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 ] [ --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  in-
       put/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 is-
                     sued  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  ex-
                     pressed  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 ex-
                     pressed 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 ex-
                     pressed 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.

              Blk_dscd (kB_dscd, MB_dscd)
                     The total number of blocks  (kilobytes,  megabytes)  dis-
                     carded.

              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 exe-
                     cuted by disks. Flush requests are not tracked for parti-
                     tions.  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  av-
                     grq-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  is-
                     sued  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 is-
                     sued 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 is-
                     sued  to  the device to be served. This includes the time
                     spent by the requests in queue and the time spent servic-
                     ing 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 servic-
                     ing them.

              f_await
                     The average time (in milliseconds) for flush requests is-
                     sued  to  the  device to be served.  The block layer com-
                     bines 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  de-
                     vice).  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  per-
                     formance 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  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, de-
              vices entered on the command line can be specified with the cho-
              sen 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).

              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 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 De-
              vices.

       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.

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/

Linux                            DECEMBER 2019                       IOSTAT(1)

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