iostat(1)



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

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

SYNOPSIS
       iostat [ -c ] [ -d ] [ -h ] [ -k | -m ] [ -N ] [ -s ] [ -t ] [ -V  ]  [
       -x  ] [ -y ] [ -z ] [ -j { ID | LABEL | PATH | UUID | ... } ] [ -o JSON
       ] [ [ -H ] -g group_name ] [ --human ] [ -p [ device [,...] | ALL ] ] [
       device [...] | ALL ] [ 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, unless the  -y  option
       is  used (in this case, this first report is omitted).  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 displayed 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 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 Uti-
              lization Report. For multiprocessor systems, the CPU values  are
              global  averages  among all processors.  The report has the fol-
              lowing 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.

              %system
                     Show the percentage  of  CPU  utilization  that  occurred
                     while executing at the system level (kernel).

              %iowait
                     Show  the  percentage  of  time that the CPU or CPUs were
                     idle during which the system had an outstanding disk  I/O
                     request.

              %steal
                     Show  the percentage of time spent in involuntary wait by
                     the virtual CPU or CPUs while the hypervisor was  servic-
                     ing another virtual processor.

              %idle
                     Show  the  percentage  of  time that the CPU or CPUs were
                     idle and the system did not have an outstanding disk  I/O
                     request.

       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. Block devices and parti-
              tions for which statistics are to be displayed may be entered on
              the  command  line.  If no device nor partition is entered, then
              statistics are displayed for every device used  by  the  system,
              and  providing  that the kernel maintains statistics for it.  If
              the ALL keyword is given on the command  line,  then  statistics
              are  displayed for every device defined by the system, including
              those that have never been used.  Transfer rates are shown in 1K
              blocks  by default, unless the environment variable POSIXLY_COR-
              RECT is set, in which case 512-byte blocks are used.  The report
              may show the following fields, depending on the flags used:

              Device:
                     This  column  gives  the  device  (or  partition) name as
                     listed in the /dev directory.

              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 inde-
                     terminate size.

              Blk_read/s (kB_read/s, MB_read/s)
                     Indicate  the  amount  of  data  read  from  the   device
                     expressed  in  a  number of blocks (kilobytes, megabytes)
                     per second. Blocks are equivalent to sectors  and  there-
                     fore have a size of 512 bytes.

              Blk_wrtn/s (kB_wrtn/s, MB_wrtn/s)
                     Indicate  the  amount  of  data  written  to  the  device
                     expressed in a number of  blocks  (kilobytes,  megabytes)
                     per second.

              Blk_read (kB_read, MB_read)
                     The total number of blocks (kilobytes, megabytes) read.

              Blk_wrtn (kB_wrtn, MB_wrtn)
                     The  total  number of blocks (kilobytes, megabytes) writ-
                     ten.

              r/s
                     The number (after merges) of read requests completed  per
                     second for the device.

              w/s
                     The number (after merges) of write requests completed per
                     second for the device.

              sec/s (kB/s, MB/s)
                     The number of sectors (kilobytes, megabytes) read from or
                     written to the device per second.

              rsec/s (rkB/s, rMB/s)
                     The  number  of  sectors (kilobytes, megabytes) read from
                     the device per second.

              wsec/s (wkB/s, wMB/s)
                     The number of sectors (kilobytes, megabytes)  written  to
                     the device per second.

              rqm/s
                     The  number  of  I/O requests merged per second that were
                     queued to the device.

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

              wrqm/s
                     The  number of write requests merged per second that were
                     queued to the device.

              %rrqm
                     The percentage of read requests  merged  together  before
                     being sent to the device.

              %wrqm
                     The  percentage  of write requests merged together before
                     being sent to the device.

              areq-sz
                     The average size (in kilobytes) of the I/O requests  that
                     were issued to the device.
                     Note:  In  previous  versions,  this  field  was known as
                     avgrq-sz and was expressed in sectors.

              rareq-sz
                     The average size (in kilobytes) of the read requests that
                     were issued to the device.

              wareq-sz
                     The  average  size  (in  kilobytes) of the write requests
                     that were issued to the device.

              await
                     The average  time  (in  milliseconds)  for  I/O  requests
                     issued to the device to be served. This includes the time
                     spent by the requests in queue and the time spent servic-
                     ing them.

              r_await
                     The  average  time  (in  milliseconds)  for read requests
                     issued to the device to be served. This includes the time
                     spent by the requests in queue and the time spent servic-
                     ing them.

              w_await
                     The average time (in  milliseconds)  for  write  requests
                     issued to the device to be served. This includes the time
                     spent by the requests in queue and the time spent servic-
                     ing them.

              aqu-sz
                     The average queue length of the requests that were issued
                     to the device.
                     Note: In previous  versions,  this  field  was  known  as
                     avgqu-sz.

              svctm
                     The  average  service  time  (in  milliseconds)  for  I/O
                     requests that were issued to the device. Warning! Do  not
                     trust this field any more.  This field will be removed in
                     a future sysstat version.

              %util
                     Percentage of elapsed time during which I/O requests were
                     issued  to  the  device  (bandwidth  utilization  for the
                     device). Device saturation  occurs  when  this  value  is
                     close to 100% for devices serving requests serially.  But
                     for devices serving requests in parallel,  such  as  RAID
                     arrays  and  modern  SSDs,  this  number does not reflect
                     their performance limits.

