Htop is may favourite tool for monitoring the processes and current CPU utilization on Linux machines, but often I forget what all the different colours mean, so here's a quick review.

Default Basic Setup

CPU Colours

  • Blue - low prioiry threads
  • Green - normal (user) threads
  • Red - kernel threads
  • Orange - Virtualization time (steal time + guest time)

Memory Colours

  • Green - "normal" used memory
  • Blue - buffers
  • Yellow/Orange - Cache

Detailed Setup

  • Blue - low prioiry threads
  • Green - normal (user) threads
  • Red - kernel threads
  • Yellow - disk I/O
  • Orange - Interrupt Request time (IRQ)
  • Magenta - Soft IRQ time
  • Grey - IO Wait time
  • Cyan - Steal time


  • Buffers and Cache
    • Buffers represent how much portion of RAM is dedicated to cache disk block. Cached is similar like "Buffers", only this time it caches pages from file reading.[source]
  • Steal Time
    • The percentage of time a virtual CPU waits for a real CPU while the hypervisor is servicing another virtual processor. [source]
    • This is something to look out for if you deploy to a virtual environment such as Amazon EC2, Rackspace, or Digital Ocean

    • [ 86.6% of CPU stolen during an update of a micro EC2 instance ]

  • Software Interrupt Request (SIRQ)
    • Used often by device drivers to do further processing of something outside of the hardware interrupt handler.[source]
  • Guest Time
    • time spent running a virtual CPU for a guest operating system. [ source ]

Turning On Detailed Colors

Htop does not show the detailed setup by default. To enable this, press F2. Then press the down key once to highlight "Display options". Then press the right key and then navigate down to "Detailed CPU time ..." before pressing the spacebar.


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