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 in‐
       put/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 expresssed 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 2020-11-01.  (At that
       time, the date of the most recent commit that was found in the repos‐
       itory was 2020-10-31.)  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 im‐
       provements 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)