# First step is:
sudo apt-get install vsftpd

# Edit /etc/vsftpd.conf. and edit/add following lines
anonymous_enable=NO
local_enable=YES
write_enable=YES
local_umask=0002
anon_upload_enable=YES
anon_mkdir_write_enable=YES
file_open_mode=0777

# Other Following commands
sudo adduser ftpuser
sudo usermod -d /var/www -m ftpuser
sudo usermod -a -G www-data ftpuser
sudo usermod -a -G www-data ftpuser
sudo chgrp -R www-data /var/www
sudo chmod -R g+w /var/www
sudo find /var/www -type d -exec chmod 2775 {} \;
sudo find /var/www -type f -exec chmod ug+rw {} \;

# Reference:
FTP user create
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