Question

19

What is "cached" in the top command?

rated 0 times [ 19] [ 0] / answers: 1 / hits: 95915 / 3 Years ago, tue, july 27, 2021, 6:46:12

When running top, I get:

top - 09:10:52 up 18:37,  1 user,  load average: 1.56, 1.33, 1.15

Tasks:  39 total,   1 running,  38 sleeping,   0 stopped,   0 zombie

Cpu(s):  0.1%us,  0.6%sy,  1.0%ni, 92.5%id,  5.8%wa,  0.0%hi,  0.0%si,  0.0%st

Mem:   4194304k total,  3045460k used,  1148844k free,        0k buffers

Swap:        0k total,        0k used,        0k free,  2256128k cached

See the part: 2256128k cached? What exactly does that mean?

I am comparing two VPS from two provider, this one always has a large amount there (70% of the used memory) and the other VPS provider always shows 0.

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edseager

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2 Years ago

answered 3 Years ago alkeake · Accepted Answer

That number before cached is the amount of physical memory that is being used by cache buffers for your filesystems.

It's not actually related to SWAP, despite being on the "Swap:" line.

To verify my answer with a little experiment try the following:

Run top and note the value of 'cached'. Now run

dd if=/dev/zero of=~/trick bs=1M count=128

if you run top again you'll notice that 'cached' has grown by 128M

Now remove the file

rm ~/trick

Run top again and you'll see 'cached' has dropped by 128M

So for Mem:

total = used + free and

used = <all apps> + buffers + cached

(where buffers is basically metadata for the cached). A bit confusing of a UI.