.\"
.\" Copyright (c) 1997 Kenneth D. Merry.
.\" All rights reserved.
.\"
.\" Redistribution and use in source and binary forms, with or without
.\" modification, are permitted provided that the following conditions
.\" are met:
.\" 1. Redistributions of source code must retain the above copyright
.\"    notice, this list of conditions and the following disclaimer.
.\" 2. Redistributions in binary form must reproduce the above copyright
.\"    notice, this list of conditions and the following disclaimer in the
.\"    documentation and/or other materials provided with the distribution.
.\" 3. The name of the author may not be used to endorse or promote products
.\"    derived from this software without specific prior written permission.
.\"
.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
.\" ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
.\" SUCH DAMAGE.
.\"
.\" Copyright (c) 1985, 1991, 1993
.\"	The Regents of the University of California.  All rights reserved.
.\"
.\" Redistribution and use in source and binary forms, with or without
.\" modification, are permitted provided that the following conditions
.\" are met:
.\" 1. Redistributions of source code must retain the above copyright
.\"    notice, this list of conditions and the following disclaimer.
.\" 2. Redistributions in binary form must reproduce the above copyright
.\"    notice, this list of conditions and the following disclaimer in the
.\"    documentation and/or other materials provided with the distribution.
.\" 3. Neither the name of the University nor the names of its contributors
.\"    may be used to endorse or promote products derived from this software
.\"    without specific prior written permission.
.\"
.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
.\" ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
.\" SUCH DAMAGE.
.\"
.\"	@(#)iostat.8	8.1 (Berkeley) 6/6/93
.\"
.Dd August 29, 2023
.Dt IOSTAT 8
.Os
.Sh NAME
.Nm iostat
.Nd report
.Tn I/O
statistics
.Sh SYNOPSIS
.Nm
.Op Fl CdhIKoTxz
.Op Fl c Ar count
.Op Fl M Ar core
.Op Fl n Ar devs
.Op Fl N Ar system
.Oo
.Fl t
.Sm off
.Ar type , if , pass
.Sm on
.Oc
.Op Fl w Ar wait
.Op Ar drives
.Sh DESCRIPTION
The
.Nm
utility displays kernel
.Tn 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.
.Pp
The options are as follows:
.Bl -tag -width flag
.It Fl C
Display CPU statistics.
This is on by default, unless
.Fl d
or
.Fl x
is specified.
.It Fl c
Repeat the display
.Ar count
times.
If no repeat
.Ar count
is specified, the default depends on whether
.Fl w
is specified.
With
.Fl w
the default repeat count is infinity, otherwise it is 1.
.It Fl d
Display only device statistics.
If this flag is turned on, only device statistics will be displayed, unless
.Fl C
or
.Fl T
is also specified to enable the display of CPU or TTY statistics.
.It Fl h
Put
.Nm
in
.Sq top
mode.
In this mode,
.Nm
will show devices in order from highest to lowest bytes
per measurement cycle.
.It Fl I
Display total statistics for a given time period, rather than average
statistics for each second during that time period.
.It Fl K
In the blocks transferred display (-o), display block count in kilobytes rather
then the device native block size.
.It Fl M
Extract values associated with the name list from the specified core
instead of the default
.Dq Pa /dev/kmem .
.It Fl N
Extract the name list from the specified system instead of the default
.Dq Pa /boot/kernel/kernel .
.It Fl n
Display up to
.Ar devs
number of devices.
The
.Nm
utility will display fewer devices if there are not
.Ar devs
devices present.
.It Fl o
Display old-style
.Nm
device statistics.
Sectors per second, transfers per second, and milliseconds per seek are
displayed.
If
.Fl I
is specified, total blocks/sectors, total transfers, and
milliseconds per seek are displayed.
.It Fl T
Display TTY statistics.
This is on by default, unless
.Fl d
or
.Fl x
is specified.
.It Fl t
Specify which types of devices to display.
There are three different categories of devices:
.Pp
.Bl -tag -width indent -compact
.It device type:
.Bl -tag -width 9n -compact
.It da
Direct Access devices
.It sa
Sequential Access devices
.It printer
Printers
.It proc
Processor devices
.It worm
Write Once Read Multiple devices
.It cd
CD devices
.It scanner
Scanner devices
.It optical
Optical Memory devices
.It changer
Medium Changer devices
.It comm
Communication devices
.It array
Storage Array devices
.It enclosure
Enclosure Services devices
.It floppy
Floppy devices
.El
.Pp
.It interface:
.Bl -tag -width 9n -compact
.It IDE
Integrated Drive Electronics devices
.It SCSI
Small Computer System Interface devices
.It other
Any other device interface
.El
.Pp
.It passthrough:
.Bl -tag -width 9n -compact
.It pass
Passthrough devices
.El
.El
.Pp
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.
.Pp
Any number of
.Fl t
arguments may be specified on the command line.
All
.Fl 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
.Fl t
argument will be included in the
.Nm
output, up to the number of devices that can be displayed in
80 columns, or the maximum number of devices specified by the user.
.It Fl w
Pause
.Ar wait
seconds between each display.
If no
.Ar wait
interval is specified, the default is 1 second.
.Pp
The
.Nm
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.,
.Dq Li -w1.0001
is the same as
.Dq Li -w1.000 .
The interval will also suffer from modifications to
.Va kern.hz
so your mileage may vary.
.It Fl 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
.Fl C
or
.Fl T
is also specified to enable the display of CPU or TTY statistics.
