Iterated hash
I feel like I'm missing something obvious.. 
I'm attempting to crack an iterated sha256($salt.$pass) hash, with a known salt. easy, if not for the iterated bit, but hashcat mentions format -m 1420 as "Raw Hash, Salted and / or Iterated", but I have no idea how to trigger this.

The hash is from the default implementation of Apache Shiro Hashing Service, which I'm auditing.

How do you make Hashcat run Iterated ?
You can't, because iteration (as well as salted) are somehow too unprecise to map it to code. Therefore, there can't be any generic hash-mode for this.

This is the way to go for you: