The website is mainly about RHEL 7/CentOS 7 but the distribution running the webserver was still CentOS 6: something was wrong.
This week I have been busy migrating from a physical server on CentOS 6 to a much powerful virtual machine on CentOS 7.
I hope you will find the website more responsive.

Otherwise, we have seen Microsoft and Red Hat signing several agreements recently, something that most people thought they would never see. Even better, Microsoft started a new certification program around Linux on Azure!
Unbelievable!

Recently on Reddit, someone wrote:

[…]There are minor differences in command syntax when comparing CentOS and RHEL. For example, nmcli and the lvm management both functioned incorrectly I found when I was using the utilities extensively on CentOS (this is compared to what was advised in the RHEL course, and alongside my past knowledge of LVM, the errors being presented shouldn’t of occurred – and indeed didn’t when I tried repeated them on RHEL the following day).

[…]Perfect example is the following: You’ve got an existing connection named “System eth0”, and you plan to adjust the “ipv4.addresses” field to set an IP address and a gateway. In RHEL, you’d type the following:
nmcli connection modify “System eth0” ipv4.addresses “10.0.0.1/24 10.0.0.254”
This would set the first field as the IP, and the second as the gateway.

In CentOS however, you’ll get an error like the following:
“ERROR: 24 10.0.0.254 isn’t a valid prefix.”

Because many candidates intensively use CentOS for preparing their exams, I thought this question would deserve a clear answer. I asked Karanbir Singh, the lead developer for CentOS, via Twitter.
Here, what he answered:

that’s an incorrect assertion, NetworkManager / nmcli has been verified to have similar functionality.

Fabian Arrotin, a member of the CentOS team, also wrote:

difference between NetworkManager 0.9.9 from el 7.0 and then bumped to 1.0.0 in el7.1 ? (and RHCE course for 7.0) ?

I found Fabian‘s answer very interesting.

I launched two VMs, one in RHEL 7.0 and one in RHEL 7.1. I then checked the behaviour of the nmcli command. Here what I got:

On the RHEL 7.0 VM:

# nmcli con mod "System eth0" ipv4.addresses "192.168.122.80/24 192.168.122.254"
#

On the RHEL 7.1 VM:

# nmcli con mod "System eth0" ipv4.addresses "192.168.122.80/24 192.168.122.254"
Error: failed to modify ipv4.addresses: invalid prefix '24 192.168.122.254'; <1-32> allowed.

How could you say that CentOS doesn’t behave like RHEL when two versions of RHEL give different results? This is the version of NetworkManager that matters!

In the RHEL 7.0 case, you’ve got NetworkManager-0.9.9.1.
In the RHEL 7.1 case, it is NetworkManager-1.0.0.

I found one bug fix affecting the gateway syntax (rh #1170199: Unable to add static IP address with gateway) in the changelog between the two versions but there are perhaps more of them.

Conclusion1: Don’t use this kind of syntax any more:

# nmcli con mod "System eth0" ipv4.addresses "10.0.0.1/24 10.0.0.254"

Do it in two steps:

# nmcli con mod "System eth0" ipv4.addresses 10.0.0.1/24
# nmcli con mod "System eth0" ipv4.gateway 10.0.0.254

Conclusion2: It is rather easy to spread a wrong rumor, but this is no good for anyone!

Yum is already a very powerful tool. But it can still be enhanced through a plugin mechanism.

Besides the fastestmirror plugin that allows you to get the new packages from the quickest mirror, there are other plugins adding new features to the whole system like priorities between repositories or changelog messages.

Discover some of them through the yum plugin tutorial.

Everybody thinks the password recovery procedure in RHEL 7 is simple. But it is not.

To start with, there are several procedures spread all over the Internet. All are slightly different, all are supposed to run in all situations, with physical server and virtual machine. They aren’t.

Then, a RHCSA candidate not only has to know the procedure, he also has to be quick: wasting several minutes waiting for the autorelabel to run is not very efficient. Some enhancements exist to avoid this pitfall.

Finally, failure is not an option: several RHCSA candidates have experimented what it means to receive a zero score because they couldn’t make it.

Test this RHEL 7 password recovery procedure many times. Learn it by heart.
If something doesn’t work as expected, report it, even though it has been already tested hundred times by many people.

Last year there was a discussion whether delta rpms should be activated or not by default in the Fedora 22 distribution, whether this feature should be kept or simply removed.

But do you know exactly what delta rpms are? How do they work? What is the default behaviour? Which are the available parameters to change this default behaviour?

To improve your knowledge and decide whether to use them or not, read the delta rpms tutorial.

Sometimes to get some entropy you have to do strange things.

Do you remember to make sudden mouse movements during SSH keys generation?

Where do this entropy come from? Why does everything sometimes seem stopped? How does it work for a virtual machine?

These are some of the questions discussed in the Random Number Generator tutorial.

I’m sure you will learn something.

At first, managing package groups seems easy.

Package groups are a simple means to gather packages under a unique name.

But, it’s not so simple! There are different types of package groups. There are at least two ways to call them. When installing package groups, some packages are installed by default, some others aren’t.

Take two minutes and learn some subtleties about the package group management.

It’s now two years that this website exists.

New tutorials have regularly been added. Lots of tutorials have seen their content increased through the “Additional Resources” section to provide advanced material to hungry readers.

Besides learning new topics, keep an eye on your typing speed, because during an hands-on exam it can make a difference.

I hope you still enjoy this website!

Until recently, SSL certificates were so expensive that you couldn’t set up your personal website only for fun. You had to have a good reason or a big wallet.

This is not the case anymore. Now and until the letsencrypt.org initiative takes off, for a minimal price, you can start to play with standard or wildcard SSL certificates and get some experience with them.

If you are interested in, there is a full tutorial about setting up a SSL certificate on RHEL 7, including all the steps, from certificate purchase to certificate installation.

Auto-signed certificates are perhaps on the way out!