How can I give a user permission to open low port numbers?

Question

If I'm root, how can I give a user permission to open low port numbers ? Or how can I take away the right to open high port numbers from a user ?

Cheers !

Answer 1

You can allow specific programs (not users) to open privileged ports:

setcap 'cap_net_bind_service=+ep' /path/to/executable

As for restricting access to certain ports, see Allow/Deny a user from binding a range of ports.