Stata internet commands and the OS TLS/DNS stack: distinguishing certificate failures from DNS errors

Answering the exact question

Stata does not expose a setting, return code, or diagnostic output that distinguishes between DNS resolution failures, proxy‑related problems, and TLS/SSL certificate validation errors for its internet commands (e.g., copy, urlfetch, webuse, ssc install). The only Stata‑level result is a generic _rc of 0 (success) or 1 (failure), and the error message is generated by the host operating system’s networking stack. This behaviour is identical across Windows, macOS, and Linux builds of the same Stata release because the commands delegate entirely to the OS.

Confirmed facts

• Stata forwards all network traffic to the OS resolver and TLS stack; it has no built‑in DNS or CA store.
• Stata’s error messages are OS‑dependent and vary in wording between releases and platforms.
• There is no documented Stata option to disable certificate checks or point to a custom CA bundle.
• Proxy configuration is inherited from the environment or OS settings; Stata does not expose a proxy API.

Minimal supported approach to identify the failure layer

1. Run the Stata command with capture to suppress the generic error text.

   capture copy https://example.com/file.txt ./file.txt
   if _rc {
       display "Stata reported a failure (rc = ``_rc``)"
   }
   

2. Check DNS resolution from the same shell.

   nslookup example.com
   # or
    dig +short example.com
   

   If the lookup fails or returns an unexpected IP, the problem is DNS.

3. Test the TLS handshake independently.

   openssl s_client -connect example.com:443 -servername example.com 2>/dev/null | openssl x509 -noout -issuer -subject
   

   Look for messages such as certificate verify failed or unable to get local issuer certificate. A failure here points to a certificate issue; a successful handshake suggests the TLS layer is fine.

4. Verify proxy settings.

   # Unix‑like shells
   echo $http_proxy
   echo $https_proxy
   # Windows PowerShell
   [Environment]::GetEnvironmentVariable("http_proxy")
   [Environment]::GetEnvironmentVariable("https_proxy")
   

   Compare these values with the proxy configuration shown in your OS’s network settings. If Stata inherits a proxy that is mis‑configured or unreachable, the command will fail even if DNS and TLS succeed.

5. Cross‑check with a browser or another tool.

   Open the URL in a web browser or use wget/curl to confirm whether the failure is reproducible outside Stata. Consistency across tools confirms that the issue lies in the OS networking stack, not Stata.

When to ask for more information

If the steps above still leave ambiguity—e.g., nslookup succeeds but openssl reports a TLS error that Stata does not surface—please share the exact error text from openssl s_client. That detail can clarify whether the certificate chain is incomplete or the server requires client authentication.

Bottom line

Because Stata relies on the host OS for all networking, you cannot rely on a Stata‑level diagnostic to separate DNS, proxy, or TLS failures. The practical, repeatable method is to perform the three external checks above and compare the results. Once you isolate the layer that fails, you can address DNS mis‑configuration, adjust proxy settings, or update the system’s CA bundle accordingly.