.It Fl z
If
.Fl x
is specified, omit lines for devices with no activity.
.El
.Pp
The
.Nm
utility displays its information in the following format:
.Bl -tag -width flag
.It tty
.Bl -tag -width indent -compact
.It tin
characters read from terminals
.It tout
characters written to terminals
.El
.It devices
Device operations.
The header of the field is the device name and unit number.
The
.Nm
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
.Fl n
is specified on the command line,
.Nm
will display the smaller of the
requested number of devices, and the maximum number of devices in the system.
To force
.Nm
to display specific drives, their names may be supplied on the command
line.
The
.Nm
utility
will not display more devices than will fit in an 80 column screen, unless
the
.Fl 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,
.Nm
will show only the specified devices.
.Pp
The standard
.Nm
device display shows the following statistics:
.Pp
.Bl -tag -width indent -compact
.It KB/t
kilobytes per transfer
.It tps
transfers per second
.It MB/s
megabytes per second
.El
.Pp
The standard
.Nm
device display, with the
.Fl I
flag specified, shows the following statistics:
.Pp
.Bl -tag -width indent -compact
.It KB/t
kilobytes per transfer
.It xfrs
total number of transfers
.It MB
total number of megabytes transferred
.El
.Pp
The extended
.Nm
device display, with the
.Fl x
flag specified, shows the following statistics:
.Pp
.Bl -tag -width indent -compact
.It r/s
read operations per second
.It w/s
write operations per second
.It kr/s
kilobytes read per second
.It kw/s
kilobytes write per second
.It qlen
transactions queue length
.It ms/r
average duration of read transactions, in milliseconds
.It ms/w
average duration of write transactions, in milliseconds
.It ms/o
average duration of all other transactions, in milliseconds
.It ms/t
average duration of all transactions, in milliseconds
.It %b
% of time the device had one or more outstanding transactions
.El
.Pp
The extended
.Nm
device display, with the
.Fl x
and
.Fl I
flags specified, shows the following statistics:
.Pp
.Bl -tag -width indent -compact
.It r/i
read operations per time period
.It w/i
write operations per time period
.It kr/i
kilobytes read per time period
.It kw/i
kilobytes write per time period
.It qlen
transactions queue length
.It tsvc_t/i
total duration of transactions per time period, in seconds
.It sb/i
total time the device had one or more outstanding transactions per
time period, in seconds
.El
.Pp
The old-style
.Nm
display (using
.Fl o )
shows the following statistics:
.Pp
.Bl -tag -width indent -compact
.It sps
sectors transferred per second
.It tps
transfers per second
.It msps
average milliseconds per transaction
.El
.Pp
The old-style
.Nm
display, with the
.Fl I
flag specified, shows the following statistics:
.Pp
.Bl -tag -width indent -compact
.It blk
total blocks/sectors transferred
.It xfr
total transfers
.It msps
average milliseconds per transaction
.El
.It cpu
.Bl -tag -width indent -compact
.It \&us
% of cpu time in user mode
.It \&ni
% of cpu time in user mode running niced processes
.It \&sy
% of cpu time in system mode
.It \&in
% of cpu time in interrupt mode
.It \&id
% of cpu time in idle mode
.El
.El
.Sh FILES
.Bl -tag -width /boot/kernel/kernel -compact
.It Pa /boot/kernel/kernel
Default kernel namelist.
.It Pa /dev/kmem
Default memory file.
.El
.Sh EXAMPLES
.Dl iostat -w 1 da0 da1 cd0
.Pp
Display statistics for the first two Direct Access devices and the first
CDROM device every second ad infinitum.
.Pp
.Dl iostat -c 2
.Pp
Display the statistics for the first four devices in the system twice, with
a one second display interval.
.Pp
.Dl iostat -t da -t cd -w 1
.Pp
Display statistics for all CDROM and Direct Access devices every second
ad infinitum.
.Pp
.Dl iostat -t da,scsi,pass -t cd,scsi,pass
.Pp
Display statistics once for all SCSI passthrough devices that provide access
to either Direct Access or CDROM devices.
.Pp
.Dl iostat -h -n 8 -w 1
.Pp
Display up to 8 devices with the most I/O every second ad infinitum.
.Pp
.Dl iostat -dh -t da -w 1
.Pp
Omit the TTY and CPU displays, show devices in order of performance and
show only Direct Access devices every second ad infinitum.
.Pp
.Dl iostat -Iw 3
.Pp
Display total statistics every three seconds ad infinitum.
.Pp
.Dl iostat -odICTw 2 -c 9
.Pp
Display total statistics using the old-style output format 9 times, with
a two second interval between each measurement/display.
The
.Fl d
flag generally disables the TTY and CPU displays, but since the
.Fl T
and
.Fl C
flags are given, the TTY and CPU displays will be displayed.
.Sh SEE ALSO
.Xr fstat 1 ,
.Xr netstat 1 ,
.Xr nfsstat 1 ,
.Xr ps 1 ,
.Xr systat 1 ,
.Xr devstat 3 ,
.Xr ctlstat 8 ,
.Xr gstat 8 ,
.Xr pstat 8 ,
.Xr vmstat 8
.Pp
The sections starting with ``Interpreting system activity'' in
.%T "Installing and Operating 4.3BSD" .
.Sh HISTORY
This version of
.Nm
first appeared in
.Fx 3.0 .
.Sh AUTHORS
.An Kenneth Merry Aq Mt ken@FreeBSD.org
.Sh BUGS
The use of
.Nm
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.