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

iostatreport I/O statistics

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

The options are as follows:

Show CPU statistics. This is enabled by default unless the -D, -d, or -T flags are used.
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.
Show alternate disk statistics. Displays kilobytes transferred, number of transfers, and time spent in transfers. Use of this flag disables the default display.
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.
Show the running total values, rather than an average.
Extract values associated with the name list from the specified core instead of the default /dev/mem.
Extract the name list from the specified system instead of the default “/bsd”.
Show tty statistics. This is enabled by default unless the -C, -D, or -d flags are used.
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:

characters read from terminals
characters written to terminals
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.

Kilobytes transferred per disk transfer
Transfers per second
Megabytes transferred per second
The alternate display format, (selected with -D), presents the following values:

Kilobytes transferred
Disk transfers
Seconds spent in disk activity
% of CPU time in user mode
% of CPU time in user mode running niced processes
% of CPU time in system mode
% of CPU time processing interrupts
% of CPU time in idle mode

default kernel namelist
default memory file

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.

January 17, 2013 OpenBSD-5.9