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

iostat — report I/O statistics

iostat [-CdDITxy] [-c count] [-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 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:

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.
Show CPU statistics. This is enabled by default unless the -d, -D, -T, or -x flags are used.
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 alternative disk statistics. Displays kilobytes transferred, number of transfers, and time spent in transfers. Use of this flag disables the default display.
Show the running total values, rather than an average.
Show tty statistics. This is enabled by default unless the -C, -d, or -D flags are used.
wait
Pause wait seconds between each display. If no repeat count is specified, the default is infinity.
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.
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 () 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

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.

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-9.2