sudo apt-get install bcmwl-kernel-source
Reading package lists... Done
Building dependency tree
Reading state information... Done
The following packages were automatically installed and are no longer required:
  gtk3-engines-unico libatkmm-1.6-1 libcairomm-1.0-1 libglibmm-2.4-1c2a
  libgrip0 libpangomm-1.4-1 libsigc++-2.0-0c2a libtimezonemap1
  linux-headers-3.16.0-34 linux-headers-3.16.0-34-generic
  linux-image-3.16.0-34-generic linux-image-extra-3.16.0-34-generic
  linux-signed-image-3.16.0-34-generic
Use 'apt-get autoremove' to remove them.
The following NEW packages will be installed:
  bcmwl-kernel-source
0 upgraded, 1 newly installed, 0 to remove and 6 not upgraded.
Need to get 0 B/1,518 kB of archives.
After this operation, 8,042 kB of additional disk space will be used.
Selecting previously unselected package bcmwl-kernel-source.
(Reading database ... 192945 files and directories currently installed.)
Preparing to unpack .../bcmwl-kernel-source_6.30.223.248+bdcom-1longsleep0_amd64.deb ...
Unpacking bcmwl-kernel-source (6.30.223.248+bdcom-1longsleep0) ...
Setting up bcmwl-kernel-source (6.30.223.248+bdcom-1longsleep0) ...
Loading new bcmwl-6.30.223.248+bdcom DKMS files...
Building only for 4.0.0-040000-lowlatency
Building for architecture x86_64
Module build for the currently running kernel was skipped since the
kernel source for this kernel does not seem to be installed.
modprobe: FATAL: Module wl not found.
update-initramfs: deferring update (trigger activated)
Processing triggers for initramfs-tools (0.103ubuntu4.2) ...
update-initramfs: Generating /boot/initrd.img-4.0.0-040000-lowlatency