iostat - report I/O statistics
iostat [ option ] ... [ interval [ count ] ]
Iostat delves into the system and reports certain statistics kept about input-output
activity. Information is kept about up to three different disks (RF, RK, RP) and about
typewriters. For each disk, IO completions and number of words transferred are counted;
for typewriters collectively, the number of input and output characters are counted.
Also, each sixtieth of a second, the state of each disk is examined and a tally is made if
the disk is active. The tally goes into one of four categories, depending on whether the
system is executing in user mode, in `nice' (background) user mode, in system mode, or
idle. From all these numbers and from the known transfer rates of the devices it is pos-
sible to determine information such as the degree of IO overlap and average seek times for
The optional interval argument causes iostat to report once each interval seconds. The
first report is for all time since a reboot and each subsequent report is for the last
The optional count argument restricts the number of reports.
With no option argument iostat reports for each disk the number of transfers per minute,
the milliseconds per average seek, and the milliseconds per data transfer exclusive of
seek time. It also gives the percentage of time the system has spend in each of the four
categories mentioned above.
The following options are available:
-t Report the number of characters of terminal IO per second as well.
-i Report the percentage of time spend in each of the four categories mentioned above,
the percentage of time each disk was active (seeking or transferring), the percent-
age of time any disk was active, and the percentage of time spent in `IO wait:'
idle, but with a disk active.
-s Report the raw timing information: 32 numbers indicating the percentage of time
spent in each of the possible configurations of 4 system states and 8 IO states (3
disks each active or not).
-b Report on the usage of IO buffers.