Troubleshooting OpenVPN Server Certificate Errors: A Quick Guide

Encountering issues with your Openvpn Server certificate can be a common hurdle, especially when setting up secure connections. Users often face errors during the initial configuration, and log outputs like the one below can be perplexing. This guide breaks down a typical certificate loading error in OpenVPN and points towards potential solutions to get your server running smoothly.

The error message:

Sun Jul 24 08:47:52 2011 OpenVPN 2.2.0 i686-pc-linux-gnu [SSL] [LZO2] [EPOLL] [eurephia] built on May 14 2011
Sun Jul 24 08:47:52 2011 NOTE: your local LAN uses the extremely common subnet address 192.168.0.x or 192.168.1.x. Be aware that this might create routing conflicts if you connect to the VPN server from public locations such as internet cafes that use the same subnet.
Sun Jul 24 08:47:52 2011 NOTE: OpenVPN 2.1 requires '--script-security 2' or higher to call user-defined scripts or executables
Sun Jul 24 08:47:52 2011 Diffie-Hellman initialized with 1024 bit key
Sun Jul 24 08:47:52 2011 Cannot load certificate file Core.crt: error:0906D06C:PEM routines:PEM_read_bio:no start line: error:140AD009:SSL routines:SSL_CTX_use_certificate_file:PEM lib
Sun Jul 24 08:47:52 2011 Exiting

This “Cannot load certificate file” error, specifically mentioning “PEM routines:PEM_read_bio:no start line,” indicates that OpenVPN is unable to read your Core.crt certificate file. This often happens due to issues during certificate generation or file path problems in your OpenVPN server configuration file.

The user attempted certificate creation using commands like:

source ./vars
./clean-all
./build-ca
./build-key Core
./build-key-server Core
./build-dh

While these commands are generally correct for building certificates with Easy-RSA, the error suggests a problem with the generated Core.crt file itself or how OpenVPN is accessing it.

Troubleshooting Steps:

1. Verify Certificate Generation: Double-check that the certificate generation scripts executed without errors. Look for any error messages during the ./build-ca, ./build-key, and ./build-key-server steps.

2. File Path Accuracy: Ensure the cert directive in your OpenVPN server configuration file (server.conf) correctly points to the location of your Core.crt file. Relative paths can be tricky, so using absolute paths is often more reliable.

3. File Permissions: Confirm that the OpenVPN server process has the necessary permissions to read the Core.crt file. Incorrect file permissions can prevent OpenVPN from accessing the certificate.

4. Certificate Content: Inspect the Core.crt file itself. Open it with a text editor and ensure it begins with -----BEGIN CERTIFICATE----- and ends with -----END CERTIFICATE-----. A missing start or end line, as indicated by the “no start line” error, would cause this problem. Regenerate the certificate if the content is corrupted.

By systematically checking these points, you can usually resolve the “Cannot load certificate file” error and get your OpenVPN server operational. Remember to consult the official OpenVPN documentation for detailed guidance on server setup and certificate management.