IOSTAT(8) System Manager's Manual IOSTAT(8)
iostat - report I/O statistics
iostat [ -cdDIt ] [ -l n ] [ disk ... ] [ interval [ count ] ]
iostat can iteratively report terminal and disk I/O activity, as well
as CPU utilization. The first report is for all time since a reboot
and each subsequent report is for the prior interval only.
In order to compute this information, the kernel maintains a number of
counters. For each disk, seeks and data transfer completions and num-
ber of words transferred are counted; for terminals collectively, the
number of input and output characters are counted. Also, at each clock
tick, the state of each disk is examined and a tally is made if the
disk is active. The kernel also provides approximate transfer rates of
iostat's activity class options default to tdc (terminal, disk, and
CPU). If any activity class options are specified, the default is com-
pletely overridden. Therefore, if only -d is specified, neither termi-
nal nor CPU statistics will be reported. The last disk option speci-
fied (either -d or -D) is the only one that is used.
-c Report the percentage of time the system has spent in user mode,
in user mode running low priority processes, see nice(1), in
system mode, and idling.
-d For each disk, report the number of kilobytes transferred per
second, the number of transfers per second, and the milliseconds
per average seek (see BUGS below).
-D For each disk, report the reads per second, writes per second,
and percentage disk utilization.
-I Report the counts in each interval, rather than reporting rates.
-t Report the number of characters read and written to terminals.
-l n Limit the number of disks included in the report to n; the disk
limit defaults to 4. Note: disks explicitly requested (see disk
below) are not subject to this disk limit.
disk Explicitly specify the disks to be reported; in addition to any
explicit disks, any active disks up to the disk limit (see -l
above) will also be reported.
Report once each interval seconds.
count Only print count reports.
Milliseconds per average seek is an approximation based on the disk
(not the controller) transfer rate. Therefore, the seek time will be
over-estimated in systems with slower controllers.
iostat only provides statistics on the first ten disk drives, all oth-
ers are ignored.
7 October 1990 IOSTAT(8)