strange behaviour in ping when specifying timeout in msec

strange behaviour in ping when specifying timeout in msec

[Michele BOLOGNA]

Dear Mr. Yoshifuji,
I recently noticed a strange behaviour in ping from iputils.

First of all some information:
mbologna@neptune:~$ ping -V
ping utility, iputils-sss20071127

Now, I want to specify a timeout and after it expires I would like
that ping exits, regardless of the packets received, so I use the -W
option:

      -W timeout
              Time to wait for a response, in seconds. The option affects only
              timeout in absense of any responses, otherwise  ping  waits  for
              two RTTs.

So, if I decide to wait 1s for 5 packets, the ping works fine and
exits after 5s:

mbologna@neptune:~$ ping -c 5 -W 1 1.1.1.1
PING 1.1.1.1 (1.1.1.1) 56(84) bytes of data.

--- 1.1.1.1 ping statistics ---
5 packets transmitted, 0 received, 100% packet loss, time 3999ms

However, if I want to specify a timeout that is less than 1s, the ping
does not exit after 5*0.5 s and keeps staying active (notice the ^C):

mbologna@neptune:~$ ping -c 5 -W 0.5 1.1.1.1
PING 1.1.1.1 (1.1.1.1) 56(84) bytes of data.
^C
--- 1.1.1.1 ping statistics ---
5 packets transmitted, 0 received, 100% packet loss, time 3999ms

I also tried escaping the timeout with \ '' "" and so on, with no luck.
In a few words, is possible to specify a timeout that is less than 1 s?
Where am I wrong?

Thank you very much for your answer.
Best regards,
  Michele Bologna

-- 
Michele BOLOGNA
Email/GTalk: michele.bologna@gmail.com
Skype: michele-mb
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Web: www.mb.netsons.org

Re: strange behaviour in ping when specifying timeout in msec

[Brent Cook]

On Wednesday 05 August 2009 06:27:14 pm Michele BOLOGNA wrote:
> Dear Mr. Yoshifuji,
> I recently noticed a strange behaviour in ping from iputils.
>
> First of all some information:
> mbologna@neptune:~$ ping -V
> ping utility, iputils-sss20071127
>
> Now, I want to specify a timeout and after it expires I would like
> that ping exits, regardless of the packets received, so I use the -W
> option:
>
>       -W timeout
>               Time to wait for a response, in seconds. The option affects
> only timeout in absense of any responses, otherwise  ping  waits  for two
> RTTs.

If you check out the source to ping, you will see that the results of non-
integer arguments to -W is undefined, since atoi cannot detect errors. In your 
case, its probably being interpreted as 0. You can enter almost any value for 
-W without it showing an error, e.g. 'cat' or 'dog'.

    case 'W':
        lingertime = atoi(optarg);
        if (lingertime < 0 || lingertime > INT_MAX/1000000) {
            fprintf(stderr, "ping: bad linger time.\n");
            exit(2);
        }
        lingertime *= 1000;
        break;

Your best bet is perhaps to modify ping to parse time using strtof perhaps.

 - Brent