If the system has been halted, or has panicked before boot, then it will be sat at the CFE or Loader prompt (depending on the hardware version). From here it’s pretty straight forward to get the system booting, although if it has panicked on boot, you’ll want to troubleshoot that first!
Whatever is the latest successful install of ONTAP will be booted into and whatever system volume is registered by the filer will be loaded. This will read the base install from the compact flash card before reading the configuration from disk and booting into this.
Is pretty much the same as “boot_ontap”. It will simply boot into the primary ONTAP version that is on the system.
The system should always have storage a second boot image. This may either be a backup of the primary boot image from the factory, or it will be the last version of ONTAP before an upgrade. If an upgrade has gone badly, use boot_secondary to get back to the old ONTAP and do a system revert (simply doing a snap restore of vol0 isn’t enough as the ONTAP needs to be committed onto the compact flash card). Checkout NetApp / IBM’s website for full details on how to do a system revert.
If you are having some hardware problems, or you need to diagnose an area of the system, you can use…
And so long as the compact flash card has this installed (they all should, but I have seen one without!), then you will boot into the diagnostics tools and you can run full system diags to determine any issues, or simply check everything is fine.