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Abhishek Pathak
Abhishek Pathak

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whatis htop

#tooling #monitoring #cli #linux

This is one of the tools that I use on a daily basis, and though sometimes I have to Google what these columns mean…
So I thought of creating some notes, but then I am here writing this blog with the help of ~AI, funny :), but it is what it is.
I won’t be going into minor things, as you are smart enough for that…

Headers

PID

  • ID of the process, like a unique identifier.

USER

  • Which user started the process.
  • root – system-level
  • daemon, syslog, etc – service users

PRI

  • Priority.
  • Lower number = higher priority.
  • Kernel decides who gets CPU time first.

NI

  • Nice value.
  • User-assigned priority tweak.
  • Range: -20 (very important) to +19 (not so much).
  • This exists to help us give priority to the process.

VIRT

  • Virtual Memory.
  • Total memory the process can use.
  • Includes swapped memory, shared libs, etc.
  • In the image above, the numbers are in KB (kilobytes).

RES

  • Resident Memory.
  • Actual RAM being used right now.
  • This is the important one.
  • In the image above, the numbers are in KB (kilobytes).

SHR

  • Shared Memory.

  • Memory shared with other processes:

    • Shared libs
    • Common system libs

  • In the image above, the numbers are in KB (kilobytes).

    So this means XX KB of the process’s memory can be shared with others.

S

  • What the process is doing now:

    • S → Sleeping
    • R → Running
    • D → Uninterruptible sleep
    • Z → Zombie

  • We mostly see S because most processes wait for input.

CPU%

  • How much of the CPU the process is using right now.

MEM%

  • How much RAM it uses relative to total system RAM.

TIME+

  • Total CPU time a process has consumed since it started.

Command

  • The actual program that launched the process.

Why do we have different colors in the USER column?

Each has a story...

  1. Green

    • Normal user processes
    • Custom Python scripts, CLI scripts, etc.

  2. Blue

    • Low-priority processes

  3. Red/Orange

    • Kernel threads / High-priority tasks

  4. Cyan / Light Blue

    • Threads inside a process (e.g., Python worker threads)

  5. Purple

    • System daemons

  6. Bold Green

    • Running processes

  7. Dark Gray / Dim

    • Idle or sleeping processes taking almost 0 CPU

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