Max stay allowed for GC holders outside US

[tsrusa2002]

I am not clear about what is the max stay allowed for family based GC holders outside US. The rule book that came along with the GC says one year.
If we just want to keep GC active (don't plan to apply for citizenship), is it 6 months or we can stay outiside for more (like sometime 7-8 months) without requiring re-entry permit?

My parent would like to go every year..usually for 6 months but wanted to if more than that is permissible as long as it is less than 1 year.

[immihelp]

It is not simple as just 6 months or 1 year. You have to many other things to maintain your green card.

Read http://www.immihelp.com/greencard/retain-greencard.html

[neer_chat]

Last I knew that within 6 month you need to visit America and prove your ties with America to maintain Green Card. However I have recently heard from my friends that now USCIS as reduced that restriction from 6 months to 2 months. So if you are going out of USA for more than 2 months then you need to take pre-permission from USCIS. Else you re-entry will be denied.

Any ideas on that?