iostat

SYNOPSIS
       iostat [ -c ] [ -d ] [ -h ] [ -k | -m ] [ -N ] [ -t ] [ -V ] [ -x  ]  [
       -y  ]  [  -z  ]  [  -j { ID | LABEL | PATH | UUID | ... } ] [ [ -H ] -g
       group_name ] [ -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 parame-
       ter, 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 Uti-
              lization Report. For multiprocessor systems, the CPU values  are
              global  averages  among all processors.  The report has the fol-
              lowing 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

       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 parti-
              tions 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_COR-
              RECT 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 inde-
                     terminate 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  there-
                     fore 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) writ-
                     ten.

              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.

              r/s
                     The  number  of sectors (kilobytes, megabytes) written to
                     the device per second.

              avgrq-sz
                     The average size (in sectors) of the requests  that  were
                     issued to the device.

              avgqu-sz
                     The average queue length of the 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 servic-
                     ing 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 servic-
                     ing 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 servic-
                     ing them.

              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

       -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  is  enabled
              implicitly 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.

       -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.

       -t     Print the time for each report displayed. The  timestamp  format
              may  depend  on the value of the S_TIME_FORMAT environment vari-
              able (see below).

       -V     Print version number then exit.

       -x     Display extended statistics.

       -y     Omit first report with statistics since system boot, if display-
              ing 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  vari-
       ables:

       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
              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  inter-
              vals 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.


Linux                            OCTOBER 2015                        IOSTAT(1)
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