Kelfitas

sudo su
apt-get install -y autoconf automake libtool nasm make pkg-config
cd /tmp
wget https://github.com/mozilla/mozjpeg/releases/download/v3.1/mozjpeg-3.1-release-source.tar.gz
tar -xvf mozjpeg-3.1-release-source.tar.gz
cd mozjpeg
autoreconf -fiv
mkdir build && cd build
sh ../configure
make install

ipbastola

Safest way to clean up boot partition - Ubuntu 14.04LTS-x64, Ubuntu 16.04LTS-x64

Reference

Case I: if /boot is not 100% full and apt is working

1. Check the current kernel version

$ uname -r