Single line command to create self signed certificate

 

openssl req -x509 -newkey rsa:4096 -keyout key.pem -out cert.pem -sha256 -days 365 -nodes

Certificate with extensions:

openssl req -x509 -nodes -newkey rsa:2048 -keyout key.pem -out server.pem -days 7300 -subj '/CN=My Name/C=US/OU=My Unit/O=ACME' -addext "keyUsage = digitalSignature, keyEncipherment, dataEncipherment, cRLSign, keyCertSign" -addext "extendedKeyUsage = serverAuth, clientAuth"