iostat

Report CPU statistics and input/output statistics for devices and partitions.

Description

The iostat command is used to monitor system input/output device loading by observing the time the devices are active in relation to their average transfer rates. It reports CPU utilization and disk activity statistics. Like vmstat, it provides a system-wide overview rather than per-process analysis.

iowait indicates the percentage of time that the CPU was idle during which the system had an outstanding disk I/O request.

Installation

iostat is part of the sysstat package.

For RedHat / CentOS / Fedora:

sudo yum install sysstat 

For Debian / Ubuntu / Linux Mint:

sudo apt-get install sysstat

Syntax

iostat [options] [interval [count]]

Options

-c         Display the CPU utilization report.
-d         Display the device utilization report (default).
-h         Make reports easier to read (human-readable).
-k         Display statistics in kilobytes per second.
-m         Display statistics in megabytes per second.
-t         Print the time for each report.
-V         Display version and exit.
-x         Display extended statistics.
-y         Omit the first report since boot if multiple intervals are displayed.
-z         Tell iostat to omit output for any devices for which there was no activity.
-j         Display persistent device names (ID, LABEL, etc.).
--human    Print sizes in human-readable format (e.g., 1.0k, 1.2M).
-o JSON    Display statistics in JSON format.
-H         Display only global statistics for groups.
-p         Display statistics for block devices and all their partitions.

Parameters

• interval: Time in seconds between reports.
• count: Number of reports to generate.

Examples

Example 1: Basic report

# iostat
Linux 4.18.0 (node1) 	08/28/2024 	_x86_64_	(2 CPU)

avg-cpu:  %user   %nice %system %iowait  %steal   %idle
           3.30    0.01    1.90    0.12    0.00   94.68

Device             tps    kB_read/s    kB_wrtn/s    kB_read    kB_wrtn
vda               7.85        84.22        36.59 1081853831  470049100

CPU Report Metrics:

• %user: CPU utilization at the user level.
• %nice: CPU utilization at the user level with nice priority.
• %system: CPU utilization at the system (kernel) level.
• %iowait: Time the CPU was idle with outstanding I/O requests.
• %steal: Time spent in involuntary wait by the virtual CPU.
• %idle: Time the CPU was idle with no outstanding I/O requests.

Device Report Metrics:

• Device: Name of the device or partition.
• tps: Transfers per second.
• kB_read/s: Data read from the device in kB/s.
• kB_wrtn/s: Data written to the device in kB/s.
• kB_read: Total kB read.
• kB_wrtn: Total kB written.

Example 2: Human-readable extended report, ignoring first report, every 1s for 5 times

# iostat -hdy 1 5

Example 3: Extended statistics

# iostat -xd 1

Extended Metrics:

• r/s: Read requests per second.
• w/s: Write requests per second.
• rrqm/s: Read requests merged per second.
• wrqm/s: Write requests merged per second.
• r_await: Average time (ms) for read requests to be served.
• w_await: Average time (ms) for write requests to be served.
• aqu-sz: Average queue length of requests.
• %util: Percentage of CPU time during which I/O requests were issued (bandwidth utilization).

When %iowait is high, pay attention to %util (close to 100% indicates a bottleneck) and await values.