Instead of running the entire process as root, why don't you configure cpan to install as root using one of the following: 
o conf make_install_make_command    'su root -c make'
o conf mbuild_install_build_command 'su root -c ./Build'

[download]
o conf make_install_make_command    'sudo make'
o conf mbuild_install_build_command 'sudo ./Build'

[download]
o conf make_install_make_command    'sudo -u root make'
o conf mbuild_install_build_command 'sudo -u root ./Build'

[download]

It won't solve your problem so much as bypass it. And it's safer as a bonus!

Note that the change isn't permanent unless you follow up using the following: 

o conf commit

[download]

Update: Added instructions to use su/sudo with distros that use Module::Build (Build.PL).
Update: Fixed to use correct configuration option name, as per afauno's reply.

In reply to Re: Cannot install CPAN (or any other modules) as root user!!! by ikegami
in thread Cannot install CPAN (or any other modules) as root user!!! by ARiccela

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