iostat  -  Report Central Processing Unit (CPU) statistics
       and input/output statistics for devices and partitions.


SYNOPSIS

       iostat [ -c | -d ] [ -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).

                     Show  the percentage of CPU utilization that
                     occurred while executing at the  user  level
                     with nice priority.
              %sys
                     Show  the percentage of CPU utilization that
                     occurred while executing at the system level
                     (kernel).
              %idle
                     Show  the percentage of time that the CPU or
                     CPUs were idle.

       Device Utilization Report
              The second report generated by the  iostat  command
              is the Device Utilization Report. The device report
              provides statistics on a  per  physical  device  or
              partition basis.  The report may show the following
              fields, depending on whether -x option is  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. 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. A block is of indeterminate size.

              Blk_read
                     The total number of blocks read.

              Blk_wrtn
                     The total number of blocks written.

                     The  number of read requests merged per sec­
                     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.

              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

       -c     The -c option is exclusive of  the  -d  option  and
              displays only the cpu usage report.

       -d     The  -d  option  is  exclusive of the -c option and
              displays only the device utilization report.

       -t     Print the time for each report displayed.


       -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

       Statistics in KB/s for each block device are not available
       by default due to Linux poor  disk  accounting.   For  the
       same  reason,  a  kernel  patch  needs  to  be applied for
       extended statistics to be displayed.

       /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)



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