bionic (1) iostat.1.gz

Provided by: sysstat_11.6.1-1ubuntu0.2_amd64 bug

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 ]  [  -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  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

       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:

              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 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.

       -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. 1k, 1.23M, 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 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 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
              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).

              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

       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 sysstat 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 <at> orange.fr)

SEE ALSO

       sar(1), pidstat(1), mpstat(1), vmstat(8), tapestat(1), nfsiostat(1), cifsiostat(1)

       http://pagesperso-orange.fr/sebastien.godard/