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

NAME
     iostat – report I/O statistics

SYNOPSIS
     iostat [-CUdKIoT?] [-c count] [-n devs] [-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:

     -?    Display a usage statement and exit.

     -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
           specified.

     -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
           specified to enable the display of CPU, load average or TTY
           statistics.

     -I    Display total statistics for a given time period, rather than
           average 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.  The iostat utility will
           display fewer devices if there are not devs devices present.

     -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
           milliseconds per seek are displayed.

     -T    Display TTY statistics.  This is on by default, unless -d is
           specified.

     -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.

     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
           supplied 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, 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
           statistics:

           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
     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 -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
     generally 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
     netstat(1), nfsstat(1), ps(1), top(1), vm_stat(1)

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

HISTORY
     This version of iostat first appeared in FreeBSD 3.0.

macOS 15.2                       May 22, 2015                       macOS 15.2