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IOSTAT(8)		  BSD System Manager's Manual		     IOSTAT(8)

NAME
     iostat — report I/O statistics

SYNOPSIS
     iostat [-CdhIKoTxz?] [-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 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.

     The options are as follows:

     -c	   Repeat the display count times.  If no repeat count is specified,
	   the default is infinity.

     -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 speci‐
	   fied 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 period.

     -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 present.

     -N	   Extract the name list from the specified system instead 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 transfers, and mil‐
	   liseconds 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 devices
		   SCSI	      Small Computer System Interface devices
		   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 device 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 displayed 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 wait interval is
	   specified, the default is 1 second.

     -x	   Show extended disk statistics.  Each disk is displayed on a line of
	   its own with all available statistics.

     -z	   If -x is specified, omit lines for devices with no activity.

     -?	   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 device name and
	   unit number.	 The iostat 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 -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 sup‐
	   plied on the command line.  The iostat utility will not display
	   more devices than will fit in an 80 column screen, unless 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 com‐
	   mand 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 extended iostat device display, with the -x flag specified,
	   shows the following statistics:

	   r/s	   read operations per second
	   w/s	   write operations per second
	   kr/s	   kilobytes read per second
	   kw/s	   kilobytes write per second
	   wait	   transactions queue length
	   svc_t   average duration of transactions, in milliseconds
	   %b	   % of time the device had one or more outstanding transac‐
		   tions

	   The old-style iostat display (using -o) shows the following statis‐
	   tics:

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

	   The old-style iostat display, with the -I flag specified, 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 processes
	   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 performance 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 gen‐
     erally 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), devstat(3), 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 only cover the
     time immediately before the crash.

BSD				April 17, 2006				   BSD
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