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

1. 将你的主机置于关机状态，按住 L + R + ↑ + A 四个按键，然后按下电源键
  + 按住这几个键，直到主机进入安全模式（一个“系统更新”菜单）
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 device will have booted into SafeB9SInstaller
  + If your device instead freezes on a white screen, hold the POWER button until it turns off, then retry this section
  + If your device 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)