systemd: allow normal process to bind to privileged port
Sometimes services are started by systemd with already dropped
privileges, for example
inspircd.service
starts as irc user.
Such services cannot bind to priliged ports (< 1024) usually - in this
case I needed it to listen to port 443 though (additionally to some high
port) to allow users behind special firewall configurations to connect
to the server.
The solution is to add the following to the service (for example by
running systemctl edit inspircd.service):