---
name: "iostat"
section: "8"
platform: "openbsd"
package: "man"
version: "8.0-current-20261101"
release: "OpenBSD 8.0-current (2026-11-01)"
platforms: ["freebsd", "openbsd", "macos"]
url: "https://new.carta.tech/iostat/8"
---

# iostat(8)

report I/O statistics

## NAME

**iostat** – report I/O statistics

## SYNOPSIS

**iostat** \[**-CDdIT**\] \[**-c** *count*\] \[**-M** *core*\] \[**-N** *system*\] \[**-w** *wait*\] \[*drives*\]

## DESCRIPTION

**iostat** displays kernel I/O statistics on terminal, disk and CPU operations. By default, **iostat** displays one line of statistics averaged over the machine's run time. The **-I** option causes **iostat** to print raw, unaveraged values.

The options are as follows:

- **-C**

  Show CPU statistics. This is enabled by default unless the **-D**, **-d**, or **-T** flags are used.

- **-c** *count*

  Repeat the display *count* times. Unless the **-I** flag is in effect, the first display is for the time since a reboot and each subsequent report is for the time period since the last display. Unless overridden by the **-w** option, the wait interval between lines is 1 second.

- **-D**

  Show alternate disk statistics. Displays kilobytes transferred, number of transfers, and time spent in transfers. Use of this flag disables the default display.

- **-d**

  Show disk statistics. This is the default. Displays kilobytes per transfer, number of transfers, and megabytes transferred. Use of this flag disables display of CPU and tty statistics.

- **-I**

  Show the running total values, rather than an average.

- **-M** *core*

  Extract values associated with the name list from the specified *core* instead of the default */dev/mem*.

- **-N** *system*

  Extract the name list from the specified *system* instead of the default “*/bsd*”.

- **-T**

  Show tty statistics. This is enabled by default unless the **-C**, **-D**, or **-d** flags are used.

- **-w** *wait*

  Pause *wait* seconds between each display. Unless a *count* is specified via the **-c** option, **iostat** will display output until it is interrupted.

**iostat** displays its information in the following format:

- tty

  - tin

    characters read from terminals

  - tout

    characters written to terminals

- disks

  Disk operations. The header of the field is the disk name and unit number. If more than four disk drives are configured in the system, **iostat** displays only the first four drives. To force **iostat** to display specific drives, their names may be supplied on the command line.

  - KB/t

    Kilobytes transferred per disk transfer

  - t/s

    Transfers per second

  - MB/s

    Megabytes transferred per second

    The alternate display format, selected with **-D**, presents the following values:

    - KB

      Kilobytes transferred

    - xfr

      Disk transfers

    - time

      Seconds spent in disk activity

- cpu

  - us

    % of CPU time in user mode

  - ni

    % of CPU time in user mode running niced processes

  - sy

    % of CPU time in system mode

  - sp

    % of CPU time spent spinning

  - in

    % of CPU time processing interrupts

  - id

    % of CPU time in idle mode

## FILES

- */bsd*

  default kernel namelist

- */dev/mem*

  default memory file

## SEE ALSO

[fstat(1)](/fstat/1.md), [netstat(1)](/netstat/1.md), [nfsstat(1)](/nfsstat/1.md), [ps(1)](/ps/1.md), [systat(1)](/systat/1.md), [top(1)](/top/1.md), [pstat(8)](/pstat/8.md), [vmstat(8)](/vmstat/8.md)

The sections starting with “Interpreting system activity” in