iostat - report I/O statistics
iostat [ drives ] [ interval [ count ] ]
Iostat iteratively reports the number of characters read and written to terminals per sec-
ond, and, for each disk, the number of transfers per second, kilobytes transferred per
second, and the milliseconds per average seek. It also gives the percentage of time the
system has spent in user mode, in user mode running low priority (niced) processes, in
system mode, and idling.
To compute this information, for each disk, seeks and data transfer completions and number
of words transferred are counted; for terminals collectively, the number of input and out-
put 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. From these numbers and given the
transfer rates of the devices it is possible to determine average seek times for each
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.
If more than 4 disk drives are configured in the system, iostat displays only the first 4
drives, with priority given to Massbus disk drives (i.e. if both Unibus and Massbus drives
are present and the total number of drives exceeds 4, then some number of Unibus drives
will not be displayed in favor of the Massbus drives). To force iostat to display spe-
cific drives, their names may be supplied on the command line.
4th Berkeley Distribution April 29, 1985 IOSTAT(1)