SSL Certificate Problem: unable to get local issuer certificate

I am having small initramfs with static busybox into it. The sole purpose of this initramfs is to download/upload files to the HTTPS server. I have the proper certificate and credentials to do so. But when I execute the command: curl --cacert /tmp/filename.pem -T /tmp/file_to_upload -u user:pass https://Server_name/ I greeted with an error: curl: (60) SSL certificate problem: unable to get local issuer certificate If I use the same command with same certificate onto Ubuntu, then everything goes smooth. How am I suppose to resolve this issue ? **EDIT:** I do not want to use "-k" or "--insecure" switch **NOTE:** I do not have openssl or /etc/ssl directory into initramfs