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\"      from: @(#)iostat.8      8.1 (Berkeley) 6/6/93
\"
Dd July 28, 2023
Dt IOSTAT 8
Os
Sh NAME
Nm iostat
Nd report I/O statistics
Sh SYNOPSIS
Nm
Op Fl CDdITXxyz
Op Fl c Ar count
Op Fl H Ar height
Op Fl W Ar width
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
or
Fl w
presents successive lines averaged over the
Ar wait
period.
The
Fl I
option causes
Nm
to print raw, unaveraged values (totals).
Pp
Only the last disk option specified
Fl ( d ,
Fl D ,
Fl X ,
Fl x ,
or
Fl y )
is used.
Pp
The options are as follows:
Bl -tag -width XNXsystemX
It Fl C
Show CPU statistics.
This is enabled by default unless any of the
Fl D ,
Fl d ,
Fl T ,
Fl X ,
Fl x ,
or
Fl y
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 alternative disk statistics.
Displays
number of transfers,
kilobytes transferred,
and
time spent in transfers,
during the
Ar wait
period (or since boot with
Fl I ) .
Use of this flag disables the default display.
It Fl d
Show disk statistics.
This is the default.
Displays
number of transfers per second,
kilobytes per transfer,
and
megabytes transferred per second.
Use of this flag disables the default display of CPU and tty statistics.
It Fl H Ar height
Set the page size (length, or height) explicitly, as the number of lines,
Ar height .
If not set, the page length is taken from the environment variable
Ev LINES
if set, or from the terminal (window) size, if output is to a terminal
and its size is set,
and otherwise defaults to 20.
If explicitly set to zero, pages are considered to be infinitely long.
This parameter determines the frequency at which repeated headers are output.
If the value is greater than zero, but too small for the header, along with
one output set, then a new header will be produced for each set of output.
It Fl I
Show the running total values, rather than an average.
ig ii
It Fl i
Like
Fl I
except the totals shown are those since
Nm
started running, rather than since the system booted.
In this case the first output would necessarily be zero,
so is suppressed.
Consequently this option produces no output if neither
Fl c
nor
Fl w
is given.
ii
It Fl T
Show tty statistics.
This is enabled by default unless one, or more, of the
Fl C ,
Fl D ,
Fl d ,
Fl X ,
Fl x ,
or
Fl y
flags are used.
ig uu
It Fl u
When totals are being shown
Pq Fl I
ig ii
Po or
Fl i Pc
ii
include a column after each relevant output column
showing the difference between this output and the previous.
These added columns will be blank in the first displayed output.
uu
It Fl W Ar width
Set the page width explicitly, as the number of columns of characters,
Ar width .
If not set, the page width is taken from the environment variable
Ev COLUMNS
if set, or from the terminal (window) size, if output is to a terminal
and its size is set,
and otherwise defaults to 80.
If explicitly set to 0, lines are considered infinitely long.
This width is used only to determine the number of drives to display
by default when no drive list is given.
In other cases output will be as wide as needed to display the
data requested.
It Fl w Ar wait
Pause
Ar wait
seconds between each display.
If no repeat
Ar count
is specified, the default is infinity.
It Fl X
Show limited alternative disk statistics.
Displays megabytes transferred, and time spent in transfers, during the
Ar wait
period (or since boot with
Fl I ) .
Use of this flag disables the default display.
It Fl x
Show extended disk statistics.
Each disk is displayed on a line of its own with all available
statistics.
This option overrides all other display options, and all
disks are displayed unless specific disk names
are provided as arguments.
Additionally, separate read and write statistics are displayed.
The
Fl C
and
Fl T
options are ignored with this output format.
It Fl y
Shows the extended statistics (as with
Fl x )
and additional queuing statistics.
Output does not fit in an 80 column window.
The
Fl C
and
Fl T
options are ignored with this output format.
It Fl z
Replaces drive and CPU statistic outputs that are exactly zero with spaces.
Note that zero values can still appear \(en this indicates a
value that was not zero, but was rounded down so appears as zero.
Drive output is replaced by spaces only when the drive did no
input or output at all in the interval,
or with
Fl I ,
has never done any I/O.
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 drives are configured in the system that fit across the
current display,
Nm
displays only those drives that fit on the display.
To force
Nm
to display specific drives, they may be supplied on the command
line, either as names or
Fn fnmatch
patterns.
Pp
Bl -tag -width indent -compact
It t/s
transfers per second
It KB/t
Kilobytes transferred per disk transfer
It MB/s
Megabytes transferred per second
El
Pp
The alternative display format, (selected with
Fl D ) ,
presents the following values:
Pp
Bl -tag -width indent -compact
It xfr
Disk transfers
It KB
Kilobytes transferred
It time
Seconds spent in disk activity
El
Pp
With the
Fl y
flag, the following queuing measurements are added:
Pp
Bl -tag -width indent -compact
It wait
Number of I/O requests queued up
It actv
Number of currently active I/O requests
It wsvc_t
Average waiting time of an I/O request in milliseconds
It asvc_t
Average duration of an I/O request in milliseconds
It wtime
Seconds spent in the waiting queue.
Queuing data might not be available from all drivers
and is then shown as zeros.
El
Pp
With the
Fl X
flag, the following queuing measurements are added:
Pp
Bl -tag -width indent -compact
It MB/s
Megabytes transferred per second
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 in interrupt mode
It \&id
% of CPU time in idle mode
El
Pp
Note that because of rounding, these percentages may
appear to total more or less than 100.
El
Sh SEE ALSO
Xr fstat 1 ,
Xr netstat 1 ,
Xr nfsstat 1 ,
Xr ps 1 ,
Xr systat 1 ,
Xr vmstat 1 ,
Xr fnmatch 3 ,
Xr pstat 8
Pp
The sections starting with ``Interpreting system activity'' in
%T "Installing and Operating 4.3BSD" .
Sh HISTORY
Nm
appeared in
At v6 .
The
Fl x
option was added in
Nx 1.4 .
Collection of queuing values and the
Fl y
option were added in
Nx 8.0 .
The
Fl X
option was added in
Nx 11.0 .
The archaic option format:
br
ti +3n
Nm
Op Ar drives ...
Oo Ar wait Oo Ar count Oc Oc
br
remains supported (the first
Ar drive
whose name starts with a digit is taken to be the
Ar wait
period) but is deprecated,
and may be removed in a future version,
so should not be used.

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