.\"	$OpenBSD: iostat.8,v 1.23 2007/05/31 19:20:25 jmc Exp $
.\"	$NetBSD: iostat.8,v 1.10 1996/10/25 18:21:57 scottr Exp $
.\"
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.\"	from: @(#)iostat.8	8.1 (Berkeley) 6/6/93
.\"
.Dd $Mdocdate: May 31 2007 $
.Dt IOSTAT 8
.Os
.Sh NAME
.Nm iostat
.Nd report I/O statistics
.Sh SYNOPSIS
.Nm iostat
.Op Fl CDdIT
.Op Fl c Ar count
.Op Fl M Ar core
.Op Fl N Ar system
.Op Fl w Ar wait
.Op Ar drives
.Sh DESCRIPTION
.Nm
displays kernel I/O statistics on terminal, disk and CPU operations.
By default,
.Nm
displays one line of statistics averaged over the machine's run time.
The use of
.Fl c
presents successive lines averaged over the
.Ar wait
period.
The
.Fl I
option causes
.Nm iostat
to print raw, unaveraged values.
.Pp
The options are as follows:
.Bl -tag -width Ds
.It Fl C
Show CPU statistics.
This is enabled by default unless the
.Fl D ,
.Fl d ,
or
.Fl T
flags are used.
.It Fl c Ar count
Repeat the display
.Ar count
times.
Unless the
.Fl I
flag is in effect, the first display is for the time since a reboot and
each subsequent report is for the time period since the last display.
If no
.Ar wait
interval is specified, the default is 1 second.
.It Fl D
Show alternate disk statistics.
Displays kilobytes transferred, number of
transfers, and time spent in transfers.
Use of this flag disables the default display.
.It Fl d
Show disk statistics.
This is the default.
Displays kilobytes per
transfer, number of transfers, and megabytes transferred.
Use of this flag disables display of CPU and tty statistics.
.It Fl I
Show the running total values, rather than an average.
.It Fl M Ar core
Extract values associated with the name list from the specified
.Ar core
instead of the default
.Pa /dev/mem .
.It Fl N Ar system
Extract the name list from the specified
.Ar system
instead of the default
.Dq Pa /bsd .
.It Fl T
Show tty statistics.
This is enabled by default unless the
.Fl C ,
.Fl D ,
or
.Fl d
flags are used.
.It Fl w Ar wait
Pause
.Ar wait
seconds between each display.
If no repeat
.Ar count
is specified, the default is infinity.
.El
.Pp
.Nm
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 disks
Disk operations.
The header of the field is the disk name and unit number.
If more than four disk drives are configured in the system,
.Nm
displays only the first four drives.
To force
.Nm
to display specific drives, their names may be supplied on the command
line.
.Pp
.Bl -tag -width indent -compact
.It KB/t
Kilobytes transferred per disk transfer
.It t/s
Transfers per second
.It MB/s
Megabytes transferred per second
.Pp
.El
The alternate display format, (selected with
.Fl D ) ,
presents the following values:
.Pp
.Bl -tag -width indent -compact
.It KB
Kilobytes transferred
.It xfr
Disk transfers
.It time
Seconds spent in disk activity
.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 processing interrupts
.It \&id
% of CPU time in idle mode
.El
.El
.Sh FILES
.Bl -tag -width /dev/mem -compact
.It Pa /bsd
default kernel namelist
.It Pa /dev/mem
default memory file
.El
.Sh SEE ALSO
.Xr fstat 1 ,
.Xr netstat 1 ,
.Xr nfsstat 1 ,
.Xr ps 1 ,
.Xr systat 1 ,
.Xr top 1 ,
.Xr pstat 8 ,
.Xr vmstat 8
.Pp
The sections starting with
.Dq Interpreting system activity
in
.%T "Installing and Operating 4.3BSD" .