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Use Iotop To Locate High I/O on CentOS 6

Published on: Fri, Jan 22, 2016 at 1:27 pm EST
CentOS Linux Guides System Admin

If you are a Linux system administrator, one of your common maintenance tasks is to quickly determining which processes consume large amounts of disk I/O before you can find a solution accordingly.

You can use iotop to get this task done. Unlikeiostat, which can only display the summary of disk I/O, iotop can display the I/O usage of each process or thread. This will allow you to easily determine the most I/O consuming processes which are slowing down the system.

In this article, we will be covering the process of installing iotop on a CentOS 6 x64 server instance.

Prerequisites

Before further reading, you need to:

  • A Vultr instance running CentOS 6 x64.
  • A sudo user.

Install iotop

On CentOS 6, You can install iotop with the following command:

sudo yum install iotop

Launch iotop

For security purposes, non-root users who don't own sudo privileges have been forbidden to launch the iotop utility. You must be the root or a sudo user before you can launch the iotop:

sudo iotop

Use iotop

The iotop interface is rather intuitive. On the top of the screen, you can see the total disk read speed and the total disk write speed. then you can see a highlighted row of parameters explained as below:

  • PID: the process ID
  • PRIO: the I/O priority
  • USER: the user who is using the command
  • DISK READ: the disk output bandwidth
  • DISK WRITE: the disk input bandwidth
  • SWAPIN: the percentage of time the thread spent while swapping in
  • IO: the percentage of time the thread spent while waiting on I/O
  • COMMAND: the command name

Under the highlighted line, you can see all of the running processes in the system, sorted by one of the parameters mentioned above, one process a line.

You can use the following keys to control the display:

  • The left and right arrows: change the sorting column which by default is IO.
  • r: toggle the sorting order.
  • o: toggle between "only showing processes or threads actually doing I/O" and "showing them all".
  • p: toggle between "only showing processes, not all threads" and "showing processes and all threads".
  • a: toggle between "showing accumulated I/O" and "showing I/O bandwidth".
  • q: quit.
  • any another key: refresh.

This concludes our tutorial on how to install and use iotop. Thank you for reading.

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