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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 } ] [ { -f | +f } directory ] [ -j { ID | LABEL | PATH | UUID | ... } ]
       [ -o JSON ] [ [ -H ] -g group_name ] [ --human ] [ --pretty ] [ -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 bal-
       ance 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  sta-
       tistics  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 dis-
       played 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  De-
       vice 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 en-
              tered 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,  un-
              less 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 di-
                     rectory.

              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  indeter-
                     minate 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  de-
                     vice.

              w/s    The number (after merges) of write requests completed per second for the de-
                     vice.

              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 de-
                     vice.  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  dis-
                     carded for the device per second.

              rsec/s (rkB/s, rMB/s)
                     The  number  of sectors (kilobytes, megabytes) read from the device per sec-
                     ond.

              wsec/s (wkB/s, wMB/s)
                     The number of sectors (kilobytes, megabytes) written to the device per  sec-
                     ond.

              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  de-
                     vice.

              wrqm/s The  number  of write requests merged per second that were queued to the de-
                     vice.

              drqm/s The number of discard requests merged per second that were queued to the de-
                     vice.

              %rrqm  The percentage of read requests merged together before being sent to the de-
                     vice.

              %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 ex-
                     pressed 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 cur-
                     rent 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  de-
                     vice  (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).

       -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  direc-
              tory  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 statis-
              tics 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
       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 ter-
              minal.  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 ig-
              nored 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.

       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
       /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                                      OCTOBER 2020                                 IOSTAT(1)

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