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

NAME
     iostat -- report I/O statistics

SYNOPSIS
     iostat [-CUdKIoT?] [-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:

     -?    Display a usage statement and exit.

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

     -c    Repeat the display count times.  If no wait interval is specified,
           the default is 1 second.

     -d    Display only device statistics.  If this flag is turned on, only
           device statistics will be displayed, unless -C or -U or -T is also
           specfied to enable the display of CPU, load average or TTY statis-
           tics.

     -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.

     -U    Display system load averages.  This is on by default, unless -d is
           specified.

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

     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