===== vsftpd =====
<code bash>
apt install vsftpd -y
useradd ftpuser
passwd ftpuser
echo "ftpuser" | tee -a /etc/vsftpd.userlist
</code>

<WRAP round info 100%>
It is not advisable to use FTP without TLS/SSL/FTPS over the internet because the FTP protocol does not encrypt passwords. If you do need to transfer files over FTP, consider the use of virtual users (same system users but with non system passwords) or TLS/SSL/FTPS.
</WRAP>

/etc/vsftpd.conf
<code bash>
userlist_enable=YES
userlist_file=/etc/vsftpd.userlist
userlist_deny=NO
</code>

https://security.appspot.com/vsftpd/vsftpd_conf.html\\
https://www.digitalocean.com/community/tutorials/how-to-set-up-vsftpd-for-a-user-s-directory-on-ubuntu-16-04\\
https://ubuntuforums.org/showthread.php?t=518293