I have the same issue when running adb devices command.
adb devices
List of devices attached
adb server version (36) doesn't match this client (40); killing...
* daemon started successfully
2322dc3d device
I ran command which adbwhich gave me the location of the adb that the previous command was using, in my case output was:
which adb
/usr/bin/adb
Then i ran whereis adb command which gave me the location of adb's:
whereis adb
adb: /usr/bin/adb /home/arefin/Android/Sdk/platform-tools/adb
/usr/share/man/man1/adb.1.gz
I get rid of this problem by moving the adb from /usr/bin directory with mv command: (meaning this is of no use thus instead of deleting just put in desktop),
/usr/bin$ `sudo mv adb /home/arefin/Desktop/`
After this i executed this command adb kill-server then ran adb devices. I found everything is fine this time.
My Android development related path in in $HOME/.profile file is, as below:
export ANDROID_HOME=/home/arefin/Android/Sdk
export PATH=$PATH:$ANDROID_HOME/platform-tools
export PATH=$PATH:$ANDROID_HOME/tools
export PATH=$PATH:$ANDROID_HOME/emulator
export PATH=$PATH:$JAVA_HOME/bin