OpenSSL
Get Cert start/expiry
openssl x509 -noout -in cert.crt -dates
Get cert Subject/CN
openssl x509 -noout -in cert.crt -subject
Convert PEM and plain text key to PKCS12/P12 format
openssl pkcs12 -export -out cert.pfx -inkey cert.key -in cert.crt
s_client for telnet-like troubleshooting for SSL connections
See Linux Web Troubleshooting#OpenSSL s_client for telnet-like troubleshooting for SSL connections
Generate server key and CSR for purchasing SSL cert
Generate RSA key, key size 4096 bytes, without encryption to avoid requiring to enter a password when starting the daemon:
openssl genrsa -out domainname.key 4096
Generate the CSR:
openssl req -new -key domainname.key -out domainname.csr