FROM busybox
RUN top

FROM busybox

For some POSIX commands it makes no sense to run them in a Docker container because they are bound to the host or are otherwise dangerous (like ´shutdown´, ´service´, ´ps´, ´free´, ´top´, ´kill´, ´mount´, ´ifconfig´). Interactive utilities also don't make much sense (´nano´, ´vim´).