file: /proc/sys/net/ipv4/ip_unprivileged_port_start
variable: net.ipv4.ip_unprivileged_port_start
Official reference

This is a per-namespace sysctl. It defines the first unprivileged port in the network namespace. Privileged ports require root or CAP_NET_BIND_SERVICE in order to bind to them. To disable all privileged ports, set this to 0. It may not overlap with the ip_local_reserved_ports range.

Default: 1024