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

NAME
     iostat — report I/O statistics

SYNOPSIS
     iostat [-CdKIoT?] [-c count] [-n devs] [-w wait] [drives]

DESCRIPTION
     Iostat displays kernel I/O statistics on terminal, device and cpu opera‐
     tions.  The first statistics that are printed are averaged over the sys‐
     tem 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‐
	   fied.

     -d	   Display only device statistics.  If this flag is turned on, only
	   device statistics will be displayed, unless -C or -T is also spec‐
	   fied to enable the display of CPU or TTY statistics.

     -I	   Display total statstics 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.

     -n	   Display up to devs number of devices.  iostat will display fewer
	   devices if there aren't devs devices present.

     -o	   Display old-style iostat device statistics.	Sectors per second,
	   transfers per second, and miliseconds per seek are displayed.  If
	   -I is specified, total blocks/sectors, total transfers, and
	   miliseconds per seek are displayed.

     -T	   Display TTY statistics.  This is on by default, unless -d is speci‐
	   fied.

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

     -?	   Display a usage statement and exit.

     Iostat 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.	 iostat 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 supplied on
	   the command line.  iostat 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, 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, 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‐
	   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
	   sy	   % of cpu time in system mode
	   id	   % of cpu time in idle mode

EXAMPLES
	   iostat -w 1 disk0 disk2

     Display statistics for the first and third disk devices device every sec‐
     ond ad infinitum.

	   iostat -c 2

     Display the statistics for the first four devices in the system twice,
     with a one second display interval.

	   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), pstat(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.

BSD			      September 27, 2001			   BSD
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