add a certificate authority (CA) to Ubuntu

# cp /home/user/workspace/SecureCommunication/certs/valid3/cacert.pem /usr/local/share/ca-certificates/custom-cacert.crt

# update-ca-certificates

Updating certificates in /etc/ssl/certs... WARNING: Skipping duplicate certificate UbuntuOne-ValiCert_Class_2_VA.pem

WARNING: Skipping duplicate certificate UbuntuOne-ValiCert_Class_2_VA.pem

WARNING: Skipping duplicate certificate UbuntuOne-Go_Daddy_Class_2_CA.pem

WARNING: Skipping duplicate certificate UbuntuOne-Go_Daddy_Class_2_CA.pem

1 added, 0 removed; done.

Running hooks in /etc/ca-certificates/update.d....

Adding debian:custom-cacert.pem

done.

done.