top is a simple tool that doesn't require any special kernel options or symbol tables. There is a basic version in BusyBox, and a more functional version in the
procps package which is available in the Yocto Project and Buildroot. You may also want to consider using
htop which is functionally similar to
top but has a nicer user interface (some people think).
To begin with, focus on the summary line of
top, which is the second line if you are using BusyBox and the third line if using
top. Here is an example, using BusyBox
Mem: 57044K used, 446172K free, 40K shrd, 3352K buff, 34452K cached CPU: 58% usr 4% sys 0% nic 0% idle 37% io 0% irq 0% sirq Load average: 0.24 0.06 0.02 2/51 105 PID PPID USER STAT VSZ %VSZ %CPU ...