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{{hatnote|This article is only for information and general usage on ntrboot. For detailed information on how to install [[3DS:boot9strap|boot9strap]] with this exploit, see [[3dsguide:ntrboot|our custom firmware installation guide's page.]]}}
ntrboot is a hardware exploit for the 3DS that relies on a DS [[3DS:Flashcarts|flashcart]] with the ntrboot exploit installed to boot a <code>.firm</code> payload from its attached SD. It is compatible with all console types & system versions and has very few requirements, thus making it an option for cases where multiple parts of your system such as shoulder buttons, DSiWare Management, or DS mode are broken or you need to recover from a brick.

==Requirements==
To use ntrboot, you need a DS flashcart compatible with the ntrboot exploit (see a full list of such carts [[3dsguide:ntrboot|here]]), a small magnet for all models except the old 2DS, and working {{B|Start}}, {{B|Select}}, and {{B|X}} buttons. You will require access to one of three things to install ntrboot: 
# A DSi or 3DS with a system version within the flashcart's supported range
# A DS/DS Lite
# A second 3DS with boot9strap already installed
If you do not have one of these, you must either buy a pre-flashed cart or [[3dsguide:index|install CFW to your device]] through another method first.

==How it Works==
{{ambox|text=Someone with more technical knowledge about ntrboot would be appreciated, as there are likely significant gaps here.}}
If you hold the keycombo {{B|Start}}, {{B|Select}}, and {{B|X}}, then press {{B|POWER}} while continuing to hold the other three buttons, the 3DS attempts to directly boot from a DS cartridge inserted in Slot-1. This will not work for regular DS cartridges, but if a flashcart that appears to be running official 3DS software is used, it loads the flashcart's software directly, which bypasses the normal boot process entirely.<br> 
In this case, ntrboot looks for a payload on the flashcart's SD root named <code>boot.firm</code>; if present, it immediately boots the system into it.<br>
This can be used with any <code>.firm</code> payload, which is also how boot9strap is installed via our guide.

==Potential Uses==
{{ambox|text=It seems like this should be rewritten so it can be moved into a subpage with instructions added. Also, there's likely more usages than this that should be listed.}}
ntrboot can be used for several purposes where normal methods would fail - it is a powerful tool capable of repairing nearly all software damage done to the console, as you have full control over all files on the system.<br>
If you are a power user, then the most practical firm payload to first boot an ntrboot flashcart with is <code>GodMode9.firm</code>, as it provides a very large amount of functionality and can chainload any other .firm as needed.
===Reinstalling the bootloader===
{{info|text=Make sure you install a valid <code>.firm</code>payload when doing this - since ntrboot only needs itself to boot you can retry near-infinitely, but it will take additional time to fix if done wrong.}}
If you have a payload as your bootloader that cannot boot to the rest of the system, you can run [[3DS:GodMode9|GodMode9]], <code>SafeB9SInstaller.firm</code>, or <code>OpenFirmInstaller.firm</code> via ntrboot to install either boot9strap or [[3DS:fastboot3DS|fastboot3DS]] in its place.
===Recovering from bricks===
If your console has been [[Brick|bricked]] due to custom firmware uninstall issues, a deleted/corrupted/altered NAND, or corrupted FIRM0/1 partitions, then ntrboot allows you to recover the system by loading GodMode9. From there, you can restore a NAND backup, perform a CTRTransfer or Lazarus3DS, or use other tools depending on the exact issue.
===Installing CFW in edge cases===
If your system cannot use seedminer or is a CHN region console, ntrboot is capable of installing CFW by loading <code>SafeB9SInstaller.firm</code>.

==Limitations==
{{ambox|text=Double-check this closely - the information here isn't certain to be entirely true, as it's made of memory-altered facts meshed with scattered trivia from various sources.}}
===Flashcart compatibility===
Not all flashcarts are compatible with the ntrboot exploit - for R4 cards, only cartridges produced between 2014 and 2020 are compatible, and others may be clones, counterfeits, or custom-made ones that either are bricked from flashing ntrboot or cannot safely uninstall it.
{{ambox|text=TODO: Explain why, in a technical sense, incompatible flashcarts are incompatible.}}

===Issues ntrboot cannot solve===
ntrboot is not capable of fixing hardware issues, and also cannot fix an issue relating to MCU_FIRM or a locked NAND. However, the latter two issues are nearly non-existent by this point, so this is not a limitation in practice.

===Normal flashcart usage with ntrboot installed===
Almost all flashcarts lose the ability to load <code>.nds</code> files with the ntrboot exploit installed, as the change in software means they no longer spoof an official game's data and thus consoles will either not detect them properly or refuse to load them.<br> 
Even the sole exceptions, the Acekard 2i and any potential carts with its kernel, can only use their regular functionality on a modded 3DS or DSi when ntrboot is installed due to Nintendo blocking access to those cards on the 3DS.
This issue can be fixed by reflashing the original kernel for the card, but this trades ntrboot access for the regular functionality.

===Dev consoles===
The normal guide for ntrboot does not work on developer consoles, and a specialized guide is required to install CFW for them - such a guide existed at [[https://panda.hacks.guide panda.hacks.guide]], but has since been closed off due to knowledge about dev consoles being limited to a very small number of people and thus, presumably, changes being hard to keep up with.