From: http://0pointer.de/blog/projects/systemd-for-admins-3.html

Also: http://0pointer.de/blog/projects/systemd-for-admins-2.html

How Do I Convert A SysV Init Script Into A systemd Service File?

From the information extracted above we can now write our systemd service file:

[Unit]
Description=Daemon to detect crashing apps
After=syslog.target

[Service]
ExecStart=/usr/sbin/abrtd
Type=forking

[Install]
WantedBy=multi-user.target


Second vsftpd_2.conf
listen=YES
anonymous_enable=NO
local_enable=YES
write_enable=YES
dirmessage_enable=YES
use_localtime=YES
xferlog_enable=YES
connect_from_port_20=YES
listen_port=21
user_sub_token=$USER
pasv_enable=YES
pasv_min_port=40101
pasv_max_port=40200
#pasv_address=1.1.1.1
userlist_enable=YES
userlist_file=/etc/vsftpd.userlist
userlist_deny=NO

# This option should be the name of a directory which is empty.  Also, the
# directory should not be writable by the ftp user. This directory is used
# as a secure chroot() jail at times vsftpd does not require filesystem
# access.
secure_chroot_dir=/var/run/vsftpd/empty
#
# This string is the name of the PAM service vsftpd will use.
pam_service_name=vsftpd
#
# This option specifies the location of the RSA certificate to use for SSL
# encrypted connections.
#rsa_cert_file=/etc/ssl/certs/ssl-cert-snakeoil.pem
#rsa_private_key_file=/etc/ssl/private/ssl-cert-snakeoil.key
#ssl_enable=NO

#
# Uncomment this to indicate that vsftpd use a utf8 filesystem.
#utf8_filesystem=YES


Ubuntu
load the systemd service file to:

/lib/systemd/system

[Unit]
Description=vsftpd FTP server
After=network.target

[Service]
Type=simple
ExecStart=/usr/sbin/vsftpd /etc/vsftpd_internal_21.conf
ExecReload=/bin/kill -HUP $MAINPID
ExecStartPre=-/bin/mkdir -p /var/run/vsftpd/empty

[Install]
WantedBy=multi-user.target

From : https://superuser.com/questions/819181/vsftpd-returns-wrong-pasv-address

pasv_addr_resolve=YES
Then you should be able to put a hostname instead of an IP address as the pasv_address. pasv_addr_resolv defaults to NO.

From: https://help.ubuntu.com/community/vsftpd

Virtual users with TLS/SSL/FTPS and a common upload directory - Complicated VSFTPD
Virtual users are users that do not exist on the system - they are not in /etc/passwd, do not 
have a home directory on the system, can not login but in vsftpd - or if they do exist, they 
can login in vsftpd with a non system password - security. 

You can set different definitions to each virtual user, granting to each of these users different 
permissions. If TLS/SSL/FTPS and virtual users are enabled, the level of security of your vsftpd 
server is increased: encrypted passwords, with passwords that are not used on the system, and users 
that can't access directly to their home directory (if you want). 

From: https://www.benscobie.com/fixing-500-oops-vsftpd-refusing-to-run-with-writable-root-inside-chroot/

For the standard vsFTPd build (vsftpd):

allow_writeable_chroot=YES

For the extended vsFTPd build (vsftpd-ext):

allow_writable_chroot=YES