I have tested using an extremely minimal PXELinux menu. Even with no arguments, the same error appears. I have verified that the initrd and kernel files exist.
The issue appeared to be with the OS install media.
The kernel and initrd does not exist in the TFTP folder, below is what is present in their place.
<!DOCTYPE HTML PUBLIC "-//IETF//DTD HTML 2.0//EN">
<html><head>
<title>404 Not Found</title>
</head><body>
<h1>Not Found</h1>
<p>The requested URL was not found on this server.</p>
</body></html>
Known bug, Ubuntu no longer ships kernel(initramdisk) in their repos. They confirmed to fix this in the future release, it will be the new installer tho so some changes in Foreman will be required.
We caught up on our Foreman upgrades and just ran to this. We noticed that we had older initrd & vmlinuz files, and they were all the same size.
We copied the good files over the bad files and then changed the permissions of the files so that Foreman couldn’t overwrite them again, and now the installer seems to work.
This lengthy thread discusses how and why Canonical stopped publishing the netboot files for Ubuntu. Some folks are rather frustrated that Canonical stopped supporting a traditional netboot for server installs.