Can you install NiFi on Hortonworks HDP 2.6.1?
If so, can you direct me to installation steps?
You will need to install HDF Mpack on the HDP cluster which is managed by Ambari as mentioned in the following link:
You can get the HDF Management Pack archive based on your OS here: https://docs.hortonworks.com/HDPDocuments/HDF3/HDF-3.1.1/bk_release-notes/content/ch_hdf_relnotes.ht...
After installing the Mpack to your Ambari Managed HDP cluster when you will restart Ambari server then you should be able to see "NiFi" option when you will click on "Add Service" button.
assuming you are trying on sandbox. if yes download Hortonworks DataFlow (HDF) 3.1 on Hortonworks Sandbox rather 2.6.4