Clash Common Error Codes: Connection Timeout, Certificate Error, DNS Failure Explained
Table of Contents
Understanding Clash Error Codes and Log Levels
Before diving into specific clash common error codes, you must understand how to read the logs. The default log level often hides the exact failure reason. By adjusting the log level, you can expose the underlying network stack errors.
Open your Clash configuration file and locate the log-level parameter. Change it from info to debug.
log-level: debugRestart the Clash core. The console or log panel will now display detailed handshake failures, DNS lookup errors, and routing decisions. For a comprehensive breakdown of how to interpret these logs, refer to our log analysis guide.
Connection Timeout Errors
Errors containing ETIMEDOUT or connection timed out indicate that the client attempted to establish a TCP connection to the proxy server but received no response within the expected timeframe. This is a network-layer issue, not a configuration syntax error.
A timeout does not necessarily mean the server is offline. It often indicates that the port is blocked by a local firewall, an ISP filter, or the server's own firewall rules.
First, verify the server IP and port in your configuration. Use a tool like telnet or tcping from your local machine to test raw connectivity to the server IP and port.
telnet 198.51.100.1 443If the connection hangs, the issue is network-level. If you need deeper assistance with node connectivity, our node connection troubleshooting guide covers advanced routing and firewall bypass techniques.
TLS and Certificate Errors
Errors containing x509: certificate signed by unknown authority or CERTIFICATE_VERIFY_FAILED indicate that the TLS handshake failed because the client cannot verify the server's certificate chain.
Disabling certificate verification exposes your traffic to man-in-the-middle attacks. Only use skip-cert-verify: true for testing or when connecting to servers with self-signed certificates in a trusted environment.
Ensure the sni parameter matches the server's domain name exactly. If the server uses a self-signed certificate, you can bypass the check temporarily.
proxies:
- name: "TLS Node"
type: trojan
server: example.com
port: 443
password: "password"
sni: example.com
skip-cert-verify: trueIf you are managing your own VPS, generate a valid certificate using Let's Encrypt. This eliminates the need for skip-cert-verify and improves compatibility with strict clients and corporate firewalls.
DNS Resolution Failures
When you see lookup domain.com: no such host or DNS lookup failed, the issue lies in the DNS resolution phase. This often happens when the local DNS server is blocked, or the fake-ip cache is corrupted.
In mihomo-based clients, DNS resolution is handled internally. If dns.enable is set to false, Clash relies entirely on the system DNS, which is frequently blocked by local firewalls or poisoned by the ISP.
Enable the internal DNS resolver and use fake-ip mode to prevent DNS leaks and improve routing speed.
dns:
enable: true
enhanced-mode: fake-ip
fake-ip-range: 198.18.0.1/16
fake-ip-filter:
- "*.lan"
- "*.local"
- "*.msftconnecttest.com"
nameserver:
- 223.5.5.5
- 8.8.8.8Proxy Protocol and Handshake Failures
Errors like connection reset by peer or EOF during the handshake phase usually mean a protocol mismatch. The server rejected the client's initial greeting because the protocol, encryption method, or authentication parameters do not match.
Check your proxy node configuration. Ensure that the type (e.g., vmess, vless, trojan) matches the server setup. For VLESS and Trojan, verify the flow and security parameters. A common mistake is using a Trojan configuration to connect to a VMess server.
Subscription and Profile Parsing Errors
Errors like failed to parse config or yaml: line X: mapping values are not allowed in this context mean the configuration file itself is malformed. This is common when importing subscriptions.
Often, the subscription URL returns an HTML error page instead of a YAML file, or the provider uses an unsupported syntax. For detailed steps on how to fix broken subscription URLs and convert formats, check our subscription import fixes guide.
Copy the raw content of your configuration file and paste it into a YAML validator. Look for incorrect indentation, missing colons, or unescaped special characters in passwords.
System-Level and Network Stack Issues
When using TUN mode, you might encounter permission denied or operation not permitted. These errors occur because TUN mode requires raw socket access to create virtual network interfaces.
On Linux and macOS, the Clash core must be run with root privileges or granted the CAP_NET_ADMIN capability to use TUN mode. On Windows, run the client as Administrator.
tun:
enable: true
stack: system
auto-route: true
auto-detect-interface: trueAdvanced Debugging and Verification Checklist
If you have followed the specific fixes above and are still experiencing clash common error codes, use this systematic checklist to isolate the problem.
- Verify Core Version: Ensure you are using the latest mihomo core. Older versions may lack support for newer protocol extensions like Reality or VLESS.
- Check System Time: TLS handshakes will fail if your system clock is out of sync by more than a few minutes. Enable NTP synchronization.
- Test Direct Connection: Temporarily disable the proxy and ping the server IP. If the IP is unreachable, the issue is your local network or the server is down.
- Review Firewall Rules: Ensure your local firewall or ISP is not blocking the specific ports used by your proxy nodes.
By methodically checking these areas and utilizing the debug logs, you can resolve almost any proxy connection issue. For deeper log inspection, revisit the log analysis guide to trace the exact point of failure in the network stack.