#3 <nmap-err>Warning: Hostname localhost resolves to 2 IPs. Using 127.0.0.1.

[Tomas Plesnik]

Hi Max,

I found a problem when I tryed to install Nmap::Scanner (via cpan) on our Debian server (3.2.0-4-amd64 #1 SMP Debian 3.2.60-1+deb7u3 x86_64 GNU/Linux) with enabled IPv6 networking. The tests were failed:

cpan[1]> install Nmap::Scanner
Reading '/root/.cpan/Metadata'
  Database was generated on Sun, 05 Oct 2014 11:41:02 GMT
Running install for module 'Nmap::Scanner'
Checksum for /root/.cpan/sources/authors/id/M/MA/MAXSCHUBE/Nmap-Scanner-1.0.tar.gz ok
Scanning cache /root/.cpan/build for sizes
............................................................................DONE
Configuring M/MA/MAXSCHUBE/Nmap-Scanner-1.0.tar.gz with Makefile.PL
Checking if your kit is complete...
Looks good
Generating a Unix-style Makefile
Writing Makefile for Nmap::Scanner
Writing MYMETA.yml and MYMETA.json
  MAXSCHUBE/Nmap-Scanner-1.0.tar.gz
  /usr/bin/perl Makefile.PL INSTALLDIRS=site -- OK
Running make for M/MA/MAXSCHUBE/Nmap-Scanner-1.0.tar.gz
cp lib/Nmap/Scanner/Service.pm blib/lib/Nmap/Scanner/Service.pm
cp lib/Nmap/Scanner/OS/PortUsed.pm blib/lib/Nmap/Scanner/OS/PortUsed.pm
cp lib/Nmap/Scanner/OS/Uptime.pm blib/lib/Nmap/Scanner/OS/Uptime.pm
cp lib/Nmap/Scanner/OS/TCPSequence.pm blib/lib/Nmap/Scanner/OS/TCPSequence.pm
cp lib/Nmap/Scanner/TaskProgress.pm blib/lib/Nmap/Scanner/TaskProgress.pm
cp lib/Nmap/Scanner/Backend.pm blib/lib/Nmap/Scanner/Backend.pm
cp lib/Nmap/Scanner/Util.pm blib/lib/Nmap/Scanner/Util.pm
cp lib/Nmap/Scanner/Backend/Processor.pm blib/lib/Nmap/Scanner/Backend/Processor.pm
cp lib/Nmap/Scanner/Port.pm blib/lib/Nmap/Scanner/Port.pm
cp lib/Nmap/Scanner/Distance.pm blib/lib/Nmap/Scanner/Distance.pm
cp lib/Nmap/Scanner/Hosts.pm blib/lib/Nmap/Scanner/Hosts.pm
cp lib/Nmap/Scanner/PortList.pm blib/lib/Nmap/Scanner/PortList.pm
cp lib/Nmap/Scanner/ScanInfo.pm blib/lib/Nmap/Scanner/ScanInfo.pm
cp lib/Nmap/Scanner/NmapRun.pm blib/lib/Nmap/Scanner/NmapRun.pm
cp lib/Nmap/Scanner/OS.pm blib/lib/Nmap/Scanner/OS.pm
cp lib/Nmap/Scanner/Host.pm blib/lib/Nmap/Scanner/Host.pm
cp lib/Nmap/Scanner/ExtraPorts.pm blib/lib/Nmap/Scanner/ExtraPorts.pm
cp lib/Nmap/Scanner/OS/Class.pm blib/lib/Nmap/Scanner/OS/Class.pm
cp lib/Nmap/Scanner/Hostname.pm blib/lib/Nmap/Scanner/Hostname.pm
cp lib/Nmap/Scanner/Scanner.pm blib/lib/Nmap/Scanner/Scanner.pm
cp lib/Nmap/Scanner/Task.pm blib/lib/Nmap/Scanner/Task.pm
cp lib/Nmap/Scanner/HostList.pm blib/lib/Nmap/Scanner/HostList.pm
cp lib/Nmap/Scanner/OS/Fingerprint.pm blib/lib/Nmap/Scanner/OS/Fingerprint.pm
cp lib/Nmap/Scanner/RunStats.pm blib/lib/Nmap/Scanner/RunStats.pm
cp lib/Nmap/Scanner/Backend/Results.pm blib/lib/Nmap/Scanner/Backend/Results.pm
cp lib/Nmap/Scanner/Util/BannerScanner.pm blib/lib/Nmap/Scanner/Util/BannerScanner.pm
cp lib/Nmap/Scanner/OS/Match.pm blib/lib/Nmap/Scanner/OS/Match.pm
cp lib/Nmap/Scanner/Address.pm blib/lib/Nmap/Scanner/Address.pm
cp lib/Nmap/Scanner.pm blib/lib/Nmap/Scanner.pm
cp lib/Nmap/Scanner/OS/TCPTSSequence.pm blib/lib/Nmap/Scanner/OS/TCPTSSequence.pm
cp lib/Nmap/Scanner/RunStats/Finished.pm blib/lib/Nmap/Scanner/RunStats/Finished.pm
cp lib/Nmap/Scanner/Backend/XML.pm blib/lib/Nmap/Scanner/Backend/XML.pm
cp lib/Nmap/Scanner/OS/IPIdSequence.pm blib/lib/Nmap/Scanner/OS/IPIdSequence.pm
Manifying blib/man3/Nmap::Scanner.3pm
Manifying blib/man3/Nmap::Scanner::Address.3pm
Manifying blib/man3/Nmap::Scanner::Backend::Processor.3pm
Manifying blib/man3/Nmap::Scanner::Backend::Results.3pm
Manifying blib/man3/Nmap::Scanner::Distance.3pm
Manifying blib/man3/Nmap::Scanner::ExtraPorts.3pm
Manifying blib/man3/Nmap::Scanner::Host.3pm
Manifying blib/man3/Nmap::Scanner::HostList.3pm
Manifying blib/man3/Nmap::Scanner::Hostname.3pm
Manifying blib/man3/Nmap::Scanner::Hosts.3pm
Manifying blib/man3/Nmap::Scanner::NmapRun.3pm
Manifying blib/man3/Nmap::Scanner::OS.3pm
Manifying blib/man3/Nmap::Scanner::OS::Class.3pm
Manifying blib/man3/Nmap::Scanner::OS::Fingerprint.3pm
Manifying blib/man3/Nmap::Scanner::OS::IPIdSequence.3pm
Manifying blib/man3/Nmap::Scanner::OS::Match.3pm
Manifying blib/man3/Nmap::Scanner::OS::PortUsed.3pm
Manifying blib/man3/Nmap::Scanner::OS::TCPSequence.3pm
Manifying blib/man3/Nmap::Scanner::OS::TCPTSSequence.3pm
Manifying blib/man3/Nmap::Scanner::OS::Uptime.3pm
Manifying blib/man3/Nmap::Scanner::Port.3pm
Manifying blib/man3/Nmap::Scanner::PortList.3pm
Manifying blib/man3/Nmap::Scanner::RunStats.3pm
Manifying blib/man3/Nmap::Scanner::RunStats::Finished.3pm
Manifying blib/man3/Nmap::Scanner::ScanInfo.3pm
Manifying blib/man3/Nmap::Scanner::Scanner.3pm
Manifying blib/man3/Nmap::Scanner::Service.3pm
Manifying blib/man3/Nmap::Scanner::Task.3pm
Manifying blib/man3/Nmap::Scanner::TaskProgress.3pm
Manifying blib/man3/Nmap::Scanner::Util::BannerScanner.3pm
  MAXSCHUBE/Nmap-Scanner-1.0.tar.gz
  /usr/bin/make -- OK
Running make test
PERL_DL_NONLAZY=1 /usr/bin/perl "-MExtUtils::Command::MM" "-MTest::Harness" "-e" "undef *Test::Harness::Switches; test_harness(0, 'blib/lib', 'blib/arch')" t/*.t
t/batch_tcp_syn_scan.t ............ 1/3 <nmap-error>
  <pid="9659"/>
  <cmdline="'/usr/bin/nmap' -v -v -v -sT -p 1-1024 -oX - localhost"/>
  <nmap-err>Warning: Hostname localhost resolves to 2 IPs. Using 127.0.0.1.
</nmap-msg>
</nmap-error>
t/batch_tcp_syn_scan.t ............ Dubious, test returned 1 (wstat 256, 0x100)
Failed 2/3 subtests
t/event_tcp_syn_scan.t ............ 1/3 <nmap-error>
  <pid="9665"/>
  <cmdline="'/usr/bin/nmap' -v -v -v -sT -p 1-1024 -oX - localhost"/>
  <nmap-err>Warning: Hostname localhost resolves to 2 IPs. Using 127.0.0.1.
</nmap-msg>
</nmap-error>
t/event_tcp_syn_scan.t ............ Dubious, test returned 1 (wstat 256, 0x100)
Failed 2/3 subtests
t/event_tcp_syn_scan_from_file.t .. ok

