There are two ways to do this, depending on your device's partition layout.
Method A: Booting temporarily (Safest for testing) This boots the recovery image without permanently writing it to the phone's memory.
fastboot boot recovery.img
Your device should now reboot into the crDroid recovery mode. crdroid recoveryimg install
Method B: Flashing permanently (Standard method) This writes the recovery to the recovery partition.
fastboot flash recovery recovery.img
Once finished, use the hardware buttons (Volume keys) to select "Recovery Mode" and press Power to enter it. There are two ways to do this, depending
Cause: crDroid recovery expects signed builds.
Fix: Unless you are a developer, do not toggle signature verification. If you get this error with an official crDroid build, re-download the ZIP (corrupted download). You can try ADB sideload with adb -d sideload filename.zip.
Cause: Outdated Platform Tools or wrong syntax.
Fix: Update to the latest Platform Tools. Try fastboot flash recovery_a recovery.img or fastboot flash recovery_b recovery.img for A/B devices. Your device should now reboot into the crDroid recovery mode
If you see the crDroid logo or the TWRP splash screen, congratulations! You have successfully installed the custom recovery.
From here, you can:
Now that you have completed the "crdroid recoveryimg install" process, you need to actually install the operating system.