Monday, May 12, 2008


Fixing Perl installation under Cygwin

I discussed on multiple occasions before various issues arising from Cygwin upgrade, but there is one problem I fixed multiple times but never cared to document properly.

Perl built-in extension installation tools rely on existence and/or executability of certain files; this is tested with Perl test operators like 'if -r <filename>". As specified in the documentation, this operator tests that "File is readable by effective uid/gid.". No doubt that this test simply matches file permissions as reported by 'stat'' system call with file owner and current user id.

This seems sane enough, but the trouble is, Windows-centric notions of "Administrative rights" cannot be reliably mapped to Cygwin world. I always work in Windows as "myself," but with full Administrative rights, but Cygwin cannot possibly appreciate that I can access each file as if I were "Administrator" even though I am not one. As a result, multiple files which are created with permissions like that:

-rwxrwx---+ 1 Administrators SYSTEM 470528 May  1  2007 /usr/bin/bash.exe*

fail Perl's "-r" test, unless of course one wants to actually login as "Administrator", though I can still read and execute them.

While it is beyond me why Cygwin should create such peculiar permissions, here is a quick patch which should resolve most, if not all, problems related to installing Perl extensions.

chmod a+x /usr/bin/perl.exe
cd /usr/lib/perl5/5.8/ExtUtils
chmod a+x,a+r typemap xsubpp .
cd /usr/lib/perl5/vendor_perl/5.8/ExtUtils
chmod a+x,a+r xsubpp .

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