CPAN (Net::FTP) for Perl Hangs on Cygwin

CPAN is an essential tool for Perl developers.  With the “cpan” command, you can install whole Perl libraries effortlessly.  However, on many default installations of cygwin, cpan simply hangs:

cpan> install LWP
CPAN: Storable loaded ok
Going to read /root/.cpan/Metadata
Database was generated on Sat, 26 Feb 2005 19:48:34 GMT
LWP not available
LWP not available
CPAN: Net::FTP loaded ok
Fetching with Net::FTP:…01mailrc.txt.gz

As it turns out, Net::FTP defaults to non-passive FTP, which conflicts with many firewalls since it requires a connection from the FTP server back to the FTP client.

How can you fix this?  Set the FTP_PASSIVE environment variable to 1:

BASH>  export FTP_PASSIVE=1 

This allows cpan to successfully retrieve files.

If you are creating a Net::FTP object in Perl, you can use:

$ftp=Net::FTP->new(HOST,[your options,]Passive   => ‘1’)

This will force the FTP connection to be passive and work through firewalls.

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