set to sizeof(struct
in_addr). type specifies the address family and should be set to
AF_INET.
The gethostbyname and gethostbyaddr routines only parse /etc/hosts format
configuration files. An external data supplier nsd(1M) may be used to
provide data from another source such as the Domain Name Service daemon
named, or the NIS databases.
An administrator may specify a default ordering of the services in the
nsd configuration file /etc/nsswitch.conf.
When using the Domain Name Server, gethostbyname searches for the named
host in the current domain and its parents unless the name ends in a dot.
See hostname(5) for the domain search procedure. Also when using the
name server, gethostbyname restricts the length of each subdomain name in
a hostname to at most 63 characters.
When nsd is running, gethostent obtains the next entry in the
hosts.byaddr table. sethostent and endhostent reset the pointer into the
map to the beginning.
If nsd is not running, gethostent reads the next line of /etc/hosts,
opening the file if necessary. sethostent opens and rewinds the file.
If the stayopen flag is non-zero, the file is not closed after each call
to gethostbynameorgethostbyaddr. endhostent closes the file.
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gethostbyname(3N) gethostbyname(3N)
The routines fgethostent and fgethostent_r will return the next line from
the supplied file broken out into a hostent structure. This file must be
of the same format as /etc/hosts .
The routines gethostbyname, gethostbyaddr, gethostent, and fgethostent
all return pointers to data in a static space. Reentrant versions of
each of these are supplied as gethostbyname_r, gethostbyaddr_r,
gethostent_r and fgethostent_r. These routines parse the results into
passed in space. They each have extra arguments for an address to a
struct hostent structure and a flat buffer.
Error return status from gethostbyname and gethostbyaddr is indicated by
return of a null (0) pointer. The global integer h_errno can then be
checked to see whether this is a temporary failure or an invalid or
unknown host. The routine herror can be used to print an error message
to file descriptor 2 (standard error) describing the failure. If its
argument string is non-NULL, it is printed, followed by a colon and a
space. The error message is printed with a trailing newline. To
simplify variant formatting of messages, hstrerror takes an error number
(typically h_errno) and returns the corresponding message string.
h_errno can have the following values:
HOST_NOT_FOUND No such host is known.
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.
NO_RECOVERY Some unexpected server failure was encountered. This is
a non-recoverable error.
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 results
in an answer; for example, a mail-forwarder can be
registered for this domain.
The Mips ABI specifies nothing but local files so applications which wish
to use anything else must compile with libc prior to libnsl in the
library list.
When nsd is running changes to the local host file may not be noticed by
gethostent() until the enumeration cache file has timed out.
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gethostbyname(3N) gethostbyname(3N)
/etc/hosts /etc/nsswitch.conf
/etc/resolv.conf contains addresses of remote name servers
HOSTALIASES contains hostname aliases
named(1M), nsd(1N), gethostent(3N), resolver(3N), hosts(4), resolver(4),
hostname(5).
IRIX Network Programming Guide
IRIX Admin: Networking and Mail
Only the Internet address format is currently understood.
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