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Re: Blocking DNS lookup on MC startup

Subject: Re: Blocking DNS lookup on MC startup
From:
Date: Tue, 30 May 2006 10:54:32 +0200
On Tue, May 30, 2006 at 10:42:39AM +0300, Pavel Tsekov wrote:
> Someone was complaining about the same issue recently. I think
> he/she was experiencing this long delay on a FreeBSD system. Can
> you give us more details about the system on which you run MC and
> see the long delay ? The output of "mc -V" would be usefull too.

The delay appears before any output generated by -V:

GNU Midnight Commander 4.6.1-pre3
Virtual File System: tarfs, extfs, cpiofs, ftpfs, fish, smbfs
With builtin Editor
Using included S-Lang library with terminfo database
With subshell support as default
With support for background operations
With mouse support on xterm and Linux console
With support for X11 events
With internationalization support
With multiple codepages support

Strace and a tcpdump show that MC is performing DNS requests, the 
long timeout is because DNS servers are unreachable.

The requests are for every network interface name, both lowercase 
and capitalized. On my test machine it tries to resolve:

   lo.
   LO.
   eth0.
   ETH0.
   eth1.
   ETH1.
   eth2.
   ETH2.

i.e. every network interface name (loopback and 3 Ethernet).
The DNS query in tcpdump looks like:

    IP 127.0.0.1.1074 > 127.0.0.1.53:  21938+ A? LO. (20)

The same delay is experienced if I execute

  nslookup lo.
  nslookup LO.
  ...

The question is: why MC is doing DNS queries? Is possible to 
disable them?

This is an strace snippet:

  connect(4, {sa_family=AF_INET, sin_port=htons(53), 
  sin_addr=inet_addr("217.19.150.6")}, 28) = 0
  send(4, "\272\347\1\0\0\1\0\0\0\0\0\0\4ETH0\0\0\1\0\1", 22, 0) 
      = 22
  gettimeofday({1148978445, 848460}, NULL) = 0


-- 
Niccolo Rigacci
Firenze - Italy

Iraq, missione di pace: 38059 morti - www.iraqbodycount.net
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