iostat - Report Central Processing Unit (CPU) statistics and
input/output statistics for devices and partitions.
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 ] ]
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.
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.
- -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.
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.
- 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.)
/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.
/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.
Sebastien Godard (sysstat <at> orange.fr)