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

NAME
     iostat -- report I/O statistics

SYNOPSIS
     iostat [-CdhKIoTxz?] [-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 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 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 repeat count is
           specified, the default is infinity.

     -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.

FreeBSD 6.2                     April 17, 2006                     FreeBSD 6.2

NAME | SYNOPSIS | DESCRIPTION | FILES | EXAMPLES | SEE ALSO | HISTORY | AUTHORS | BUGS

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