root@ubuntu:~# systemctl restart proftpd.service
Job for proftpd.service failed because the control process exited with error code. See "systemctl status proftpd.service" and "journalctl -xe" for details.

#
# Proftpd sample configuration for FTPS connections.
#
# Note that FTPS impose some limitations in NAT traversing.
# See http://www.castaglia.org/proftpd/doc/contrib/ProFTPD-mini-HOWTO-TLS.html
# for more information.
#

<IfModule mod_tls.c>
TLSEngine                               on
TLSLog                                  /var/log/proftpd/tls.log
TLSProtocol                             SSLv23
#TLSCipherSuit AES128+EECDH:AES128+EDH
#TLSOptions                              NoCertRequest AllowClientRenegotiations
#TLSRSACertificateFile                   /etc/proftpd/ssl/proftpd.cert.pem
#TSLRSACertificateKeyFile                /etc/proftpd/ssl/proftpd.key.pem
#TLSVerifyClient                         off
#TLSRequired                             on
#RequireValidShell                       no
# a command like:
#
# openssl req -x509 -newkey rsa:1024 \
#          -keyout /etc/ssl/private/proftpd.key -out /etc/ssl/certs/proftpd.crt$
#          -nodes -days 365
#
# The proftpd.key file must be readable by root only. The other file can be
# readable by anyone.
#
 chmod 0600 /etc/ssl/private/proftpd.key
 chmod 0640 /etc/ssl/private/proftpd.key
#
TLSRSACertificateFile                   /etc/ssl/certs/proftpd.crt
TLSRSACertificateKeyFile                /etc/ssl/private/proftpd.key
#
# CA the server trusts...
TLSCACertificateFile                     /etc/ssl/certs/CA.pem
# ...or avoid CA cert and be verbose
TLSOptions                      NoCertRequest EnableDiags
 chmod 0640 /etc/ssl/private/proftpd.key
#
TLSRSACertificateFile                   /etc/ssl/certs/proftpd.crt
TLSRSACertificateKeyFile                /etc/ssl/private/proftpd.key
#
# CA the server trusts...
TLSCACertificateFile                     /etc/ssl/certs/CA.pem
# ...or avoid CA cert and be verbose
TLSOptions                      NoCertRequest EnableDiags
# ... or the same with relaxed session use for some clients (e.g. FireFtp)
TLSOptions                      NoCertRequest EnableDiags NoSessionReuseRequired
#
#
# Per default drop connection if client tries to start a renegotiate
# This is a fix for CVE-2009-3555 but could break some clients.
#
TLSOptions                                                      AllowClientRene$
#
# Authenticate clients that want to use FTP over TLS?
TLSOptions                      NoCertRequest EnableDiags NoSessionReuseRequired
#
#
# Per default drop connection if client tries to start a renegotiate
# This is a fix for CVE-2009-3555 but could break some clients.
#
TLSOptions                                                      AllowClientRene$
#
# Authenticate clients that want to use FTP over TLS?
#
TLSVerifyClient                         off
#
# Are clients required to use FTP over TLS when talking to this server?
#
TLSRequired                             off
#
# Allow SSL/TLS renegotiations when the client requests them, but
# do not force the renegotations.  Some clients do not support
# SSL/TLS renegotiations; when mod_tls forces a renegotiation, these
TLSVerifyClient                         off
#
# Are clients required to use FTP over TLS when talking to this server?
#
TLSRequired                             off
#
# Allow SSL/TLS renegotiations when the client requests them, but
# do not force the renegotations.  Some clients do not support
# SSL/TLS renegotiations; when mod_tls forces a renegotiation, these
# clients will close the data connection, or there will be a timeout
# on an idle data connection.
#
TLSRenegotiate                          required off
</IfModule>