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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 ] [ -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 ] ] [  de

       vice [...] | 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  con

       figuration 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, un

       less 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 config

       ured.

       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 dis

              played 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, in

              cluding 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 seri

                     ally.  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 dis

              played, 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.   Op

              tionally,  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 envi

              ronment 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-sepa

              rated 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 sys

       stat 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  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                                                       JULY 2018                                                  IOSTAT(1)

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