Test Summary Report
-------------------
t/batch_tcp_syn_scan.t          (Wstat: 256 Tests: 1 Failed: 0)
  Non-zero exit status: 1
  Parse errors: Bad plan.  You planned 3 tests but ran 1.
t/event_tcp_syn_scan.t          (Wstat: 256 Tests: 1 Failed: 0)
  Non-zero exit status: 1
  Parse errors: Bad plan.  You planned 3 tests but ran 1.
Files=3, Tests=9,  1 wallclock secs ( 0.02 usr  0.01 sys +  0.52 cusr  0.06 csys =  0.61 CPU)
Result: FAIL
Failed 2/3 test programs. 0/9 subtests failed.
make: *** [test_dynamic] Error 255
  MAXSCHUBE/Nmap-Scanner-1.0.tar.gz
  /usr/bin/make test -- NOT OK
//hint// to see the cpan-testers results for installing this module, try:
  reports MAXSCHUBE/Nmap-Scanner-1.0.tar.gz
Failed during this command:
 MAXSCHUBE/Nmap-Scanner-1.0.tar.gz            : make_test NO

After a bit of googling I've found that the problem was in /etc/hosts where localhost has assigned two addresses 127.0.0.1 and ::1. When I deleted ::1 (IPv6 localhost address), all of tests successfully passed.

Best regards,

Tomas