Provided by: sysstat_12.0.1-1_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 ] [
       --dec={  0  |  1 | 2 } ] [ -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
       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:

              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_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.

              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 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.

              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.

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

       -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. 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. 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 persistent
              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) format.  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 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
              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).

              Note: On Debian sysstems the  colors  are  displayed  by  default  when  output  is
              connected to the terminal, even if this variable is not set (i.e. unset variable is
              treated as if it were set to auto).

              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.

       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)

       https://github.com/sysstat/sysstat

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