>>> openssl version
>>> mkdir cert
>>> openssl genrsa -out cert/server_key.pem 2048
>>> chmod 600 cert/server_key.pem
>>> openssl req -new -key cert/server_key.pem -out cert/server_csr.pem
>>> openssl req -text -noout -verify -in cert/server_csr.pem
>>> openssl x509 -req -days 365 -in cert/server_csr.pem -signkey cert/server_key.pem -out cert/server_cert.pem
-day指有效期