Error starting userland proxy: listen TCP 0.0.0.0:80: bind: address already in use
today, it was found that port 80 was occupied on Ali’s server. The advantages are inexplicable. An investigation found that the process aliyundun occupied the port

tcp          100.100.100.200:80      TIME_WAIT   -                   
tcp          100.100.30.25:80        ESTABLISHED 1472/AliYunDun      
tcp          100.100.100.200:80      TIME_WAIT   -          

Displaying with kill is not allowed

[root@lingg ~]# kill 1472
-bash: kill: (1472) - Disallowed operations
[root@lingg ~]# kill -9 1472
-bash: kill: (1472) - Disallowed operations

Then I found the solution online as follows

sudo fuser -k 80/tcp

```bash
[root@lingg ~]# sudo fuser -k 80/tcp
80/tcp:               1267  1272  1273  1274

Done!