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

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