The following error appeared upon upgrading JRuby:
OpenSSL::X509::StoreError: setting default path failed: Invalid keystore format
wget http://curl.haxx.se/ca/cacert.pem
sudo keytool -importcert -file cacert.pem -keystore /Users/youruser/.keystore
export SSL_CERT_FILE=/Users/youruser/.keystore
jruby -S gem install whatever
❤️ https://gist.github.com/kendagriff/adec3713b4dfe6a1abdf#gistcomment-1933072 this is EXACTLY how to fix. I have been dealing with this issue for months and setting that cert file every time.
/Library/Java/JavaVirtualMachines
export SSL_CERT_FILE=/Users/youruser/.keystore