If you're about to handle X509 certificates and don't want to remember/google a handful of openssl commands you can use the graphical tool XCA Show archive.org snapshot .

Setup

1. Install XCA sudo apt install xca
2. Create a new database with a strong master password

Features

• Create CSR
• Verify SSL private key matches SSL certificate
  • enable Key name column
  • import certificate and private key
• Import, export and convert PKCS#12, PKCS#7, PEM chain, DER and more
• Check issuer chain
  • import certificate, intermediate and root ca
  • they get automatically chained
• View certificates and export openssl config
• Check revocation lists
• Setup a private PKI
• A lot more...