Ubuntu/openssl

common openssl commands http://www.sslshopper.com/article-most-common-openssl-commands.html

generating a SSL cert with a SAN http://apetec.com/support/GenerateSAN-CSR.htm

Generating SAN Certificate

Oracle Linux

find openssl.cnf. I found it located at:

/etc/pki/tls/openssl.cnf

Verify this is present and uncommented:

[req]
distinguished_name = req_distinguished_name
req_extensions = v3_req

You'll probably need to add the following:

[ v3_req ]
subjectAltName = @alt_names

[alt_names]
DNS.1 = domain1.com
DNS.2 = sub.domain1.com
DNS.3 = domain2.com

Now we need to create the Key, CSR, and CRT

~$ openssl genrsa -out san_domain_com.key 2048
~$ openssl req -new -out san_domain_com.csr -key san_domain_com.key -config openssl.cnf
~$ openssl x509 -req -days 3650 -in san_domain_com.csr -signkey san_domain_com.key -out san_domain_com.crt -extensions v3_req -extfile openssl.cnf