- NetBSD Manual Pages
IOSTAT(8) NetBSD System Manager's Manual IOSTAT(8)
Powered by man-cgi (2021-03-02).
Maintained for NetBSD
by Kimmo Suominen.
Based on man-cgi by Panagiotis Christias.
iostat -- report I/O statistics
iostat [-CdDITxy] [-c count] [-w wait] [drives]
iostat displays kernel I/O statistics on terminal, disk and CPU opera-
tions. 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, unaver-
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
-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 kilo-
bytes per transfer, number of transfers, and megabytes trans-
ferred. Use of this flag disables display of CPU and tty
-D Show alternative disk statistics. Displays kilobytes trans-
ferred, 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 dis-
played unless specific disks are provided as arguments.
Additionally, separate read and write statistics are dis-
-y Shows the extended statistics and additional queuing statis-
iostat displays its information in the following format:
tin characters read from terminals
tout characters written to terminals
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
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
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.
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),
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.
NetBSD 9.1 July 29, 2018 NetBSD 9.1