Installing the certificate in such ways didn't worked for me (later I've realized I had to rename my lacking certificate to .ctr to append it into /etc/ssl/certs/ca-certificates.crt through dpkg-reconfigure ca-certificates).   The solution for this problem is to copy the lacking certificate into the store of certificates used by PulseSecure.   In my case I was missing the intermediate certificate: DigiCert Global CA G2, I realized that by using this command:   openssl s_client -connect <IP of my VPN CGI> An error was displayed:     subject=/C=XX/ST=XXXXX (our certificate) issuer=/C=US/O=DigiCert Inc/CN=DigiCert GLobal CA G2 Verify return code: 21 (unable to verify the first certificate)   Copied the text certificate from: TBS-Certificates   In the file on /usr/local/pulse/README says which store is used for each operating system (Ubuntu in my case) so I edited it:     cp /etc/ssl/certs/ca-certificates.crt /etc/ssl/certs/ca-certificates.crt.backup vim /etc/ssl/certs/ca-certificates.crt   Copied and pasted the lacking certificate into it (at the start of ca-certificates.crt)   Started again Pulse Secure and everything worked. Documented this if someone else needs to solve a similar problem. Regards. Helfgott   EDIT: This process also works:   sudo mkdir /usr/share/ca-certificates/extra sudo cp <YOUR_CERTIFICATE>.crt /usr/share/ca-certificates/extra/ sudo dpkg-reconfigure ca-certificates But the certificate must be ".crt" otherwise won't be added in ca-certificates store.   ... View more