How to troubleshoot a 'Connection Refused' error?
Jul 11, 2025 am 02:06 AMWhen encountering a "Connection Refused" error, the most direct meaning is that the target host or service you are trying to connect to explicitly reject your request. 1. Check whether the target service is running. Log in to the target machine to check the service status using systemctl status or ps aux. If it is not started, start manually; 2. Confirm whether the port is listening correctly, use the netstat or ss command to check whether the service is listening to the correct port, modify the configuration file if necessary and restart the service; 3. Firewall and security group settings may cause connection denied, check the local firewall rules and cloud platform security group configuration, and temporarily close the firewall during testing; 4. IP address or DNS resolution errors may also cause problems. Use ping or nslookup to ensure that the domain name resolution is correct, and the IP and port used in the connection command are correct. Troubleshooting is recommended in sequence, most of which are configuration or service status issues, rather than network transmission failures.
When encountering a "Connection Refused" error, the most direct meaning is that the target host or service you are trying to connect to explicitly reject your request. This is usually not a problem during network transmission, but rather the target side itself does not accept connections. The following are several common troubleshooting directions and solutions.
1. Check whether the target service is running
The most common reason is that the service you want to connect to is not running at all. For example, you want to connect to the server through SSH, but sshd is not started; or you want to connect to the database, but the MySQL/PostgreSQL service is hung.
- Log in to the target machine and check the service status:
- Linux system can use
systemctl status ssh
orps aux | grep sshd
- For database, you can see if the corresponding service is running
- Linux system can use
- If the service is not started, try starting it manually:
- For example,
sudo systemctl start ssh
- For example,
If you do not have permission to access the target machine, contact the administrator to confirm the service status.
2. Confirm whether the port is monitored correctly
Even if the service is running, it may not be listening for the correct port. You can use netstat
or ss
command to check:
sudo netstat -tuln | grep :22
or:
sudo ss -tuln | grep :22
If you cannot see an output similar to 0.0.0.0:22
or [::]:22
, it means that the service is not listening to this port normally.
- Check whether the configuration file has changed the default port (for example, SSH default is 22, but if it has changed it to 2222)
- Remember to restart the service after modification
3. Firewall and security group settings
Although "Connection Refused" is not usually a problem with network routing, the security group of a firewall or cloud platform may also lead to this result if it is not configured properly.
- Check the local firewall on the target machine:
-
sudo iptables -L -n
or useufw status
-
- If it is a cloud server (such as AWS, Alibaba Cloud), check whether the security group rules have released the port you want to connect to.
- During testing, you can temporarily close the firewall and test it (such as
sudo ufw disable
)
Note: Do not release all traffic at will when opening the port, and maintain the principle of minimization.
4. Is the IP address or DNS resolution correct?
Sometimes we think we are connected to the right address, but in fact we may have written the wrong IP or the domain name resolution problem.
- Use
ping
ornslookup
to check whether the domain name has resolved the expected IP - Make sure that the IP and port you use in the connection command are correct, such as:
- Error:
ssh user@wrong-ip
- Correct:
ssh user@correct-ip -p 2222
(if the port is not the default)
- Error:
Basically these common reasons. The recommended order of troubleshooting is: first confirm whether the service is running, then check whether the port is listening, and then check whether the firewall and IP are correct. This error seems scary, but most of the time it is a problem of configuration or service status. It is not complicated, but it is easy to ignore details.
The above is the detailed content of How to troubleshoot a 'Connection Refused' error?. For more information, please follow other related articles on the PHP Chinese website!

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