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

     iostat -- report I/O statistics

     iostat [-CdhKIoT?]	[-c count] [-M core] [-n devs] [-N system] [-t
	    type,if,pass] [-w wait] [drives]

     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 wait interval	is specified,
	   the default is 1 second.

     -C	   Display CPU statistics.  This is on by default, unless -d is	speci-

     -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 de-
	   fault "/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

		   IDE	      Integrated Drive Electronics devices
		   SCSI	      Small Computer System Interface devices
		   other      Any other	device interface

		   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-

     -w	   Pause wait seconds between each display.  If	no repeat count	is
	   specified, the default is infinity.

     -?	   Display a usage statement and exit.

     The iostat	utility	displays its information in the	following format:

	   tin	   characters read from	terminals
	   tout	   characters written to terminals

	   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 old-style iostat	display	(using -o) shows the following statis-

	   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

	   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

     /boot/kernel/kernel  Default kernel namelist.
     /dev/kmem		  Default memory file.

	   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 ac-
     cess 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.

     fstat(1), netstat(1), nfsstat(1), ps(1), systat(1), gstat(8), pstat(8),

     The sections starting with	``Interpreting system activity'' in Installing
     and Operating 4.3BSD.

     This version of iostat first appeared in FreeBSD 3.0.

     Kenneth Merry <>

     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			       December	22, 1997			   BSD


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