OPTIONS
       -c     Display the CPU utilization report.

       -d     Display the device utilization report.

       -g group_name { device [...] | ALL }
              Display statistics for a group of devices.  The  iostat  command
              reports statistics for each individual device in the list then a
              line of global statistics for the group displayed as  group_name
              and  made  up  of  all  the devices in the list. The ALL keyword
              means that all the block devices defined by the system shall  be
              included in the group.

       -H     This  option must be used with option -g and indicates that only
              global statistics for the group are to  be  displayed,  and  not
              statistics for individual devices in the group.

       -h     Make  the  Device  Utilization Report easier to read by a human.
              --human is enabled implicitly with this option.

       --human
              Print sizes in human readable format (e.g. 1k, 1.23M, etc.)  The
              units  displayed  with  this  option supersede any other default
              units (e.g.  kilobytes, sectors...) associated with the metrics.

       -j { ID | LABEL | PATH | UUID | ... } [ device [...] | ALL ]
              Display persistent device names. Options ID, LABEL, etc. specify
              the  type of the persistent name. These options are not limited,
              only prerequisite is that  directory  with  required  persistent
              names is present in /dev/disk.  Optionally, multiple devices can
              be specified in the chosen persistent name type.   Because  per-
              sistent device names are usually long, option

       -k     Display statistics in kilobytes per second.

       -m     Display statistics in megabytes per second.

       -N     Display the registered device mapper names for any device mapper
              devices.  Useful for viewing LVM2 statistics.

       -o JSON
              Display the statistics in JSON (Javascript Object Notation) for-
              mat.   JSON  output field order is undefined, and new fields may
              be added in the future.

       -p [ { device [,...] | ALL } ]
              The -p option displays statistics  for  block  devices  and  all
              their  partitions that are used by the system.  If a device name
              is entered on the command line, then statistics for it  and  all
              its  partitions  are  displayed. Last, the ALL keyword indicates
              that statistics have to be displayed for all the  block  devices
              and  partitions defined by the system, including those that have
              never been used. If option -j is  defined  before  this  option,
              devices  entered  on  the command line can be specified with the
              chosen persistent name type.

       -s     Display a short (narrow) version of the report that  should  fit
              in 80 characters wide screens.

       -t     Print  the  time for each report displayed. The timestamp format
              may depend on the value of the S_TIME_FORMAT  environment  vari-
              able (see below).

       -V     Print version number then exit.

       -x     Display extended statistics.

       -y     Omit first report with statistics since system boot, if display-
              ing multiple records at given interval.

       -z     Tell iostat to omit output for any devices for which  there  was
              no activity during the sample period.

ENVIRONMENT
       The  iostat  command takes into account the following environment vari-
       ables:

       POSIXLY_CORRECT
              When this variable is set, transfer rates are shown in  512-byte
              blocks instead of the default 1K blocks.

       S_COLORS
              When  this  variable  is set, display statistics in color on the
              terminal.  Possible values for this variable are  never,  always
              or auto (the latter is the default).

              Please  note  that  the  color (being red, yellow, or some other
              color) used to display a value is not indicative of any kind  of
              issue  simply  because of the color. It only indicates different
              ranges of values.

       S_COLORS_SGR
              Specify the colors and other attributes used to display  statis-
              tics  on  the  terminal.  Its value is a colon-separated list of
              capabilities            that             defaults             to
              H=31;1:I=32;22:M=35;1:N=34;1:Z=34;22.    Supported  capabilities
              are:

              H=     SGR (Select Graphic Rendition) substring  for  percentage
                     values greater than or equal to 75%.

              I=     SGR substring for device names.

              M=     SGR substring for percentage values in the range from 50%
                     to 75%.

              N=     SGR substring for non-zero statistics values.

              Z=     SGR substring for zero values.

       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  8601  format
              (YYYY-MM-DD)  instead.   The  timestamp displayed with option -t
              will also be compliant with ISO 8601 format.

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.

       iostat -x sda sdb 2 6
              Display  six reports of extended statistics at two second inter-
              vals for devices sda and sdb.

       iostat -p sda 2 6
              Display six reports at two second intervals for device  sda  and
              all its partitions (sda1, etc.)

BUGS
       /proc filesystem must be mounted for iostat to work.

       Kernels older than 2.6.x are no longer supported.

       The  average  service  time  (svctm field) value is meaningless, as I/O
       statistics are now calculated at block level, and we  don't  know  when
       the  disk  driver  starts  to  process a request. For this reason, this
       field will be removed in a future sysstat version.

FILES
       /proc/stat contains system statistics.

       /proc/uptime contains system uptime.

       /proc/diskstats contains disks statistics.

       /sys contains statistics for block devices.

       /proc/self/mountstats contains statistics for network filesystems.

       /dev/disk contains persistent device names.

AUTHOR
       Sebastien Godard (sysstat <at> orange.fr)

SEE ALSO
       sar(1), pidstat(1), mpstat(1),  vmstat(8),  tapestat(1),  nfsiostat(1),
       cifsiostat(1)

       http://pagesperso-orange.fr/sebastien.godard/

Linux                              JUNE 2017                         IOSTAT(1)

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