NAME

iostat — report I/O statistics

SYNOPSIS

DESCRIPTION

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:

-c

Repeat the display count times. If no repeat count is specified, the default depends on whether -w is specified. With -w the default repeat count is infinity, otherwise it is 1.

-C

Display CPU statistics. This is on by default, unless -d or -x is specified.

-d

Display only device statistics. If this flag is turned on, only device statistics will be displayed, unless -C or -T is also specified to enable the display of CPU or TTY statistics.

-h

Put iostat in ‘top’ mode. In this mode, iostat will show devices in order from highest to lowest bytes per measurement cycle.

-I

Display total statistics for a given time period, rather than average statistics for each second during that time period.

-K

In the blocks transferred display (-o), display block count in kilobytes rather then the device native block size.

-M

Extract values associated with the name list from the specified core instead of the default “/dev/kmem”.

-n

Display up to devs number of devices. The iostat utility will display fewer devices if there are not devs devices present.

-N

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

-o

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.

-t

Specify which types of devices to display. There are three different categories of devices:

device type:

da

Direct Access devices

sa

Sequential Access devices

printer

Printers

proc

Processor devices

worm

Write Once Read Multiple devices

cd

CD devices

scanner

Scanner devices

optical

Optical Memory devices

changer

Medium Changer devices

comm

Communication devices

array

Storage Array devices

enclosure

Enclosure Services devices

floppy

Floppy devices

interface:

IDE

Integrated Drive Electronics devices

SCSI

Small Computer System Interface devices

other

Any other device interface

passthrough:

pass

Passthrough devices

The user must specify at least one device type, and may specify at most one device type from each category. Multiple device types in a single device type statement must be separated by commas.

Any number of -t arguments may be specified on the command line. All -t arguments are ORed together to form a matching expression against which all devices in the system are compared. Any device that fully matches any -t argument will be included in the iostat output, up to the number of devices that can be displayed in 80 columns, or the maximum number of devices specified by the user.

-T

Display TTY statistics. This is on by default, unless -d or -x is specified.

-w

Pause wait seconds between each display. If no wait interval is specified, the default is 1 second.

The iostat command will accept and honor a non-integer number of seconds. Note that the interval only has millisecond granularity. Finer values will be truncated. E.g., “-w1.0001” is the same as “-w1.000”. The interval will also suffer from modifications to kern.hz so your mileage may vary.

-x

Show extended disk statistics. Each disk is displayed on a line of its own with all available statistics. If this flag is turned on, only disk statistics will be displayed, unless -C or -T is also specified to enable the display of CPU or TTY statistics.

-z

If -x is specified, omit lines for devices with no activity.

-?

Display a usage statement and exit.

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. 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 extended iostat device display, with the -x flag specified, shows the following statistics:

r/s

read operations per second

w/s

write operations per second

kr/s

kilobytes read per second

kw/s

kilobytes write per second

qlen

transactions queue length

ms/r

average duration of read transactions, in milliseconds

ms/w

average duration of write transactions, in milliseconds

ms/o

average duration of all other transactions, in milliseconds

ms/t

average duration of all transactions, in milliseconds

%b

% of time the device had one or more outstanding transactions

The extended iostat device display, with the -x and -I flags specified, shows the following statistics:

r/i

read operations per time period

w/i

write operations per time period

kr/i

kilobytes read per time period

kw/i

kilobytes write per time period

qlen

transactions queue length

tsvc_t/i

total duration of transactions per time period, in seconds

sb/i

total time the device had one or more outstanding transactions per time period, in seconds

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

ni

% of cpu time in user mode running niced processes

sy

% of cpu time in system mode

in

% of cpu time in interrupt mode

id

% of cpu time in idle mode

FILES

/boot/kernel/kernel

Default kernel namelist.

/dev/kmem

Default memory file.

EXAMPLES

Display statistics for the first two Direct Access devices and the first CDROM device every second ad infinitum.

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

Display statistics for all CDROM and Direct Access devices every second ad infinitum.

Display statistics once for all SCSI passthrough devices that provide access to either Direct Access or CDROM devices.

Display up to 8 devices with the most I/O every second ad infinitum.

Omit the TTY and CPU displays, show devices in order of performance and show only Direct Access devices every second ad infinitum.

Display total statistics every three seconds ad infinitum.

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.

SEE ALSO

fstat(1), netstat(1), nfsstat(1), ps(1), systat(1), devstat(3), ctlstat(8), gstat(8), pstat(8), vmstat(8)

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

HISTORY

This version of iostat first appeared in FreeBSD 3.0.

AUTHORS

Kenneth Merry <ken@FreeBSD.org>

BUGS

The use of iostat as a debugging tool for crash dumps is probably limited because there is currently no way to get statistics that only cover the time immediately before the crash.