vmstat (Virtual Memory Stats) reports virtual memory statistics.
- how much virtual memory there is,
- how much is free and paging activity.
Most important, you can observe page-ins and page-outs as they happen.
Using this resource monitor, it is possible to get an overview of process, memory, swap, I/O, system, and CPU activity.
The process-related fields are:
- r — The number of runnable processes waiting for access to the CPU
- b — The number of processes in an uninterruptible sleep state
- w — The number of processes swapped out, but runnable
The memory-related fields are:
- swpd — The amount of virtual memory used
- free — The amount of free memory
- buff — The amount of memory used for buffers
- cache — The amount of memory used as page cache
The swap-related fields are:
- si — The amount of memory swapped in from disk
- so — The amount of memory swapped out to disk
The I/O-related fields are:
- bi — Blocks sent to a block device
- bo— Blocks received from a block device
The system-related fields are:
- in — The number of interrupts per second
- cs — The number of context switches per second
The CPU-related fields are:
- us — The percentage of the time the CPU ran user-level code
- sy — The percentage of the time the CPU ran system-level code
- id — The percentage of the time the CPU was idle