The following error is noted while running adb:

$ adb shell
adb server version (41) doesn’t match this client (39); killing…
ADB server didn’t ACK
Full server startup log: /tmp/adb.1000.log
Server had pid: 19748
— adb starting (pid 19748) —
adb I 04-06 12:07:01 19748 19748 main.cpp:57] Android Debug Bridge version 1.0.39
adb I 04-06 12:07:01 19748 19748 main.cpp:57] Version 1:8.1.0+r23-5~18.04
adb I 04-06 12:07:01 19748 19748 main.cpp:57] Installed as /usr/lib/android-sdk/platform-tools/adb
adb I 04-06 12:07:01 19748 19748 main.cpp:57]
adb I 04-06 12:07:01 19748 19748 adb_auth_host.cpp:416] adb_auth_init…
adb I 04-06 12:07:01 19748 19748 adb_auth_host.cpp:174] read_key_file ‘/home/joel/.android/adbkey’…
adb I 04-06 12:07:01 19748 19748 adb_auth_host.cpp:391] adb_auth_inotify_init…
adb I 04-06 12:07:01 19748 19748 adb_auth_host.cpp:467] Calling send_auth_response
adb I 04-06 12:07:01 19748 19748 adb_auth_host.cpp:467] Calling send_auth_response
adb server killed by remote request

failed to start daemon error: cannot connect to daemon

The error is because of adb version. Use the adb that comes with Android SDK.

$ adb –version
Android Debug Bridge version 1.0.39
Version 1:8.1.0+r23-5~18.04
Installed as /usr/lib/android-sdk/platform-tools/adb

To fix:

/home/joel/Android/Sdk/platform-tools/adb --version
 Android Debug Bridge version 1.0.41
 Version 29.0.6-6198805
 Installed as /home/joel/Android/Sdk/platform-tools/adb
 [email protected]:/home/joel# cp /home/joel/Android/Sdk/platform-tools/adb /usr/bin/[email protected]:/home/joel# adb
 Android Debug Bridge version 1.0.41
 Version 29.0.6-6198805
 Installed as /usr/bin/adb

#adb devices
 List of devices attached
 20da0e00    device
 emulator-5554    device

#adb -s 20da0e00 shell
 OnePlus6:/