Creating a subdomain that redirects to a URL?
I thought you did this with the CNAME?
The error I'm getting is: • You have entered an invalid target. It must be a valid hostname.
In the fields for the CNAME page I have
edit: I've also tried linkedin.url.com in the Hostname field as well. I guess I just don't understand how to make that a valid hostname?
Point the subdomain to your Linode. Have your webserver have a rewrite rule for linkedin.mydomainname.com (301 redirect) that points to your LinkedIn URL instead.
A CNAME is an alias not a redirect.