When setting up vsftpd we have problems with it not providing a trusted connection us a basic pem certificate container using just our private key and certificate.
We created our pem file with the following commands.
cat somecert.com.crt >> somepem.pem
cat somecertkey.com.key >> somepem.pem
SSL Certificate config vsftpd.conf
When connecting using lftp in debug mode I saw that we giving a certificate with out enough info to be establish the full chain of authority. To ensure it was trusted.
lftp -d -u user:pass myserver.com
ERROR: Certificate verification: Not trusted
**** Certificate verification: Not trusted
---- Closing control socket