If you're using a home PC or Linux-based school-issued computers for students, it's easy to create a filtering policy that will be applied to selected users of this computer (children), without an impact for system services and other users (teachers, parents).
Here are the steps for setting up SafeDNS on a computer in this case:
Make sure that in the /etc/resolv.conf file your ISP's DNS or any other DNS (other than SafeDNS DNS addresses) is specified .
In your SafeDNS account, bind your external IP address in your Service Dashboard and associate it with a filtering profile.
In the iptables, write the rules for redirecting the traffic of a certain computer to the DNS server address of SafeDNS
Username is the name of the corresponding user of the computer.
To save the Iptables rules after restarting the computer, run the command.
Similarly, you can create rules for a group of users, if there is such a group for whom the internet should be filtered. In this case, the key will be changing from "uid-owner" to "gid-owner" with a clarification indicating the name of the user group.