# iostat - Report Central Processing Unit (CPU) statistics and in... - man(1) - [phpMan] > **TLDR:** Report statistics for devices and partitions. > - Display a report of CPU and disk statistics since system startup: `iostat` - Display a report of CPU and disk statistics with units converted to megabytes: `iostat -m` - Display CPU statistics: `iostat {{-c|--compact}}` - Display disk statistics with disk names (including LVM): `iostat -N` - Display extended disk statistics with disk names for device "sda": `iostat -xN {{sda}}` - Display incremental reports of CPU and disk statistics every 2 seconds: `iostat {{2}}` *Source: tldr-pages* --- [_IOSTAT_(1)](https://www.chedong.com/phpMan.php/man/IOSTAT/1/markdown) Linux User's Manual [_IOSTAT_(1)](https://www.chedong.com/phpMan.php/man/IOSTAT/1/markdown) ## NAME iostat - Report Central Processing Unit (CPU) statistics and input/output statistics for de‐ vices and partitions. ## SYNOPSIS ### iostat [ -c ] [ -d ] [ -h ] [ -k | -m ] [ -N ] [ -s ] [ -t ] [ -V ] [ -x ] [ -y ] [ -z ] [ **--compact ] [ --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_ **] ]** ## 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 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_ sec‐ onds 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 dis‐ played 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_ direc‐ tory. 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 com‐ bined 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 de‐ vice. d/s The number (after merges) of discard requests completed per second for the de‐ vice. f/s The number (after merges) of flush requests completed per second for the de‐ vice. 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 sec‐ ond. 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 de‐ vice. %rrqm The percentage of read requests merged together before being sent to the de‐ vice. %wrqm The percentage of write requests merged together before being sent to the de‐ vice. %drqm The percentage of discard requests merged together before being sent to the de‐ vice. areq-sz The average size (in kilobytes) of the I/O requests that were issued to the de‐ vice. 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. ## OPTIONS ### -c ### --compact Don't break the Device Utilization Report into sub-reports so that all the metrics get displayed on a single line. ### -d ### --dec={ 0 | 1 | 2 } Specify the number of decimal places to use (0 to 2, default value is 2). ### -f **+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 op‐ tion **+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 user‐ space. 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 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 dis‐ played 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 -g the group are to be displayed, and not statistics for individual devices in the group. ### -h --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 | ... } [ Display persistent device names. Keywords **ID**, **LABEL**, etc. specify the type of the per‐ sistent 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 ### -m ### -N 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 [ { 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, in‐ cluding 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. 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 display (use **--compact **option to prevent this). ### -s screens. ### -t of the **S_TIME_FORMAT **environment variable (see below). ### -V ### -x ### -y given interval. ### -z 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** By default statistics are displayed in color when the output is connected to a termi‐ nal. 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 in‐ dicates 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 com‐ pliant 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. 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 orange.fr) ## SEE ALSO [**sar**(1)](https://www.chedong.com/phpMan.php/man/sar/1/markdown), [**pidstat**(1)](https://www.chedong.com/phpMan.php/man/pidstat/1/markdown), [**mpstat**(1)](https://www.chedong.com/phpMan.php/man/mpstat/1/markdown), [**vmstat**(8)](https://www.chedong.com/phpMan.php/man/vmstat/8/markdown), [**tapestat**(1)](https://www.chedong.com/phpMan.php/man/tapestat/1/markdown), [**nfsiostat**(1)](https://www.chedong.com/phpMan.php/man/nfsiostat/1/markdown), [**cifsiostat**(1)](https://www.chedong.com/phpMan.php/man/cifsiostat/1/markdown) _ _ Linux SEPTEMBER 2021 [_IOSTAT_(1)](https://www.chedong.com/phpMan.php/man/IOSTAT/1/markdown)