iostat —
report I/O statistics
  
    | iostat | [ -CdDITxy] [-ccount] [-wwait] [drives] | 
iostat displays kernel I/O statistics on terminal, disk
  and CPU operations. By default, iostat displays one
  line of statistics averaged over the machine's run time. The use of
  -c presents successive lines averaged over the
  wait period. The -I option
  causes iostat to print raw, unaveraged values.
Only the last disk option specified (-d,
    -D, or -x) is used.
The options are as follows:
  - -ccount
- Repeat the display count times. Unless the
      -Iflag is in effect, the first display is for the
      time since a reboot and each subsequent report is for the time period
      since the last display. If no wait interval is
      specified, the default is 1 second.
- -C
- Show CPU statistics. This is enabled by default unless the
      -d,-D,-T, or-xflags are
    used.
- -d
- Show disk statistics. This is the default. Displays kilobytes per
      transfer, number of transfers, and megabytes transferred. Use of this flag
      disables display of CPU and tty statistics.
- -D
- Show alternative disk statistics. Displays kilobytes transferred, number
      of transfers, and time spent in transfers. Use of this flag disables the
      default display.
- -I
- Show the running total values, rather than an average.
- -T
- Show tty statistics. This is enabled by default unless the
      -C,-d, or-Dflags are used.
- -wwait
- 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. This option overrides all other display
      options, and all disks are displayed unless specific disks are provided as
      arguments. Additionally, separate read and write statistics are
    displayed.
- -y
- Shows the extended statistics and additional queuing statistics.
iostat displays its information in the
    following format:
  - tty
- 
    
      - tin
- characters read from terminals
- tout
- characters written to terminals
 
- disks
- Disk operations. The header of the field is the disk name and unit number.
      If more drives are configured in the system that fit across the current
      display, iostatdisplays only those drives that
      fit on the display. To forceiostatto display
      specific drives, they may be supplied on the command line, either as names
      orfnmatch() patterns.
      - KB/t
- Kilobytes transferred per disk transfer
- t/s
- transfers per second
- MB/s
- Megabytes transferred per second
 The alternative display format, (selected with-D),
      presents the following values.
      - KB
- Kilobytes transferred
- xfr
- Disk transfers
- time
- Seconds spent in disk activity
 With the-yflag, the following queuing measurements
      are added
      - wait
- Number of I/O requests queued up
- actv
- Number of currently active I/O requests
- wsvc_t
- Average waiting time of an I/O request in milliseconds
- asvc_t
- Average duration of an I/O request in milliseconds
- wtime
- Seconds spent in the waiting queue. Queuing data might not be
          available from all drivers and is then shown as zeros.
 
- 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
 
iostat appeared in Version 6
  AT&T UNIX. The -x option was added in
  NetBSD 1.4. Collection of queueing values and the
  -y option were added in NetBSD
  8.0.