How to Check Memory and I/O with vmstat on Linux CentOS 5/6, RHEL 5/6 Server

The vmstat command is a powerful utility that provides valuable insights into processes, memory, I/O, and CPU activity on your Linux server. This tool is essential for server administrators who need to monitor and optimize system performance.

This tutorial will guide you through understanding and using vmstat on Linux CentOS 5 and CentOS 6, RHEL 5 and RHEL 6 servers to enhance your system’s performance.

Check Memory Command

When you execute the vmstat command without any arguments, it presents an output that might seem complex at first glance.

[root@rhel6 ~]# vmstat
procs -----------memory---------- ---swap-- -----io---- --system-- -----cpu-----
 r  b   swpd   free   buff  cache   si   so    bi    bo   in   cs us sy id wa st
 0  0      0 888252  28976  63004    5    0     0    11   15   18  0  0 99  0  0

The output of the vmstat command is divided into several sections, each providing information about a different aspect of your system’s performance. To understand the output, it’s crucial to understand what each field represents.

Understanding the vmstat Output

The output of the vmstat command is divided into six main sections: procs, memory, swap, io, system, and cpu. Each section provides different insights into your system’s performance.

Procs Fields

  • Waiting for run time (r)
  • Blocked (b)
  • Swapped out (w)

Memory Fields

  • Swap memory
  • Free memory
  • Buffered memory
  • Cached memory
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Swap Fields

  • Swapped in from disk (si)
  • Swapped out to disk (so)

IO Fields

  • Sent to block devices (bi)
  • Received from block devices (bo)

System Fields

  • Interrupts per second (in)
  • Context switches per second (cs)

CPU Field

  • User time (us)
  • System time (sy)
  • Idle (id) time

Using the vmstat Command

To print the vmstat version, run the following command:

vmstat -V

For example:

[root@rhel6 ~]# vmstat -V
procps version 3.2.8

You can set vmstat to run automatically by executing the following command:

vmstat nsec

Where nsec is the number of seconds you want it to wait before another update. For example, to run vmstat every 10 seconds, you would use:

vmstat 10

For example:

[root@rhel6 ~]# vmstat 10
procs -----------memory---------- ---swap-- -----io---- --system-- -----cpu-----
 r  b   swpd   free   buff  cache   si   so    bi    bo   in   cs us sy id wa st
 0  0      0 888072  29088  63004    4    0     0    11   14   18  0  0 99  0  0
 0  0      0 888064  29088  63004    0    0     0     0   12   15  0  0 100  0  0
 0  0      0 888064  29088  63004    0    0     0     0   13   16  0  0 100  0  0

There are several other useful vmstat usage options, such as:

vmstat [-V] [-n] [delay [count]]

-V prints version.
-n causes the headers not to be reprinted regularly.
-a print inactive/active page stats.
-d prints disk statistics
-D prints disk table
-p prints disk partition statistics
-s prints vm table
-m prints slabinfo
-t add timestamp to output
-S unit size
The delay is the delay between updates in seconds, and count is the number of updates.

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Commands Mentioned

  • vmstat – Provides information about processes, memory, I/O, and CPU activity
  • vmstat -V – Prints the vmstat version
  • vmstat nsec – Sets vmstat to run automatically, with nsec being the number of seconds between updates
  • vmstat 10 – Runs vmstat every 10 seconds

Conclusion

The vmstat command is a powerful tool for server administrators who need to monitor and optimize system performance. Understanding the output of vmstat and knowing how to use it effectively can help you keep your Linux CentOS 5/CentOS 6/RHEL 5/RHEL 6 server running smoothly. Whether you’re checking memory usage, monitoring I/O, or tracking CPU activity, vmstat provides the insights you need to optimize your system’s performance.

For more in-depth information about server optimization and performance, check out our articles on the best web servers, Apache, Nginx, and LiteSpeed servers. If you’re considering different hosting options, we also have comprehensive guides on dedicated server, VPS server, cloud hosting, and shared hosting.

Remember, maintaining optimal system performance is crucial for the smooth operation of your server. Regularly monitoring your system’s performance using tools like vmstat can help you identify potential issues before they become problems. Stay informed, stay proactive, and keep your server performing at its best.

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Frequently Asked Questions

  1. What is the vmstat command used for?

    The vmstat command is a utility in Linux that provides information about system processes, memory, I/O, and CPU activity. It is used to monitor and optimize system performance.

  2. How can I check the version of vmstat installed on my system?

    You can check the version of vmstat installed on your system by running the command ‘vmstat -V’.

  3. How can I set vmstat to run automatically?

    You can set vmstat to run automatically by executing the command ‘vmstat nsec’, where nsec is the number of seconds you want it to wait before another update.

  4. What does the ‘procs’ field in the vmstat output represent?

    The ‘procs’ field in the vmstat output shows the number of processes that are waiting for run time, blocked, or swapped out.

  5. What does the ‘memory’ field in the vmstat output represent?

    The ‘memory’ field in the vmstat output shows the kilobytes of swap memory, free memory, buffered memory, and cached memory.

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