Like iostat, vmstat is part of the sysstat package. You can run the command by itself:
vmstat
and get a display of active and inactive memory:
procs -----------memory---------- ---swap-- -----io---- --system-- ----cpu----
r b swpd free buff cache si so bi bo in cs us sy id wa
0 0 0 1826368 57028 102352 0 0 1 1 251 6 0 0 100 0
Notice that you’re given sections for memory (RAM), swap (virtual memory on disk), I/O, in-memory and in-swap system memory, and CPU usage. Now run the command:
vmstat 1 5
for five reports at one-second intervals:
procs -----------memory---------- ---swap-- -----io---- --system-- ----cpu----
r b swpd free buff cache si so bi bo in cs us sy id wa
0 0 0 1826368 57028 102352 0 0 1 1 251 6 0 0 100 0
0 0 0 1826368 57028 102352 0 0 0 0 1008 13 0 0 100 0
0 0 0 1826368 57028 102352 0 0 0 0 1004 13 0 0 100 0
0 0 0 1826368 57036 102344 0 0 0 60 1007 25 0 0 100 0
0 0 0 1826368 57036 102344 0 0 0 0 1004 13 0 0 100 0
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procs
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memory
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swap
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io
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system
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cpu
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r
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b
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swpd
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free
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buff
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cache
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si
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so
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bi
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bo
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in
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cs
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us
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sy
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id
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wa
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| # processes waiting to be run | # sleeping processes | used swap in K | free RAM | RAM used for buffers in K | RAM used as system cache | K/s swapped in | K/s swapped out | blocks/s sent to block devices | blocks/s received from block devices | interrupts/s sent to CPU | context changes/s sent to CPU | CPU user time | CPU system time | CPU idle time | CPU wait time for I/O |
If you don’t have enough swap space, you’ll see it here as excessive swap-in and swap-out.
If you don’t have enough RAM, you’ll see too little free memory.
If you’ve got too slow a CPU, the last column will show you too much waiting going on.
And if system processes are hogging memory, you’ll see too little free memory.
A related utility is the free command. It displays total RAM and swap memory in Kilobytes (K), and the amount actually in use.
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total
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used
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free
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shared
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buffers |
cached
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| Mem: | total RAM | RAM in use | free RAM | shared memory | requests from hardware devices | reserved by the kernel |
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-/+ buffers/cache:
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RAM minus buffers
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RAM minus cache
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| Swap: | Swap file/partition size | Amount of swap used | Free swap space |