I am a green card holder and wish to travel to San Francisco to visit my son. Can I issue a one way ticket as I am not sure about my return date? Will I have a problem at the immigration counter in US? Please advise
As a US permanent resident (green card holder), there's no problem entering the US on a one way ticket. The idea of permanent residency is that you are allowed to live and work in the US permanently. As a permanent resident, the US is your home to return to, so there's no requirement that you have a return ticket.
There's a potential problem if you're not actually living in the US, and I can't tell from your question whether or not that's the case. It's possible to abandon permanent residency if you move to another country intending to live there permanently or are absent from the US for an extended period of time without obtaining a re-entry permit. If this is the case for you, you could be stopped at the border and have an immigration problem. You'd want to talk to an immigration lawyer if that's actually the case, and you want to maintain permanent residency.
If none of that applies, then there's no problem entering the US on a one way ticket as a permanent resident.
Note that a one-way ticket may wind up being more costly, so you'll need to compare airfares.
This question indicates that the immigration officer has access to your flight information.
As the cost of two single fares will often be much higher than a return fare plus the cost of a change I'd be more inclined to book a return and change the date if need be.
However I have no experience that having only a single flight would be a problem, especially for a green card holder.