iostat(1) — Linux manual page

NAME | SYNOPSIS | DESCRIPTION | REPORTS | OPTIONS | ENVIRONMENT | EXAMPLES | BUGS | FILES | AUTHOR | SEE ALSO | COLOPHON

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

NAME         top

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

SYNOPSIS         top

       iostat [ -c ] [ -d ] [ -h ] [ -k | -m ] [ -N ] [ -s ] [ -t ] [ -V
       ] [ -x ] [ -y ] [ -z ] [ --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         top

       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         top

       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         top

       -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).

       -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.

       -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         top

       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         top

       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         top

       /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         top

       /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         top

       Sebastien Godard (sysstat <at> orange.fr)

SEE ALSO         top

       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/ 

COLOPHON         top

       This page is part of the sysstat (sysstat performance monitoring
       tools) project.  Information about the project can be found at 
       ⟨http://sebastien.godard.pagesperso-orange.fr/⟩.  If you have a
       bug report for this manual page, send it to sysstat-AT-orange.fr.
       This page was obtained from the project's upstream Git repository
       ⟨https://github.com/sysstat/sysstat.git⟩ on 2021-04-01.  (At that
       time, the date of the most recent commit that was found in the
       repository was 2021-02-15.)  If you discover any rendering
       problems in this HTML version of the page, or you believe there
       is a better or more up-to-date source for the page, or you have
       corrections or improvements to the information in this COLOPHON
       (which is not part of the original manual page), send a mail to
       man-pages@man7.org

Linux                         OCTOBER 2020                     IOSTAT(1)

Pages that refer to this page: cifsiostat(1)iostat2pcp(1)mpstat(1)nfsiostat-sysstat(1)pidstat(1)sar(1)tapestat(1)vmstat(8)