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By default, htop shows colored status bars for processors, memory, and swap. From left to right, the bars are colored green, blue, yellow, and red depending on some thresholds.

What does it mean when the Memory bar has a small level of green and blue, and almost all the remainder is yellow? The swap bar is empty. The color settings for htop are "default".

htop screenshot

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Hitting F1 or h will show you the key. But for reference, the default colors are:

CPU:

  • Blue = Low priority threads
  • Green = Normal priority threads
  • Red = Kernel threads

Memory:

  • Green = Used memory
  • Blue = Buffers
  • Yellow/Orange = Cache

There are a couple of different color-schemes available, you can see them through hitting F2.

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    What does orange mean in the CPU bars? Most of my CPU bars are filled with orange, but it doesn't say what it means in the key. May 13 '12 at 19:27
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    @EtiennePerot you are right. There are some more colors. See my answer ;).
    – jjmontes
    Nov 16 '12 at 9:26
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    Yes, it's a good thing. See linuxatemyram.com for a good understanding. May 10 '13 at 19:08
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    Your answer is not totally right about the red color. It's not kernel threads but time spent in kernel code by any priority user threads and time given to kernel threads which spend all their time in kernel code. Jul 2 '14 at 14:11
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I couldn't find this documented elsewhere. Looking into the code:

There are two modes for CPU metrics reporting: the default one, and a "detailed CPU time" which can be enabled from the Setup screen (Display Options / Detailed CPU time). All of them show the percentage of time spent in different processes:

Default mode

  • Blue: low priority processes (nice > 0)
  • Green: normal (user) processes
  • Red: kernel time (kernel, iowait, irqs...)
  • Orange: virt time (steal time + guest time)

Detailed mode

  • Blue: low priority threads (nice > 0)
  • Green: normal (user) processes
  • Red: system processes
  • Orange: IRQ time
  • Magenta: Soft IRQ time
  • Grey: IO Wait time
  • Cyan: Steal time
  • Cyan: Guest time

Memory meters are more straightforward:

  • Green: Used memory pages
  • Blue: Buffer pages
  • Orange: Cache pages
  • Grey: Free (unused)

Note: Info obtained from htop source code at https://github.com/hishamhm/htop/blob/master/CPUMeter.c .

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    press F1 for help.
    – tgies
    Mar 20 '13 at 21:53
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    @tgies - the help page contains something different to this.
    – UpTheCreek
    Dec 8 '15 at 12:15
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    If you put the CPU bars into "detailed" mode then press F1 and this info shows properly.
    – joshperry
    Aug 10 '16 at 18:58
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    If, like me, you see this orange CPU-bars on an Amazon EC instance (aug 2016), most likely your CPU is throttled because your so called "CPU credits" are spent.
    – berkes
    Aug 18 '16 at 8:11
  • Wait so in your answer under 'memory meters' orange is for cache pages, in sysadmin1138's answer under the same it says yellow/orange is for cache pages. Does the code mention anything about the yellow?
    – projectdp
    Mar 26 '17 at 13:20
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There are several different colors for each of the bars, except the Swap bar. Here are the color keys used inside of htop:

enter image description here

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  • The memory bar also has gray, that seems to mean 'available' or 'unused'.
    – Luc
    Feb 19 at 15:01

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