SSL\/TLS is used to secure communication between a website and its visitors. When SSL\/TLS is configured, the website can be accessed using HTTPS<\/strong> instead of HTTP.<\/p>\n\n\n\n On a Linux server, SSL\/TLS configuration generally involves installing the required SSL certificate, configuring the web server, redirecting HTTP traffic to HTTPS, and verifying the certificate and TLS connection.<\/p>\n\n\n\n This guide explains some commonly used Linux commands to check SSL certificates, test HTTPS connectivity, and verify the web server configuration.<\/p>\n\n\n\n Before working with SSL\/TLS on a Linux server, make sure you have:<\/p>\n\n\n\n First, identify whether Apache or Nginx is running on the server.<\/p>\n\n\n\n For Apache:<\/p>\n\n\n\n On CentOS\/RHEL-based systems:<\/p>\n\n\n\n For Nginx:<\/p>\n\n\n\n These commands help verify whether the web server is running.<\/p>\n\n\n\n Use the following command to check whether the server is listening on the port 443:<\/p>\n\n\n\n You can also use:<\/p>\n\n\n\n If HTTPS is configured correctly, port Use A successful response may look similar to the following:<\/p>\n\n\n\n You can also use:<\/p>\n\n\n\n The The Run:<\/p>\n\n\n\n To display the certificate details:<\/p>\n\n\n\n This displays information such as the following:<\/p>\n\n\n\n To check when the certificate expires, use:<\/p>\n\n\n\n Example output:<\/p>\n\n\n\n The To verify the domain associated with the certificate:<\/p>\n\n\n\n This can help identify whether the certificate belongs to the expected domain.<\/p>\n\n\n\n Use the following command to check which Certificate Authority issued the certificate:<\/p>\n\n\n\n The output shows the certificate’s issuer.<\/p>\n\n\n\n To test a specific TLS version, you can use OpenSSL.<\/p>\n\n\n\n For TLS 1.2:<\/p>\n\n\n\n For TLS 1.3:<\/p>\n\n\n\n These commands can be used to verify whether the server supports the specified TLS version.<\/p>\n\n\n\n If HTTP traffic should redirect to HTTPS, run:<\/p>\n\n\n\n A correctly configured redirect may return:<\/p>\n\n\n\n This confirms that HTTP requests are being redirected to HTTPS.<\/p>\n\n\n\n The following command can be used for a quick HTTPS connection check:<\/p>\n\n\n\n It provides detailed information about the connection and helps identify common SSL\/TLS problems.<\/p>\n\n\n\n Check the certificate validity using:<\/p>\n\n\n\n If the Check port If there is no output, check the web server’s SSL configuration and service status.<\/p>\n\n\n\n Test the HTTP response:<\/p>\n\n\n\n If there is no Check the certificate subject:<\/p>\n\n\n\n Verify that the certificate is issued for the domain being accessed.<\/p>\n\n\n\n SSL\/TLS configuration on a Linux server involves more than installing a certificate. Administrators should also verify that HTTPS is listening on port 443, the certificate is valid, the domain matches the certificate, supported TLS versions are working, and HTTP traffic is correctly redirected to HTTPS.<\/p>\n\n\n\n Commands such as Use:<\/p>\n\n\n\n You can also check whether the port Run:<\/p>\n\n\n\n The Prerequisites<\/h2>\n\n\n\n
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Implementation<\/h2>\n\n\n\n
Step 1: Check the Web Server<\/h3>\n\n\n\n
systemctl status apache2<\/pre>\n\n\n\n
systemctl status httpd<\/pre>\n\n\n\n
systemctl status nginx<\/pre>\n\n\n\n
Step 2: Check Whether HTTPS Port 443 Is Listening<\/h3>\n\n\n\n
ss -lntp | grep :443<\/pre>\n\n\n\n
netstat -lntp | grep :443<\/pre>\n\n\n\n
443<\/code> should normally appear as a listening port.<\/p>\n\n\n\nStep 3: Test the HTTPS Connection Using curl<\/h3>\n\n\n\n
curl<\/code> to check whether the website is accessible through HTTPS:<\/p>\n\n\n\ncurl -I https:\/\/example.com<\/pre>\n\n\n\n
HTTP\/1.1 200 OK<\/pre>\n\n\n\n
curl -v https:\/\/example.com<\/pre>\n\n\n\n
-v<\/code> option displays detailed information about the HTTPS connection, including the TLS connection and certificate information.<\/p>\n\n\n\nStep 4: Check the SSL Certificate Using OpenSSL<\/h3>\n\n\n\n
