TuneD

Recently I had someone 'in the field' make a comment that one of our servers was not optimized to send video.

I reported this comment back to the Principal Engineer, who informed me that he had installed a package called TuneD on the server, which - depending on how it is configured of course - handles the automatic activation of certain "profiles"; each having a set of optimization parameters.

I looked into this. Sure enough, I found 2 directories; /etc/tuned and /usr/lib/tuned.

The /etc/tuned/ directory contains the main, or high level, configuration file (tuned.conf).

In the /usr/lib/tuned directory contains a list of individual system profiles. On the system I looked at, it appeared that the default profiles (provided by the tuned packagers) were included - which is probably a good thing if you then proceed to examine each of these profiles.

Inside /usr/lib/tuned, a file exists for each individual profile. So for example, in a "balanced" profile, if one were to peek inside of it with an editor (it is a text file), one would see a number of sysctl kernel parameters with specific values that get set when that profile is activated.

The tuned package uses a command line administrative tool called "tuned-adm" to get things done. It is quite simple, actually. Arguments include "off" (disable), "list" (list profiles), "active" (show the active profile"), and even "recommended" to show the recommended profile. If the system is not configured to automatically activate a profile, or a particular profile happens to be excluded due to policy, what is recommended might not be what happens to be active!

You can also create or modify profiles with the tuned-adm tool.

A useful link to get acquainted with the tool can be found at:

https://access.redhat.com/documentation/en-US/Red_Hat_Enterprise_Linux/6/html/Power_Management_Guide/tuned-adm.html

Multi-NIC - Multiple Default Routes

I am in the process of studying Multi-NIC; a process by which with two external ISP network adaptors, you can leverage both of those adaptors to distribute traffic in a bandwidth aggregation model.

I came across this article:
https://kindlund.wordpress.com/2007/11/19/configuring-multiple-default-routes-in-linux/

I configured this, and indeed, it seems to work, but need to do more testing with it.

Firewalld

People are starting to use this Firewalld.

I needed to get a quick understanding of it, and found this particular link a good starting point:

https://www.digitalocean.com/community/tutorials/how-to-set-up-a-firewall-using-firewalld-on-centos-7

DNS Resolution

Learned a lot about DNS resolution today, watching a colleague debug and configure this.

Need to look more into this.

AlienVault - Ossim

Downloaded the ISO for this today. I'll be playing around with this to see what it's all about.

KVM Virtualization - Initial Install

The site I chose to use to get guidance on the installation was:

http://www.itzgeek.com/how-tos/linux/centos-how-tos/install-kvm-qemu-on-centos-7-rhel-7.html

Pretty decent site.

After running the installation, I realized I needed to run virt-viewer to get things going, but immediately ran into the following error:

"virt-viewer undefined symbol g_type_check_instance_is_a fundamentally a"

In searching for a fix for this, I found a thread, and one of the suggestions was to try reinstalling virt-manager, by doing "yum reinstall virt-manager".
https://www.centos.org/forums/viewtopic.php?t=4175

After I did this, virt-manager seemed to work just fine and came up.

I then selected my virtual machine, and tried to power it up. It failed during boot with a "no bootable device" error. So, another search provided the fix for this problem, which was to go into device settings and change the image type to raw, from qcow. I guess kvm expects people to load qcow images by default.

https://azitech.wordpress.com/2011/07/23/no-bootable-device-on-kvmqemu/

The next issue I ran into, was again another boot issue. It looks like it tried to boot from DVD, then from ROM (looked like it worked), and then tried to boot from a floppy? That's where I am now (screenshot below).



Finally, I went back and noticed that my ISO image was 0 bytes. So I deleted the VM entirely, re-copied the ISO, and ran the "Install New VM" process again, with the option to do advanced configuration before installing (checkbox) selected.

This time, I did a couple of things that I didn't do before (I had overlooked them before). On the prompt where it says "Automatically detect operating system based on install media", I unchecked that box, selected Linux, and chose Red Hat 6.6. I then went into Boot Options and checked the box for Boot Menu, and unselected both the IDE Disk as well as ISO Image.  When I did this, and clicked the button to kick off the Install.

This time, I got the blue CentOS bootup screen.

UPDATE:
I could never get a new CentOS VM to install / load on this laptop I was using (HP older version with 4Gb RAM). I finally installed KVM on a more powerful Dell Precision T1700 server, and we'll see how it works on this. Actually, there is no X installed on this server, which means that I will need to run the GUI from the HP laptop, but the KVM host itself will be on this more powerful server.

D-Bus

I was reading up on FirewallD (separate post altogether forthcoming), and noticed it was based on D-Bus, which is an interprocess communication mechanism.

I thought I was aware of all of the interprocess communication mechanisms, but this one is more recently developed.

Looks like I have some reading to do in order to get current on this.