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

# NAME

`iostat` —
report I/O statistics

# SYNOPSIS

`iostat` | [`-CdDITxy`] [`-c` count] [`-w` wait] [drives]

# DESCRIPTION

`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:

`-c` count
  Repeat the display count times. Unless the `-I` flag 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 `-x` flags 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 `-D` flags are used.
`-w` wait
  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, `iostat` displays only those drives that fit on the display. To force `iostat` to display specific drives, they may be supplied on the command line, either as names or `fnmatch`() 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 `-y` flag, 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

# SEE ALSO

fstat(1), netstat(1), nfsstat(1), ps(1), systat(1), vmstat(1), fnmatch(3), pstat(8)

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

# HISTORY

`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.

July 29, 2018 | NetBSD 9.5