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The manual page and help for the iostat Linux command. The iostat command is a tool for monitoring the input/output data transmission of the system's devices, which monitors the average transmission speed of the devices in relation to their active operating time. iostat prepares reports that can be used to optimize the system configuration to achieve balanced operation.
Man page output
man iostatIOSTAT(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 } ] [ -j { ID | LA‐
BEL | 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 re‐
lation 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 re‐
port. 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 de‐
vice 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 con‐
junction 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 gen‐
erates 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 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 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 de‐
vice. 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 sec‐
ond.
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 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.
-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).
-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. 1.0k, 1.2M, etc.) The units displayed with this option supersede any other de‐
fault 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, al‐
ways or auto (the latter is the default).
Note: On Debian sysstems the colors are displayed by default when output is connected to the terminal, even if this vari‐
able is not set (i.e. unset variable is treated as if it were set to auto).
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)
https://github.com/sysstat/sysstat
http://pagesperso-orange.fr/sebastien.godard/
Linux JULY 2018 IOSTAT(1)
Help output
iostat --helpHasználat: iostat [ kapcsolók ] [ <időköz> [ <darabszám> ] ]
Options are:
[ -c ] [ -d ] [ -h ] [ -k | -m ] [ -N ] [ -s ] [ -t ] [ -V ] [ -x ] [ -y ] [ -z ]
[ -j { ID | LABEL | PATH | UUID | ... } ]
[ --dec={ 0 | 1 | 2 } ] [ --human ] [ -o JSON ]
[ [ -H ] -g <group_name> ] [ -p [ <device> [,...] | ALL ] ]
[ <device> [...] | ALL ]
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