Story

I like scrcpy. It allows me to cast my phone to computer and use it ther thanks to cable technology (wifi works too). So, after hopping to Pop_OS! I reinstalled adb and scrcpy. But this time scrcpy didn't work. Instead it throw this error:

adb: error: failed to get feature set: device unauthorized.
This adb server's $ADB_VENDOR_KEYS is not set
Try 'adb kill-server' if that seems wrong.
Otherwise check for a confirmation dialog on your device.
ERROR: "adb push" returned with value 1

Easy way | Grant access using prompt on the phone

After enabling USB debugging in Developer options connect phone to computer and run scrcpy. Phone should prompt you for granting access to computer. All you have to do is accept and connection will be granted 🎉️

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This prompt didn't appear on my phone. As it turns out, that prompt doesn't works as expected on some custom ROMS. After some digging online, I came across this answer on stack overflow. Which leads to a commit message for (new) adb authentication implemented in 2012. This prompt copies ~/.android/adbkey.pub on computer, $ADB_VENDOR_KEYS, to /data/misc/adb/adb_keys file in phone's memory. since prompt isn't working for me I have to add that key manually 😕️

Littler harder way | copy-paste using Termux + root

Since /data/misc/adb/adb_keys file is offlimits for the user, we need root priviledges for this method.

1. Copy ~/.android/adbkey.pub to phone's memory
2. Open Termux and install sudo > pkg install tsu
3. Navigate to where file adbkey.pub is. I'm using Redmi Note 4 and its /sdcard directory is used for .
   File is at /sdcard/adbkey.pub in my case > cd /sdcard
4. Copy adbkey.pub to /data/misc/adb/adb_keys with sudo priviledges > sudo cp adbkey.pub /data/misc/adb/adb_keys
5. Double check if content of /data/misc/adb/adb_keys on phone and ~/.android/adbkey.pub on computer are the same
6. Enjoy 😊️

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Hard way | copy-paste using TWRP

This is the "no-root" hard method. You will still need root priviledges to edit /data/misc/adb/adb_keys. If your phone isn't rooted but has TWRP, GREAT. TWRP has root priviledges and a file manager.

1. Boot into TWRP by holding Vol+ and Power keys while the phone is turned off.
2. Connect phone to computer
3. Copy ~/.android/adbkey.pub to phone's memory
4. Go to Advanced > File manager
5. Navigate to where adbkey.pub was copied to. I am using Redmi Note 4 and MTP connects to /sdcard on this device.
6. Copy adbkey.pub to /data/misc/adb/adb_keys
7. Delete adb_keys in
8. Rename adbkey.pub to abd_keys
9. Double check if content of /data/misc/adb/adb_keys on phone and ~/.android/adbkey.pub on computer are the same
10. Enjoy 😊️

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It was a little annoying adventure for me to find where the adbkey.pub suppose to go. I am not immitated with having to do that thing manually. I was annoyed that this information isn't out there in Android documentations and requires reading answers from 2014 on stack overflow.

I hope this guide was helpful to you 😊️