Guide_3DS/_pages/zh_TW/include/exploit-usm.txt

In this section, you will enter Safe Mode (a feature available on all 3DS family consoles) and navigate to a menu where unSAFE_MODE will be triggered, which will launch you into the boot9strap (custom firmware) installer.

1. With your console still powered off, hold the following buttons: (Left Shoulder) + (Right Shoulder) + (D-Pad Up) + (A), and while holding these buttons together, power on your console
    + Keep holding the buttons until the console boots into Safe Mode (a "system update" menu)
1. Press "OK" to accept the update
    + There is no update. This is part of the exploit
1. Press "I accept" to accept the terms and conditions
1. The update will eventually fail, with the error code `003-1099`. This is intended behaviour
1. When asked "Would you like to configure Internet settings?", select "Yes"
1. On the following menu, navigate to `Connection 1` -> `Change Settings` -> `Next Page (right arrow)` -> `Proxy Settings` -> `Detailed Setup` ([image](/images/screenshots/usm/safemode_highlighted.png))
1. If the exploit was successful, your console will have booted into SafeB9SInstaller
    + If your console instead freezes on a white screen, hold the POWER button until it turns off, then retry this section
    + If your console instead freezes on a red screen, you are missing `usm.bin` from the root of your SD card
    + If you get a different error, [follow this troubleshooting guide](troubleshooting#installing-boot9strap-usm)