A+ and Linux

I know that in the current A+ exams, linux isn't covered. Is there any kind of certification process for linux OS's? I'm working on my A+ cert now, but I was wondering if there is any thing I can do for linux to add that to the list of things I "know" other than just saying "I've been using linux for X number of years..."...

Any ideas?

Thanks

Comptia's Linux+ http://www.comptia.org/certification/linux/?nav=quick
Linux Profesional Instutes Certification http://www.lpi.org/
Redhat Cert https://www.redhat.com/training/certification/
SUSE Cert http://www.novell.com/training/certinfo/