Provided by: sysstat_12.6.1-1ubuntu1_amd64 bug

NAME

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

SYNOPSIS

       iostat [ -c ] [ -d ] [ -h ] [ -k | -m ] [ -N ] [ -s ] [ -t ] [ -V ] [ -x ] [ -y ] [ -z ] [
       --compact  ]  [ --dec={ 0 | 1 | 2 } ] [ { -f | +f } directory ] [ -j { ID | LABEL | PATH |
       UUID | ... } ] [ -o JSON ] [ [ -H ] -g group_name ] [ --human  ]  [  --pretty  ]  [  -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
       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 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.

              %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 servicing 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  partitions  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_CORRECT is set, in which case
              512-byte blocks are used.  The report may show the following fields,  depending  on
              the flags used (e.g.  -x, -s and -k or -m):

              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
                     indeterminate 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 therefore 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_dscd/s (kB_dscd/s, MB_dscd/s)
                     Indicate the amount of data discarded for the device expressed in  a  number
                     of blocks (kilobytes, megabytes) per second.

              Blk_w+d/s (kB_w+d/s, MB_w+d/s)
                     Indicate the amount of data written to or discarded for 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) written.

              Blk_dscd (kB_dscd, MB_dscd)
                     The total number of blocks (kilobytes, megabytes) discarded.

              Blk_w+d (kB_w+d, MB_w+d)
                     The total number of blocks (kilobytes, megabytes) written or discarded.

              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.

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

              f/s    The  number  (after  merges)  of flush requests completed per second for the
                     device.  This counts flush requests executed by disks.  Flush  requests  are
                     not  tracked  for  partitions.   Before  being  merged, flush operations are
                     counted as writes.

              sec/s (kB/s, MB/s)
                     The number of sectors  (kilobytes,  megabytes)  read  from,  written  to  or
                     discarded for 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.

              dsec/s (dkB/s, dMB/s)
                     The  number  of  sectors (kilobytes, megabytes) discarded for 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.

              drqm/s The number of discard 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.

              %drqm  The  percentage of discard 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.

              dareq-sz
                     The average size (in kilobytes) of the discard 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 servicing 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 servicing 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 servicing them.

              d_await
                     The average time (in milliseconds) for discard requests issued to the device
                     to be served. This includes the time spent by the requests in queue and  the
                     time spent servicing them.

              f_await
                     The  average  time (in milliseconds) for flush requests issued to the device
                     to be served.  The block layer combines flush requests and executes at  most
                     one  at  a  time.   Thus  flush  operations could be twice as long: Wait for
                     current flush request, then execute it, then wait for the next one.

              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.

              %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.

       --compact
              Don't break the Device Utilization Report into sub-reports so that all the  metrics
              get displayed on a single line.

       -d     Display the device utilization report.

       --dec={ 0 | 1 | 2 }
              Specify the number of decimal places to use (0 to 2, default value is 2).

       -f directory
       +f directory
              Specify  an  alternative directory for iostat to read devices statistics. Option -f
              tells iostat to use only the files located in the  alternative  directory,  whereas
              option  +f  tells it to use both the standard kernel files and the files located in
              the alternative directory to read device statistics.

              directory is a directory containing files with statistics for  devices  managed  in
              userspace.  It may contain:

              - a "diskstats" file whose format is compliant with that located in "/proc",
              -  statistics  for  individual devices contained in files whose format is compliant
              with that of files located in "/sys".

              In particular, the following files located in directory may be used by iostat:

              directory/block/device/stat
              directory/block/device/partition/stat

              partition files must have an entry in directory/dev/block/ directory, e.g.:

              directory/dev/block/major:minor --> ../../block/device/partition

       -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     This option is equivalent to specifying --human --pretty.

       --human
              Print sizes in human readable format (e.g. 1.0k, 1.2M, 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. Keywords ID, LABEL, etc. specify the type  of  the
              persistent  name.  These  keywords  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
              persistent device names are usually long, option --pretty is  implicitly  set  with
              this 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)  format.   JSON  output
              field order is undefined, and new fields may be added in the future.

       -p [ { device[,...] | ALL } ]
              Display  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.

       --pretty
              Make the Device Utilization Report easier to read by a human.  The device name will
              be printed on the right side. The report may also be  broken  into  sub-reports  if
              there are many metrics to display (use --compact option to prevent this).

       -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 variable (see below).

       -V     Print version number then exit.

       -x     Display extended statistics.

       -y     Omit first report with statistics since system boot, if displaying 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 variables:

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

       S_COLORS
              By default statistics are displayed in color when the  output  is  connected  to  a
              terminal.   Use  this  variable  to  change  the settings. Possible values for this
              variable are never, always or  auto  (the  latter  is  equivalent  to  the  default
              settings).
              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 statistics 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 intervals 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.

       Although  iostat  speaks  of kilobytes (kB), megabytes (MB)..., it actually uses kibibytes
       (kiB), mebibytes (MiB)...  A kibibyte is equal to 1024 bytes, and a mebibyte is  equal  to
       1024 kibibytes.

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)

       https://github.com/sysstat/sysstat
       http://pagesperso-orange.fr/sebastien.godard/