openssl<\/code> command can be used to inspect the SSL\/TLS certificate presented by the website.<\/p>\n\n\n\nopenssl s_client -connect example.com:443<\/pre>\n\n\n\n
openssl s_client -connect example.com:443 <\/dev\/null 2>\/dev\/null | openssl x509 -noout -text<\/pre>\n\n\n\n
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Step 5: Check the Certificate Expiry Date<\/h3>\n\n\n\n
openssl s_client -connect example.com:443 <\/dev\/null 2>\/dev\/null | openssl x509 -noout -dates<\/pre>\n\n\n\n
notBefore=Jun 1 00:00:00 2026 GMT\nnotAfter=Aug 30 23:59:59 2026 GMT<\/pre>\n\n\n\n
notAfter<\/code> value indicates the certificate expiration date.<\/p>\n\n\n\nStep 6: Check the Certificate Subject<\/h3>\n\n\n\n
openssl s_client -connect example.com:443 <\/dev\/null 2>\/dev\/null | openssl x509 -noout -subject<\/pre>\n\n\n\n
Step 7: Check the Certificate Issuer<\/h3>\n\n\n\n
openssl s_client -connect example.com:443 <\/dev\/null 2>\/dev\/null | openssl x509 -noout -issuer<\/pre>\n\n\n\n
Step 8: Check the TLS Version<\/h3>\n\n\n\n
openssl s_client -connect example.com:443 -tls1_2<\/pre>\n\n\n\n
openssl s_client -connect example.com:443 -tls1_3<\/pre>\n\n\n\n
Step 9: Check HTTP to HTTPS Redirection<\/h3>\n\n\n\n
curl -I http:\/\/example.com<\/pre>\n\n\n\n
HTTP\/1.1 301 Moved Permanently\nLocation: https:\/\/example.com\/<\/pre>\n\n\n\n
Step 10: Test the Website Certificate and Connection<\/h3>\n\n\n\n
curl -Iv https:\/\/example.com<\/pre>\n\n\n\n
Common SSL\/TLS Commands<\/h2>\n\n\n\n
Purpose<\/th> Command<\/th><\/tr><\/thead> Check HTTPS port<\/td> ss -lntp | grep :443<\/code><\/td><\/tr>Test HTTPS<\/td> curl -I https:\/\/example.com<\/code><\/td><\/tr>Detailed HTTPS test<\/td> curl -v https:\/\/example.com<\/code><\/td><\/tr>Check the certificate.<\/td> openssl s_client -connect example.com:443<\/code><\/td><\/tr>Check certificate dates<\/td> openssl s_client -connect example.com:443 <\/dev\/null 2>\/dev\/null | openssl x509 -noout -dates<\/code><\/td><\/tr>Check certificate issuer<\/td> openssl s_client -connect example.com:443 <\/dev\/null 2>\/dev\/null | openssl x509 -noout -issuer<\/code><\/td><\/tr>Check certificate subject<\/td> openssl s_client -connect example.com:443 <\/dev\/null 2>\/dev\/null | openssl x509 -noout -subject<\/code><\/td><\/tr>Test TLS 1.2<\/td> openssl s_client -connect example.com:443 -tls1_2<\/code><\/td><\/tr>Test TLS 1.3<\/td> openssl s_client -connect example.com:443 -tls1_3<\/code><\/td><\/tr>Check HTTP redirect<\/td> curl -I http:\/\/example.com<\/code><\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\nCommon SSL\/TLS Issues<\/h2>\n\n\n\n
1. Certificate Expired<\/h3>\n\n\n\n
openssl s_client -connect example.com:443 <\/dev\/null 2>\/dev\/null | openssl x509 -noout -dates<\/pre>\n\n\n\n
notAfter<\/code> date has passed, the certificate needs to be renewed.<\/p>\n\n\n\n2. HTTPS Port Not Listening<\/h3>\n\n\n\n
443<\/code>:<\/p>\n\n\n\nss -lntp | grep :443<\/pre>\n\n\n\n
3. HTTP Not Redirecting to HTTPS<\/h3>\n\n\n\n
curl -I http:\/\/example.com<\/pre>\n\n\n\n
301<\/code> or 302 redirect to HTTPS, check the web server’s HTTP-to-HTTPS redirect configuration.<\/p>\n\n\n\n4. Certificate Does Not Match the Domain<\/h3>\n\n\n\n
openssl s_client -connect example.com:443 <\/dev\/null 2>\/dev\/null | openssl x509 -noout -subject<\/pre>\n\n\n\n
Conclusion<\/h2>\n\n\n\n
curl<\/code><\/strong>, openssl<\/code><\/strong>, ss<\/code><\/strong>, and systemctl<\/code><\/strong> can be used to troubleshoot and verify SSL\/TLS configuration directly from the Linux server.<\/p>\n\n\n\nFAQs<\/h2>\n\n\n\n
1. How can I check whether HTTPS is working on a Linux server?<\/h3>\n\n\n\n
curl -I https:\/\/example.com<\/pre>\n\n\n\n
443<\/code> is listening:<\/p>\n\n\n\nss -lntp | grep :443<\/pre>\n\n\n\n
2. How can I check when an SSL certificate expires?<\/h3>\n\n\n\n
openssl s_client -connect example.com:443 <\/dev\/null 2>\/dev\/null | openssl x509 -noout -dates<\/pre>\n\n\n\n
notAfter<\/code> value shows the certificate expiration date.<\/p>\n\n\n\nRelated Articles<\/h2>\n\n\n\n