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

# NAME

`iostat` — report I/O statistics

# SYNOPSIS

`iostat` | [`-CDdIT`] [`-c` count] [`-M` core] [`-N` system] [`-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 `-I` option causes `iostat` to print raw, unaveraged values.

The options are as follows:

`-C`
  Show CPU statistics. This is enabled by default unless the `-D`, `-d`, or `-T` flags are used.
`-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. Unless overridden by the `-w` option, the wait interval between lines is 1 second.
`-D`
  Show alternate disk statistics. Displays kilobytes transferred, number of transfers, and time spent in transfers. Use of this flag disables the default display.
`-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.
`-I`
  Show the running total values, rather than an average.
`-M` core
  Extract values associated with the name list from the specified core instead of the default /dev/mem.
`-N` system
  Extract the name list from the specified system instead of the default “/bsd”.
`-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. Unless a count is specified via the `-c` option, `iostat` will display output until it is interrupted.

`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 than four disk drives are configured in the system, `iostat` displays only the first four drives. To force `iostat` to display specific drives, their names may be supplied on the command line.

  KB/t
    Kilobytes transferred per disk transfer
  t/s
    Transfers per second
  MB/s
    Megabytes transferred per second

  The alternate display format, selected with `-D`, presents the following values:

  KB
    Kilobytes transferred
  xfr
    Disk transfers
  time
    Seconds spent in disk activity
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
  sp
    % of CPU time spent spinning
  in
    % of CPU time processing interrupts
  id
    % of CPU time in idle mode

# FILES

/bsd
  default kernel namelist
/dev/mem
  default memory file

# SEE ALSO

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

The sections starting with “Interpreting system activity” in Installing and Operating 4.3BSD.

September 17, 2022 | Debian