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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
       the devices.

       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)