[postgres@centos7 ~]$ mkdir ~/openssl
[postgres@centos7 ~]$ openssl req -new -x509 -days 365 -nodes -text -subj '/CN=postgres' -out ~/openssl/server.crt -keyout ~/openssl/server.key
Generating a 2048 bit RSA private key
.............+++
.+++
writing new private key to '/home/postgres/openssl/server.key'
-----
[postgres@centos7 ~]$ chmod 600 ~/openssl/server.key
[postgres@centos7 ~]$ ll openssl/
total 8
-rw-rw-r-- 1 postgres postgres 4058 Nov 11 08:16 server.crt
-rw------- 1 postgres postgres 1704 Nov 11 08:16 server.key
[postgres@centos7 ~]$