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RedHat 9 (Linux i386) - man page for iostat (redhat section 1)

IOSTAT(1)			       Linux User's Manual				IOSTAT(1)

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

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  bal-
       ance 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 con-
       sists 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 displayed followed by a line of statistics for each device that  is  config-
       ured.

       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 parameter. If the  count
       parameter  is  specified, the value of count determines the number of reports generated at
       interval seconds apart. If the interval parameter is specified without the  count  parame-
       ter, 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  systems,	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
		     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 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 single I/O request to the device. A transfer is of  indeter-
		     minate 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 2.4 and later.

	      kB_read
		     The  total number of kilobytes read. Data displayed are valid only with ker-
		     nels 2.4 and later.

	      kB_wrtn
		     The total number of kilobytes written. Data displayed are	valid  only  with
		     kernels 2.4 and later.

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

	      wrqm/s
		     The number of write requests merged per  second  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
       -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  utiliza-
	      tion report.

       -k     Display statistics in kilobytes per second instead of blocks per second.	Data dis-
	      played are valid only with kernels 2.4 and later.

       -t     Print the time for each report displayed.

       -V     Print version number and usage then exit.

       -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/parti-
	      tions file. Please note that Linux kernel needs to be patched for  this  option  to
	      work.

ENVIRONMENT
       The iostat command takes into account the following environment 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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