| IOSTAT(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 ] [ -j { ID | LABEL | 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 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.
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
%nice
%system
%iowait
%steal
%idle
- 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:
Note: In previous versions, this field was known as avgrq-sz and was expressed in sectors.
Note: In previous versions, this field was known as avgqu-sz.
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 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 default 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, 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 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:
- 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
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)
| JANUARY 2018 | Linux |