I don't remember how many times I encountered this problem when I learned to debug Android programs with adb commands:

Open Eclipse or Android Studio and find that no device can be found. Then enter the command adb shell in the dos window. The following problems occur:

adb devicesadb server is out of date.  killing...
ADB server didn't ACK* failed to start daemon *error: unknown host service

Every God on the Internet explains why: the port of adb (5037) is occupied.

After trying various methods, the general method can solve the problem:

In the cmd window:

C:\Users\xiaoming>adb nodaemon server
cannot bind 'tcp:5037'

C:\Users\xiaoming>netstat -ano | findstr "5037"
  TCP    127.0.0.1:5037         0.0.0.0:0              LISTENING       8516
  TCP    127.0.0.1:5037         127.0.0.1:59163        TIME_WAIT       0
  TCP    127.0.0.1:5037         127.0.0.1:59164        TIME_WAIT       0
  TCP    127.0.0.1:5037         127.0.0.1:59167        TIME_WAIT       0
  ......
C:\Users\xiaoming>tasklist | findstr "8516"
sjk_daemon                        8516 Console                    1     3,071 K

Oh, it turns out that the sjk_daemon process takes up the port of the adb.

C:\Users\xiaoming>tasklist

Image Name                     PID Session Name        Session#    Mem Usage
========================= ======== ================ =========== ============
System Idle Process              0 Services                   0         24 K
System                           4 Services                   0      1,128 K
sjk_daemon                     963 Console                    1      3,071 K
tasklist.exe                  1260 Console                    1      5,856 K

kill this process:

C:\Users\xiaoming>taskkill /f /pid 963

If this command prompt has no privileges, you can go to the window of "process" in the "task manager" of windows, find the process and kill it.

If you run adb devices again, there will be no problem.

C:\Users\xiaoming>adb devices
4df7f482396a301d        device

This is online. https://blog.csdn.net/liranke/article/details/42524851#reply This elder brother's solution, but I found that using windows Task Manager to kill this process does not work, so I still hope to be able to kill the process in the dos window is more useful!