Requirements to maintain GC and apply for citizenship

[Manny17]

My parents got GC approved on Apr 15. They
intend to apply for citizenship when they become
eligible. They would like to go back and forth
between India and US.

Whats the requirement to maintain GC status
and to be eligible for citizenship? Are they
required to stay 2.5 yrs here at a strech or can
they spend 6 mons here, 6 mons in India?
I have heard they could take reentry permit and
stay outside for upto 2 yrs. Anyone know how
this works?

 

[annet]

They have to stay here at least 6 months
each year to convince the immigration
officer that they really consider US
their perminant residency.

If they don't want to do that, they can
apply for reentry permit (I-131, same
form for advace parole). They can
live in India more than 6 months. However
this is only valid for 2 years. It can
be renewed, but it will impact their
natualization since again the officer
will question whether you really need
the GC or not.

P.S. may I know when your parents did
the finder print?