htop screenshot

For the CPU cores, I think that blue means nice, green normal CPU use and red I/O. But I'm not sure and I haven't found a definite answer.

Then there are the colors for memory. What do green, blue and yellow mean there?

  • 4
    I lack the reputation credits to flag this as duplicate, but see the answer at serverfault.com/questions/180711/…, which is a copy of your question and has been answered.
    – Caleb Xu
    Commented Jan 8, 2014 at 4:04
  • 2
    @CalebXu You cannot flag it as a duplicate of a question on another site, but you can post an actual answer here, linking to it.
    – slhck
    Commented Jan 8, 2014 at 8:08

3 Answers 3


Press h inside htop for quick help.


Blue      : Low-priority threads
Green     : Normal priority threads
Red       : Kernel threads
Turquoise : Virtualization threads


Green         : Used memory
Blue          : Buffers
Yellow/Orange : Cache
  • 16
    For anyone wondering what's meant with cache
    – Abdull
    Commented Oct 21, 2016 at 16:56
  • Why is the kernel CPU on the right? Wouldn't it make sense to put it on the left? Commented Feb 5, 2018 at 19:45
  • 1
    @AaronFranke, because your processes are expected to primarily use User CPU. Kernel CPU is when your process calls a kernel function which should use a lot less time in %. Commented Oct 28, 2019 at 0:40

Also, in the list of processes, there are some that appear in Green. The black ones are main processes and the Green ones are threads. In my example below, I'm running a repair on a Cassandra node and as we can see most entries are threads.

enter image description here


Specific to AWS, yellow bars can mean your virtual CPUs are being throttled because they've gone past burstable limit (AWS Burstable Link). This is common with AWS t2 instances.

htop cpus

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