Vmstat

The vmstat (virtual memory statistics) is a built-in monitoring utility in Linux.

The command is used to obtain information about memory, system processes, paging, interrupts, block I/O, disk, and CPU scheduling. Users can observe system activity virtually in real-time by specifying a sampling period.

Output meaning

$ vmstat -n 1
procs -----------memory---------- ---swap-- -----io---- -system-- ------cpu-----
 r  b   swpd   free   buff  cache   si   so    bi    bo   in   cs us sy id wa st
 0  0  22116 182900  35548 378464    0    0     4     3    1   30  0  0 100  0  0
 0  0  22116 182904  35548 378480    0    0     0     0    0   44  0  0 100  0  0
 0  0  22116 182904  35548 378480    0    0     0     0    2   41  0  0 100  0  0
 0  0  22116 182904  35548 378480    0    0     0     0    0   49  0  0 100  0  0
 0  0  22116 182904  35548 378480    0    0     0     0    2   45  0  0 100  0  0
 0  0  22116 182904  35548 378480    0    0     0     0    0   46  0  0 100  0  0
 0  0  22116 182892  35556 378472    0    0     0    20    2   64  0  0 99  1  0
 0  0  22116 182896  35556 378480    0    0     0     0    0   44  0  0 100  0  0

Section	Meaning	Notes
procs	r – Active process count. b – Sleeping process count.
memory	swpd – Total virtual memory. The swap space is initially unoccupied. However, the kernel starts using swap space as the system’s physical memory reaches its limit. free – Total free memory. buff – Total memory temporarily used as a data buffer. cache – Total cache memory
swap	si – The rate of swapping-in memory from disk. so – The rate of swapping-out memory to disk.
o	bi – Blocks received from a block device per second. bo – Blocks sent to a block device per second.
system	in – The number of system interrupts. cs – The number of context switches per second.
cpu	us – The percentage of CPU time spent on non-kernel processes. sy – The percentage of CPU time spent on kernel processes. id – The percentage of idle CPU. wa – The percentage of CPU time spent waiting for Input/Output. st – The percentage of CPU time stolen by a virtual machine.	The connection queue length is displayed in the “wa” column, which stands for “wait”. This value represents the number of processes that are waiting for a resource, such as a connection. If the value in the “wa” column is high, it could indicate that the server is experiencing a high load and may be unable to handle additional connections efficiently. In this case, increasing its capacity to handle the load by e.g. upgrading the hardware/network capacity for your website is recommended.