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iostat




SYNOPSIS

       iostat [ -c | -d ] [ -k ] [ -t ] [ -V ] [ -x [ device ]  ]
       [ interval [ count ] ]


DESCRIPTION

       The   iostat   command   is  used  for  monitoring  system
       input/output device loading  by  observing  the  time  the
       devices  are  active in relation to their average transfer
       rates. The iostat command generates reports  that  can  be
       used  to change system configuration to better balance the
       input/output load between physical disks.

       The first report generated by the iostat command  provides
       statistics  concerning  the  time  since  the  system  was
       booted. Each subsequent report covers the time  since  the
       previous report. All statistics are reported each time the
       iostat command is run. The report consists of a CPU header
       row followed by a row of CPU statistics. On multiprocessor
       systems, CPU  statistics  are  calculated  system-wide  as
       averages among all processors. A device header row is dis­
       played followed by a line of statistics  for  each  device
       that is configured.

       The  interval  parameter  specifies  the amount of time in
       seconds between each report.  The  first  report  contains
       statistics  for the time since system startup (boot). Each
       subsequent report contains statistics collected during the
       interval  since  the  previous report. The count parameter
       can be specified in conjunction with the interval  parame­
       ter.  If  the  count  parameter is specified, the value of
       count determines the number of reports generated at inter­
       val  seconds apart. If the interval parameter is specified
       without the count parameter, the iostat command  generates
       reports continuously.


REPORTS

       The iostat command generates two types of reports, the CPU
       Utilization report and the Device Utilization report.

       CPU Utilization Report
              The first report generated by the iostat command is
              the CPU Utilization Report. For multiprocessor sys­
              tems, the CPU values are global averages among  all
              processors.  The report has the following format:

              %user
                     Show  the percentage of CPU utilization that
                     occurred while executing at the  user  level
                     (application).
              %nice
              provides statistics on a  per  physical  device  or
              partition basis.  The report may show the following
              fields, depending on whether -x and -k options  are
              used or not:

              Device:
                     This  column gives the device name, which is
                     displayed as hdiskn with 2.2  kernels,   for
                     the  nth  device.  It is displayed as devm-n
                     with newer kernels, where  m  is  the  major
                     number  of  the  device, and n a distinctive
                     number.  When -x option is used, the  device
                     name as listed in the /dev directory is dis­
                     played.

              tps
                     Indicate the number of transfers per  second
                     that  were  issued to the device. A transfer
                     is an I/O request to  the  device.  Multiple
                     logical requests can be combined into a sin­
                     gle I/O request to the device. A transfer is
                     of indeterminate size.

              Blk_read/s
                     Indicate  the  amount  of data read from the
                     drive expressed in a number  of  blocks  per
                     second.  Blocks  are  equivalent  to sectors
                     with post 2.4 kernels and therefore  have  a
                     size  of  512  bytes.  With older kernels, a
                     block is of indeterminate size.

              Blk_wrtn/s
                     Indicate the amount of data written  to  the
                     drive  expressed  in  a number of blocks per
                     second.

              Blk_read
                     The total number of blocks read.

              Blk_wrtn
                     The total number of blocks written.

              kB_read/s
                     Indicate the amount of data  read  from  the
                     drive  expressed  in  kilobytes  per second.
                     Data displayed are valid only  with  kernels
                     2.4 and later.

              kB_wrtn/s
                     Indicate  the  amount of data written to the
                     drive expressed  in  kilobytes  per  second.
                     Data  displayed  are valid only with kernels
                     ond that were issued to the device.

              wrqm/s
                     The number of write requests merged per sec­
                     ond that were issued to the device.

              r/s
                     The number of read requests that were issued
                     to the device per second.

              w/s
                     The  number  of  write  requests  that  were
                     issued to the device per second.

              rsec/s
                     The number of sectors read from  the  device
                     per second.

              wsec/s
                     The  number of sectors written to the device
                     per second.

              rkB/s
                     The number of kilobytes read from the device
                     per second.

              wkB/s
                     The  number  of  kilobytes  written  to  the
                     device per second.

              avgrq-sz
                     The  average  size  (in  sectors)   of   the
                     requests that were issued to the device.

              avgqu-sz
                     The  average  queue  length  of the requests
                     that were issued to the device.

              await
                     The average time (in milliseconds)  for  I/O
                     requests  issued to the device to be served.

              svctm
                     The average service time  (in  milliseconds)
                     for  I/O  requests  that  were issued to the
                     device.

              %util
                     Percentage of  CPU  time  during  which  I/O
                     requests were issued to the device.


OPTIONS

       -x device
              Display  extended statistics. If no device is given
              on the command line, then extended  statistics  are
              displayed   for  every  device  registered  in  the
              /proc/partitions file. Please note that Linux  ker­
              nel needs to be patched for this option to work.


ENVIRONMENT

       The  iostat command takes into account the following envi­
       ronment variable:

       S_TIME_FORMAT
              If this variable exists and its value is  ISO  then
              the  current  locale  will be ignored when printing
              the date in the report header.  The iostat  command
              will use the ISO format (YYYY-MM-DD) instead.


EXAMPLES

       iostat
              Display  a single history since boot report for all
              CPU and Devices.

       iostat -d 2
              Display a continuous device report  at  two  second
              intervals.

       iostat -d 2 6
              Display six reports at two second intervals for all
              devices.


BUGS

       /proc filesystem must be mounted for iostat to work.


FILE

       /proc/stat contains system statisitics.

       /proc/partitions contains statistics for the devices.


AUTHOR

       Sebastien Godard <sebastien.godard@wanadoo.fr>


SEE ALSO

       vmstat(8), sar(1), mpstat(1)

       http://perso.wanadoo.fr/sebastien.godard/

Linux                      JANUARY 2002                 IOSTAT(1)
  
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