How do I add a PTR record?

First, you'll want to make sure you've set up your domain zone already and that it is resolving to your IP.

After that:

1. Select your Linode
2. Go to the "Remote Access" tab
3. Click "Reverse DNS"
4. Enter your Linode’s fully qualified domain name in the Hostname field

From here, you'll just need to confirm that a match has been found for your address.

You can find additional details in the Reverse DNS Guide

With the new interface it seems to be on the networking tab - click the "…" to far the right of the ip address.

but how long does it take to propogate to the linode DNS servers?

@jasenbetts how long did it take for an rDNS change to become visible?

Yes @jasen you are correct, the Cloud Manager interface will be a different set of steps than what thorner has described, but the Reverse DNS Guide he linked to has the necessary instructions.

@chaetura, it should not take more than an hour for your rDNS changes to become visible.

Also consider checking the Linode guide to PTR records here for more info.