.\"
.\" 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.
.\"
.\" $FreeBSD$
.\"
.\" 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 May 22, 2015
.Dt IOSTAT 8
.Os
.Sh NAME
.Nm iostat
.Nd report
.Tn I/O
statistics
.Sh SYNOPSIS
.Nm
.Op Fl CUdKIoT?\&
.Op Fl c Ar count
.Op Fl n Ar devs
.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 ?\&
Display a usage statement and exit.
.It Fl c
Repeat the display
.Ar count
times.
If no
.Ar wait
interval is specified, the default is 1 second.
.It Fl C
Display CPU statistics.
This is on by default, unless
.Fl d
is specified.
.It Fl d
Display only device statistics.
If this flag is turned on, only device statistics will be displayed, unless
.Fl C
or
.Fl U
or
.Fl T
is also specified to enable the display of CPU, load average or TTY statistics.
.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 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
is specified.
.It Fl U
Display system load averages.
This is on by default, unless
.Fl d
is specified.
.It Fl w
Pause
.Ar wait
seconds between each display.
If no repeat
.Ar count
is specified, the default is infinity.
.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, 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,
.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 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 \&sy
% of cpu time in system mode
.It \&id
% of cpu time in idle mode
.El
.El
.Sh EXAMPLES
.Dl iostat -w 1 disk0 disk2
.Pp
Display statistics for the first and third disk devices 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 -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 netstat 1 ,
.Xr nfsstat 1 ,
.Xr ps 1 ,
.Xr top 1 ,
.Xr vm_stat 1
.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 .