Busybox

Start with busybox in Grub

init=/bin/busybox

Use it:

busybox-static ls # ou dmesg ou autre commande

Like it states in –help output: create some symlinks to it:

mkdir xxx
cd xxx
for f in $(/usr/bin/busybox-static --list); do \
ln -s /usr/bin/busybox-static $f; done
./uname
Linux

FWIW: one could also build the ‘coreutils’ package to have an all-in-one program which acts the same:

./configure --help
...
--enable-single-binary=shebangs|symlinks
                        Compile all the tools in a single binary, reducing
                        the overall size. When compiled this way, shebangs
                        (default when enabled) or symlinks are installed for
                        each tool that points to the single binary.