Why is the www-data user missing?

Question

linux

I install daloRADIUS according to this instruction , I reached the Setting Permissions item

sudo chown www-data:www-data /var/www/daloradius -R

If you run this command, an error occurs:
chown: invalid user: ‘www-data:www-data’

Answer 1

If it is centos, then there is an apache user.

Answer 2

Install apache and it will add user www-data