Re: WARNING : libc6 Version: 2.0.7t-1 breaks resolv routines
Michael Stone wrote:
>
> That is the correct behavior. The host program only queries DNS servers;
> it does not consult the local host table. You can try pinging a hostname
> in the host table to see if it resolves.
>
Well let's try to close this issue once for all to everybody's relief.
First of all I would like to apologize for having flooded the group with
something
that appears to be a non problem to most of us.
The doubt has arisen since contrary to what the man page and your append
states,
host has a mixed behaviour which IMHO is not very clean.
If you do a "strace 127.0.0.1" you will see that the host command
command used in this way WILL take a look to your /etc/nsswitch.conf
file and if the latter has a hosts: files,dns line in it, will open your
/etc/hosts file, read from it and retrieve the corresponding name
WITHOUT EVER going to a DNS (can check also with IPTRAF or TCPDUMP if
you are an overly suspicious character 8->).
Conversely if you do a "strace localhost" with the same situation host
will totally ignore /etc/nsswitch and as you and the man page state,
attempt a DNS query.
This mixed behavior of the host command I discovered makes it an
unreliable debugging to tool.
If I need to debug DNS I will ONLY use dig or nslookup from now on.
If I want to exercise the way my system uses the gethostby*() routines
(which are
used by many programs), I have compiled a program built for that by a
friend of mine (address.c) which will behave CORRECTLY according to what
the /etc/nsswitch says ...
This is the behavior I would have expected from "host" ...
Case closed.
Thank you to everyone for getting me to understand Unix a bit better 8->
PS The reason for which I like Unix against non-oss like Win95/WinNT is
that
with sufficient knowledge and sweat you can always understand why
Unix
behaves in a certain way .. I hate non deterministic looking OSs ...
PPS I cannot check now but I would bet fiver that AIX host commands
behaves
like I think it should ...
---
Robert J. Alexander <rja@raleigh.ibm.com>
AIX Certified System Administrator - Debian Linux addict - Win.\* victim
Via Sciangai, 53 - 00144 Rome, Italy#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <sys/types.h>
#include <unistd.h>
#include <netdb.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
/*
Simple little program to exercise name resolution via gethostby*()
routines.
Usage:
addressof hostname|ipaddress
schales, August 1998 - IBM
used as a better "host" command. Will honour /etc/nsswitch.conf
and read from /etc/hosts when needed.
*/
static int resolve(char *);
int
main(int argc, char **argv)
{
int rc, i;
rc = EXIT_SUCCESS;
if(argc != 1){
for(i=1;i<argc;i++){
if(resolve(argv[i]) != 0)
rc = EXIT_FAILURE;
}
}
else {
fprintf(stderr, "Usage: %s hostspec [hostspec [hostspec...]]\n",
argv[0]);
fputs("\n\twhere `hostspec' is either a hostname or an IPv4 address.\n\n",
stderr);
}
return rc;
}
static int
resolve(char *hostspec)
{
struct hostent *he;
unsigned long addr;
int i;
if((addr = inet_addr(hostspec)) != (unsigned long)-1)
he = gethostbyaddr((char *)&addr, 4, AF_INET);
else
he = gethostbyname(hostspec);
if(!he){
printf("%s: No information.\n", hostspec);
return -1;
}
printf("Name: %s\n", he->h_name);
if(he->h_aliases[0]){
if(he->h_addr_list[1]){
puts("Aliases:");
for(i=0;he->h_aliases[i];i++)
printf("\t%s\n", he->h_aliases[i]);
}
else {
printf("Alias: %s\n", he->h_aliases[0]);
}
}
if(he->h_addr_list[0]){
struct in_addr ia;
if(he->h_addr_list[1]){
puts("Addresses:");
for(i=0;he->h_addr_list[i];i++){
memcpy((void *)&ia.s_addr, he->h_addr_list[i], 4);
printf("\t%s\n", inet_ntoa(ia));
}
}
else {
memcpy((void *)&ia.s_addr, he->h_addr_list[0], 4);
printf("Address: %s\n", inet_ntoa(ia));
}
}
else {
puts("No address records found.");
}
return 0;
}
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