When I run 'React', it says that port 3000 is in use

Question

I know that many methods have already come out as solutions. However, as you can see in the picture, when I search for port 3000 in 'cmd', the process in use does not appear. In the case of 8080, it comes out well because the Spring Boot server is running, but in the case of 'React', even if there is no process using port 3000 as shown in the picture, 'Something is already running on port 3000'. is printed out.

enter image description here

I'm using a translator so it might be difficult to understand, but any help would be appreciated.

score 0 · Accepted Answer · answered May 31 '22 at 08:19

0

Have you tried:

Running cmd as admin

Using :3000 instead of 3000

taskkill /PID <PID> /F kills the process, just replace with the PID, to the right of "listening".

If none works, you could just restart the pc.

NOTE: some people have encountered this error even after restarting, but managed to solve the problem with this command: npx kill-port 3000

answered May 31 '22 at 08:19

eskiltb

92
8

Thanks for your reply. I tried both methods, but it didn't work. I also tried rebooting the computer several times, but it didn't work. – 프리view May 31 '22 at 08:43
`npx kill-port 3000` did not work either? – eskiltb May 31 '22 at 08:48
"npx kill-port 3000" was executed. After that, I tried "npm start" but got the same error. – 프리view May 31 '22 at 09:02
`lsof -i:[PORT]` maybe? – eskiltb May 31 '22 at 09:05
I'm not familiar with the cmd command. Can it be used on Windows operating systems? – 프리view May 31 '22 at 09:08
not 100% sure, I'm using a Mac. Might as well just try? – eskiltb May 31 '22 at 09:08
I run it from cmd but it says it is not available. It doesn't seem to work on Windows. – 프리view May 31 '22 at 09:11
Can you try using `netstat -lp` to see if the process shows up? – eskiltb May 31 '22 at 09:14
And `netstat -an | grep 3000` – eskiltb May 31 '22 at 09:15
"grep" says the command is not available. – 프리view May 31 '22 at 09:18
have you tried `netstat -lp` ? Or `netstat -tupna`? – eskiltb May 31 '22 at 09:20
"NETSTAT [-a] [-b] [-e] [-f] [-i] [-n] [-o] [-p proto] [-r] [-s] [-t] [-x ] [-y] [interval]" A description is given for each. – 프리view May 31 '22 at 09:21
What do you mean? I asked if you tried writing `netstat -lp` or `netstat -tupma` to see if the port PID shows up – eskiltb May 31 '22 at 09:26
Only commands that can be used in "netstat" and their descriptions are displayed. – 프리view May 31 '22 at 09:30
Try reading this: https://stackoverflow.com/questions/63257991/port-not-shown-to-be-used-in-netstat-but-trying-to-use-the-port-is-denied-by-wi – eskiltb May 31 '22 at 09:35
The article told me to activate "Hyper-V", so I installed "Hyper-V" in the cmd window and rebooted, and it worked. Thank you so much for your help for a long time. – 프리view May 31 '22 at 09:46
No problem, glad it worked out – eskiltb May 31 '22 at 09:47

score 0 · Answer 2 · answered May 31 '22 at 08:21

0

This means you have launched another instance before... Switching off the computer can work but there is another solution In windows, just open the Ressource Monitor (Task Manager -> Performance ->Open Ressource Monitor) then open the Listening port and check if 3000 is already running

answered May 31 '22 at 08:21

Ingenious_Hans

724
5
16

It was understood to mean "open a closed port". I searched the internet and tried to follow, but to no avail. – 프리view May 31 '22 at 09:04

When I run 'React', it says that port 3000 is in use

2 Answers2