[erlang-questions] reliably figure out hostname

[JD Bothma]

I remember having to add something to the hosts file of a recent
ubuntu release before erlang would find out its own hostname properly.
Not sure if that's related. I'll see if I can dig up more info.

Does a machine necessarily have a FQDN? Is this necessarily exactly
one? Perhaps you'll have to work out what erlang does to get some
hostname and then set the appropriate setting (once) on each relevant
machine to make sure it gets what you expect it to.

JD

On 2 August 2012 18:33, Tim Watson <watson.timothy@REDACTED> wrote:
> On 2 August 2012 15:31, Raimo Niskanen
> <raimo+erlang-questions@REDACTED> wrote:
>> On Thu, Aug 02, 2012 at 09:40:03AM +0100, Gustav Simonsson wrote:
>>>
>>> {ok, LocalHostName} = inet:gethostname().
>>> inet_res:gethostbyname(LocalHostName).
>>
>> That forces using the OTP DNS resolver, which may be in conflict
>> with the current node configuration. The first approach should be:
>>
>>     {ok, LocalHostName} = inet:gethostname().
>>     inet:gethostbyname(LocalHostName).
>>
>
> That's clearly not what net_kernel is doing though:
>
> ==============================================
>
> t4@REDACTED:x-test $ erl -name foobar
> Erlang R15B01 (erts-5.9.1) [source] [64-bit] [smp:4:4]
> [async-threads:0] [hipe] [kernel-poll:false]
>
> Eshell V5.9.1  (abort with ^G)
> (foobar@REDACTED)1>
> BREAK: (a)bort (c)ontinue (p)roc info (i)nfo (l)oaded
>        (v)ersion (k)ill (D)b-tables (d)istribution
> a
> t4@REDACTED:x-test $ erl -name foobar@REDACTED
> Erlang R15B01 (erts-5.9.1) [source] [64-bit] [smp:4:4]
> [async-threads:0] [hipe] [kernel-poll:false]
>
> Eshell V5.9.1  (abort with ^G)
> (foobar@REDACTED)1>
> BREAK: (a)bort (c)ontinue (p)roc info (i)nfo (l)oaded
>        (v)ersion (k)ill (D)b-tables (d)istribution
> a
> t4@REDACTED:x-test $ erl
> Erlang R15B01 (erts-5.9.1) [source] [64-bit] [smp:4:4]
> [async-threads:0] [hipe] [kernel-poll:false]
>
> Eshell V5.9.1  (abort with ^G)
> 1> {ok, Host} = inet:gethostname().
> {ok,"frigg"}
> 2> inet:gethostbyname(Host).
> {ok,{hostent,"frigg",[],inet,4,[{127,0,0,1}]}}
> 3>
> BREAK: (a)bort (c)ontinue (p)roc info (i)nfo (l)oaded
>        (v)ersion (k)ill (D)b-tables (d)istribution
> a
> t4@REDACTED:x-test $
>
> ==============================================
>
> And the problem I've got is that whilst on this machine (CentOS 6.2,
> R15B01-64bit) the network configuration is *somehow* set up so that
> net_kernal magically picks up the right domain info, this doesn't work
> consistently everywhere else. And neither does calling inet_rc, as
> Gustav suggested:
>
> ==============================================
> t4@REDACTED:x-test $ erl
> Erlang R15B01 (erts-5.9.1) [source] [64-bit] [smp:4:4]
> [async-threads:0] [hipe] [kernel-poll:false]
>
> Eshell V5.9.1  (abort with ^G)
> 1> {ok, LocalHostName} = inet:gethostname().
> {ok,"frigg"}
> 2> inet_res:gethostbyname(LocalHostName).
> {error,nxdomain}
> 3>
>
> =============================================
>
> On some other machines, inet_res:gethostbyname/1 returns {error, timeout}.
>
>> / Raimo Niskanen
>>
>>>
>>> You get a hostent record back which has the FQDN.
>>>
>>> // Gustav Simonsson
>>>
>>> Sent from my PC
>>>
>>> ----- Original Message -----
>>> > From: "Tim Watson" <watson.timothy@REDACTED>
>>> > To: "Tim Watson" <watson.timothy@REDACTED>
>>> > Cc: "erlang-questions Questions" <erlang-questions@REDACTED>
>>> > Sent: Thursday, 2 August, 2012 10:17:32 AM
>>> > Subject: Re: [erlang-questions] reliably figure out hostname
>>> >
>>> >
>>> >
>>> > Any takers for this? I can't be the only person who's had to figure
>>> > this out. The context is a distributed systems testing framework
>>> > that needs to support resolving 'localhost' to a proper host name so
>>> > the framework can become a hidden node and interact with the other
>>> > erlang nodes It is testing against. Having to specify the real host
>>> > name would make configuring the tool across different machines and
>>> > development environments unpleasantly complicated so figuring out
>>> > the right hostname is a boon in terms of keeping the configuration
>>> > overhead down, but doing this for long names nodes is proving highly
>>> > awkward.
>>> >
>>> >
>>> > Can anyone suggest a good portable solution?
>>> >
>>> > On 31 Jul 2012, at 13:43, Tim Watson < watson.timothy@REDACTED >
>>> > wrote:
>>> >
>>> >
>>> >
>>> >
>>> >
>>> > Is there a way to calculate the hostname reliably across platforms in
>>> > Erlang? I have a non-distributed node that I wish to become a
>>> > distributed node. Normally I call net_kernel:start([Name,
>>> > shortnames]) and this is just fine. It also works with [Name,
>>> > longnames] *sometimes and on some systems* - but other times it
>>> > pukes. I've tried looking in the 'domain' or 'search' entries from
>>> > inet:get_rc/0 but these are not always populated, even when dns
>>> > config is clearly in place. I've also tried using
>>> > 'inet_db:get_searchlist/0' but again, sometimes this returns [[]]
>>> > but net_kernel:start([foobar, longnames]) doesn't work, whereas
>>> > doing net_kernel:start([ foobar@REDACTED , longnames]) does.
>>> >
>>> >
>>> > Am I missing something incredibly obvious here? *is* there actually a
>>> > simple way of determining what the proper fqdn for the machine
>>> > should be, without breaking out to the os? I had even considered
>>> > doing inet:gethostbyname/1 but again, the search domains entry seems
>>> > to be empty, so I'd assume that -name foobar will work whereas in
>>> > fact, -name foobar @fqdn is required otherwise net_kernel won't
>>> > start.
>>> > _______________________________________________
>>> > erlang-questions mailing list
>>> > erlang-questions@REDACTED
>>> > http://erlang.org/mailman/listinfo/erlang-questions
>>> >
>>> _______________________________________________
>>> erlang-questions mailing list
>>> erlang-questions@REDACTED
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>>
>> --
>>
>> / Raimo Niskanen, Erlang/OTP, Ericsson AB
>> _______________________________________________
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