When I modify some ipv4 config for system I got an error like this: sysctl: setting key "net.ipv4.tcp_congestion_control": No such file or directory, so I followed this post to build a kernel module for ubuntu 14.04

The net/ipv4 hybla Makefile(bad script format in original post):

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# Makefile for tcp_hybla.ko
obj-m := tcp_hybla.o
KDIR := /home/dejavu/linux-4.1.5
PWD := $(shell pwd)
default:
  $(MAKE) -C $(KDIR) SUBDIRS=$(PWD) modules

I also got a warning during build modules: No X.509 certificates found, but it doesn’t matter I think, I can build the tcp_hybla.ko and load in kernel.