Understand more about vmstat

Updated: 22 October 2026 · Applies to: procps-ng vmstat, any Linux distribution

vmstat (virtual memory statistics) reports a summary of memory, processes, interrupts, paging and block I/O. Give it a delay (in seconds) to sample system activity repeatedly instead of once.

vmstat [-a] [-n] [-S unit] [delay [count]]
vmstat [-s] [-n] [-S unit]
vmstat [-m] [-n] [delay [count]]
vmstat [-d] [-n] [delay [count]]
vmstat [-p disk_partition] [-n] [delay [count]]
vmstat [-f]
vmstat [-V]

Options

• -a: show active and inactive memory.
• -f: show the number of forks since boot (fork, vfork and clone calls combined). Does not repeat.
• -m: show slab info.
• -n: print the header once instead of before every sample.
• -s: show a table of event counters and memory statistics. Does not repeat.
• -d: show disk statistics.
• -p partition: show detailed statistics for one partition.
• -S k|K|m|M: display units in 1000, 1024, 1,000,000 or 1,048,576 bytes.
• -V: show version information.
• delay: seconds between updates. Without it, one report is printed using the average since boot.
• count: number of updates to print. If delay is set but count is not, it repeats indefinitely.

Field descriptions

Procs

• r: processes waiting for run time.
• b: processes in uninterruptible sleep.

Both r and b are normally close to 0. A consistently high value means the system does not have enough CPU, memory or I/O bandwidth.

Memory

• swpd: virtual memory used.
• free: idle memory.
• buff: memory used as buffers.
• cache: memory used as cache.
• inact: inactive memory (with -a).
• active: active memory (with -a).

Swap

• si: memory swapped in from disk, per second.
• so: memory swapped out to disk, per second.

A swpd value that stays high and keeps changing means the system is running short of memory.

IO

• bi: blocks received from a block device, per second.
• bo: blocks sent to a block device, per second.

System

• in: interrupts per second, including the clock.
• cs: context switches per second.

CPU (percentage of total CPU time)

• us: time running non-kernel (user) code.
• sy: time running kernel code.
• id: time idle.
• wa: time waiting for I/O.
• st: time stolen by the hypervisor, on a virtual machine.

Disk mode (-d)

• reads/writes: total, merged, sectors, and milliseconds spent.
• io: current I/O in progress, and seconds spent on I/O.