vmstat - Report virtual memory statistics


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


vmstat reports information about processes, memory, paging, block IO, traps, and cpu activity.

The first report produced gives averages since the last reboot. Additional reports give information on a sampling period of length delay. The process and memory reports are instantaneous in either case.


The -a switch displays active/inactive memory, given a 2.5.41 kernel or better.

The -f switch displays the number of forks since boot. This includes the fork, vfork, and clone system calls, and is equivalent to the total number of tasks created. Each process is represented by one or more tasks, depending on thread usage. This display does not repeat.

The -m displays slabinfo.

The -n switch causes the header to be displayed only once rather than periodically.

The -s switch displays a table of various event counters and memory statistics. This display does not repeat.

delay is the delay between updates in seconds. If no delay is specified, only one report is printed with the average values since boot.

count is the number of updates. If no count is specified and delay is defined, count defaults to infinity.

The -d reports disk statistics (2.5.70 or above required)

The -p followed by some partition name for detailed statistics (2.5.70 or above required)

The -S followed by k or K or m or M switches outputs between 1000, 1024, 1000000, or 1048576 bytes

The -V switch results in displaying version information.


Procs r: The number of processes waiting for run time. b: The number of processes in uninterruptible sleep.

Memory swpd: the amount of virtual memory used. free: the amount of idle memory. buff: the amount of memory used as buffers. cache: the amount of memory used as cache. inact: the amount of inactive memory. (-a option) active: the amount of active memory. (-a option)

Swap si: Amount of memory swapped in from disk (/s). so: Amount of memory swapped to disk (/s).

IO bi: Blocks received from a block device (blocks/s). bo: Blocks sent to a block device (blocks/s).

System in: The number of interrupts per second, including the clock. cs: The number of context switches per second.

CPU These are percentages of total CPU time. us: Time spent running non-kernel code. (user time, including nice time) sy: Time spent running kernel code. (system time) id: Time spent idle. Prior to Linux 2.5.41, this includes IO-wait time. wa: Time spent waiting for IO. Prior to Linux 2.5.41, included in idle. st: Time stolen from a virtual machine. Prior to Linux 2.6.11, unknown.


Reads total: Total reads completed successfully merged: grouped reads (resulting in one I/O) sectors: Sectors read successfully ms: milliseconds spent reading

Writes total: Total writes completed successfully merged: grouped writes (resulting in one I/O) sectors: Sectors written successfully ms: milliseconds spent writing

IO cur: I/O in progress s: seconds spent for I/O


reads: Total number of reads issued to this partition read sectors: Total read sectors for partition writes : Total number of writes issued to this partition requested writes: Total number of write requests made for partition


cache: Cache name num: Number of currently active objects total: Total number of available objects size: Size of each object pages: Number of pages with at least one active object totpages: Total number of allocated pages pslab: Number of pages per slab


vmstat does not require special permissions.

These reports are intended to help identify system bottlenecks. Linux vmstat does not count itself as a running process.

All linux blocks are currently 1024 bytes. Old kernels may report blocks as 512 bytes, 2048 bytes, or 4096 bytes.

Since procps 3.1.9, vmstat lets you choose units (k, K, m, M) default is K (1024 bytes) in the default mode

vmstat uses slabinfo 1.1 FIXME


/proc/meminfo /proc/stat /proc/*/stat


iostat(1), sar(1), mpstat(1), ps(1), top(1), free(1)


Does not tabulate the block io per device or count the number of system calls.


Written by Henry Ware <>. Fabian Frédérick <> (diskstat, slab, partitions...)

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