IOSTAT(8) System Manager's Manual IOSTAT(8)

iostat — report I/O statistics

iostat [-CUdKIoT?] [-c count] [-n devs] [-w wait] [drives]

The iostat utility displays kernel I/O statistics on terminal, device and cpu operations. The first statistics that are printed are averaged over the system uptime. To get information about the current activity, a suitable wait time should be specified, so that the subsequent sets of printed statistics will be averaged over that time.

The options are as follows:

Display a usage statement and exit.
Repeat the display count times. If no wait interval is specified, the default is 1 second.
Display CPU statistics. This is on by default, unless -d is specified.
Display only device statistics. If this flag is turned on, only device statistics will be displayed, unless -C or -U or -T is also specified to enable the display of CPU, load average or TTY statistics.
Display total statistics for a given time period, rather than average statistics for each second during that time period.
In the blocks transferred display (-o), display block count in kilobytes rather then the device native block size.
Display up to devs number of devices. The iostat utility will display fewer devices if there are not devs devices present.
Display old-style iostat device statistics. Sectors per second, transfers per second, and milliseconds per seek are displayed. If -I is specified, total blocks/sectors, total transfers, and milliseconds per seek are displayed.
Display TTY statistics. This is on by default, unless -d is specified.
Display system load averages. This is on by default, unless -d is specified.
Pause wait seconds between each display. If no repeat count is specified, the default is infinity.

The iostat utility displays its information in the following format:

tty
tin
characters read from terminals
tout
characters written to terminals
devices
Device operations. The header of the field is the device name and unit number. The iostat utility will display as many devices as will fit in a standard 80 column screen, or the maximum number of devices in the system, whichever is smaller. If -n is specified on the command line, iostat will display the smaller of the requested number of devices, and the maximum number of devices in the system. To force iostat to display specific drives, their names may be supplied on the command line. The iostat utility will not display more devices than will fit in an 80 column screen, unless the -n argument is given on the command line to specify a maximum number of devices to display, or the list of specified devices exceeds 80 columns. If fewer devices are specified on the command line than will fit in an 80 column screen, iostat will show only the specified devices.

The standard iostat device display shows the following statistics:

KB/t
kilobytes per transfer
tps
transfers per second
MB/s
megabytes per second

The standard iostat device display, with the -I flag specified, shows the following statistics:

KB/t
kilobytes per transfer
xfrs
total number of transfers
MB
total number of megabytes transferred

The old-style iostat display (using -o) shows the following statistics:

sps
sectors transferred per second
tps
transfers per second
msps
average milliseconds per transaction

The old-style iostat display, with the -I flag specified, shows the following statistics:

blk
total blocks/sectors transferred
xfr
total transfers
msps
average milliseconds per transaction
cpu
us
% of cpu time in user mode
sy
% of cpu time in system mode
id
% of cpu time in idle mode

iostat -w 1 disk0 disk2

Display statistics for the first and third disk devices device every second ad infinitum.

iostat -c 2

Display the statistics for the first four devices in the system twice, with a one second display interval.

iostat -Iw 3

Display total statistics every three seconds ad infinitum.

iostat -odICTw 2 -c 9

Display total statistics using the old-style output format 9 times, with a two second interval between each measurement/display. The -d flag generally disables the TTY and CPU displays, but since the -T and -C flags are given, the TTY and CPU displays will be displayed.

netstat(1), nfsstat(1), ps(1), top(1), vm_stat(1)

The sections starting with ``Interpreting system activity'' in Installing and Operating 4.3BSD.

This version of iostat first appeared in FreeBSD 3.0.

May 22, 2015 macOS 15.2