IOSTAT(1) Linux User's Manual IOSTAT(1)
NAME
iostat - Report Central Processing Unit (CPU) statistics and input/out-
put statistics for devices and partitions.
SYNOPSIS
iostat [ -c ] [ -d ] [ -h ] [ -k | -m ] [ -N ] [ -s ] [ -t ] [ -V ] [ -x
] [ -y ] [ -z ] [ --compact ] [ --dec={ 0 | 1 | 2 } ] [ { -f | +f } di-
rectory ] [ -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 balance the in-
put/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 re-
port covers the time since the previous report. All statistics are re-
ported each time the iostat command is run. The report consists of a CPU
header row followed by a row of CPU statistics. On multiprocessor sys-
tems, CPU statistics are calculated system-wide as averages among all
processors. A device header row is displayed followed by a line of sta-
tistics 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 follow-
ing 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 re-
quest.
%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 re-
quest.
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_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 is-
sued 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 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 ex-
pressed 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 ex-
pressed 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) dis-
carded.
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 exe-
cuted by disks. Flush requests are not tracked for parti-
tions. 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 be-
ing 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 av-
grq-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 is-
sued 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 is-
sued to the device to be served. This includes the time
spent by the requests in queue and the time spent servic-
ing 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 servic-
ing them.
f_await
The average time (in milliseconds) for flush requests is-
sued 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 de-
vice). 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 per-
formance limits.
OPTIONS
-c Display the CPU utilization report.
--compact
Don't break the Device Utilization Report into sub-reports so
that all the metrics get displayed on a single line.
-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 sta-
tistics. 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 alterna-
tive directory to read device statistics.
directory is a directory containing files with statistics for de-
vices 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 for-
mat 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/ direc-
tory, 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 in-
cluded 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 sta-
tistics 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 persis-
tent 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) for-
mat. 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 op-
tion -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.
The device name will be printed on the right side. The report may
also be broken into sub-reports if there are many metrics to dis-
play (use --compact option to prevent this).
-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 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
By default statistics are displayed in color when the output is
connected to a terminal. Use this variable to change the set-
tings. 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 statis-
tics on the terminal. Its value is a colon-separated list of ca-
pabilities that defaults to I=32;22:N=34;1:W=35;1:X=31;1:Z=34;22.
Supported capabilities are:
I= SGR (Select Graphic Rendition) substring for device names.
N= SGR substring for non-zero statistics values.
W= (or M=)
SGR substring for percentage values in the range from 75%
to 90% (or in the range 10% to 25% depending on the met-
ric's meaning).
X= (or H=)
SGR substring for percentage values greater than or equal
to 90% (or lower than or equal to 10% depending on the
metric's meaning).
Z= SGR substring for zero values.
S_TIME_FORMAT
If this variable exists and its value is ISO then the current lo-
cale will be ignored when printing the date in the report header.
The iostat command will use the ISO 8601 format (YYYY-MM-DD) in-
stead. The timestamp displayed with option -t will also be com-
pliant with ISO 8601 format.
EXAMPLES
iostat Display a single history since boot report for all CPU and De-
vices.
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.
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
https://sysstat.github.io/
Linux AUGUST 2023 IOSTAT(1)
Generated by dwww version 1.16 on Sat Oct 3 06:26:25 CEST 2026.