iostat(8)

NAME

iostat - report I/O statistics

SYNOPSIS

iostat [-CdhKIoT?]  [-c  count]  [-M  core]  [-n  devs]  [-N
system] [-t
       type,if,pass] [-w wait] [drives]

DESCRIPTION

The iostat utility displays kernel I/O statistics on termi

nal, device and
cpu operations. The first statistics that are printed are

averaged over
the system uptime. To get information about the current ac

tivity, a
suitable wait time should be specified, so that the subse

quent sets of
printed statistics will be averaged over that time.

The options are as follows:

-c Repeat the display count times. If no wait interval

is specified,

the default is 1 second.

-C Display CPU statistics. This is on by default, unless

-d is speci

fied.

-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 aver

age statistics for each second during that time peri

od.

-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 dis

play fewer devices if there are not devs devices pre

sent.

-N Extract the name list from the specified system in

stead 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 trans

fers, and milliseconds per seek are displayed.

-t Specify which types of devices to display. There are

three differ

ent 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 de

vices
SCSI Small Computer System Interface de

vices
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 de

vice 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 dis

played in 80
columns, or the maximum number of devices specified by

the user.

-T Display TTY statistics. This is on by default, unless

-d is speci

fied.

-w Pause wait seconds between each display. If no repeat

count is

specified, the default is infinity.

-? 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 de

vice name and
unit number. The iostat utility will display as many

devices as
will fit in a standard 80 column screen, or the maxi

mum 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, un

less 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 old-style iostat display (using -o) shows the fol

lowing statistics:

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

The old-style iostat display, with the -I flag speci

fied, 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 pro

cesses
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

iostat -w 1 da0 da1 cd0

Display statistics for the first two Direct Access devices

and the first
CDROM 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 -t da -t cd -w 1

Display statistics for all CDROM and Direct Access devices

every second
ad infinitum.

iostat -t da,scsi,pass -t cd,scsi,pass

Display statistics once for all SCSI passthrough devices

that provide
access to either Direct Access or CDROM devices.

iostat -h -n 8 -w 1

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

infinitum.

iostat -dh -t da -w 1

Omit the TTY and CPU displays, show devices in order of per

formance and
show only Direct Access devices every second ad infinitum.

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.

SEE ALSO

fstat(1), netstat(1), nfsstat(1), ps(1), systat(1),

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 on

ly cover the
time immediately before the crash.

BSD December 22, 1997

BSD