iostat8

Usage

Overview

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.

Not on FreeBSD or macOS.

-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.

Not on macOS.

-N system

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

Not on macOS.

-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