RHEL 7.2 officially released.

Today, Red Hat announces the official release of RHEL 7.2.

To know more about this new version you can read a summary of the RHEL 7.2 changes or the RHEL 7.2 Release Notes.

Also and at the same time, RHEL Atomic Host 7.2 is released with docker v1.8.2, kubernetes v1.0.3, flannel v0.5.3 and cockpit v0.77.

Finally, although Systemd has been updated in version 219 in RHEL 7.2, its development is still ongoing: yesterday saw the release of Systemd version 228.

Posted in RHEL7

Yum plugins.

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.

Posted in RHEL7

RHEL 7 Password recovery procedure.

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.

Posted in RHEL7

RHEL 7 Delta rpms.

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.

Posted in RHEL7

RHEL 7 Entropy mechanisms.

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.

Posted in RHEL7

RHEL 7 package group management.

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.

Posted in RHEL7

Happy birthday again!

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!

Posted in RHEL7

Time to play with SSL certificates.

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!

Posted in RHEL7

KVM thin provisioning tip.

If you use KVM for managing your virtual machines, you can sometimes run out of space in the /var/lib/libvirt/images directory, the default location for the RHEL/CentOS distributions.
Because KVM knows the concept of thin provisioning through the qcow2 image format, the one used by the virt-install command by default, it would be crazy not to use it.
This can be done through the virt-sparsify command coming with the libguestfs-tools rpm package. So, the virt-sparsify command copies a VM image, only keeping the necessary data.

Let’s try an example.
Install the libguestfs-tools package:

# yum install libguestfs-tools

Go to the /var/lib/libvirt/images directory (or the one that you are using for storing your VM images):

# cd /var/lib/libvirt/images

Choose a VM and stop it (here vm.example.com) (use the virsh destroy command if necessary):

# virsh shutdown vm.example.com

Execute the virt-sparsify command:

# virt-sparsify -q vm.example.com.img vm.example.com.img2

Note: The -q option removes any display (quiet). Don’t ask me why this is not the default!

Get the size of the VM before and after:

# du -k vm.*
8388660 vm.example.com.img
1370168 vm.example.com.img2

Note: The ls command doesn’t display the correct information.

Replace the old image with the new one:

# mv -f vm.example.com.img2 vm.example.com.img

Restart the VM:

# virsh start vm.example.com

As you can see, it’s quite simple! I’m sure you will love it!

Posted in RHEL7

RHEL Disk tip.

During the RHCSA exam, you need to go fast.
When dealing with partition creation, you can’t afford to waste time, searching for information about the current configuration with almost obsolete command like fdisk -l displaying a very cryptic and mostly useless information.
You need to use the right command before starting any disk operation.
This command is called lsblk and stands for LiSt BLocK devices.

# lsblk -a
vda           252:0    0    6G  0 disk 
├─vda1        252:1    0  390M  0 part /boot
└─vda2        252:2    0  5.5G  0 part 
  ├─rhel-swap 253:0    0  552M  0 lvm  [SWAP]
  └─rhel-root 253:1    0    3G  0 lvm  /

With the lsblk command, you get quickly the following information about the current disk configuration:

  • it is a virtual machine (vda, sda would indicate a physical server),
  • there is only one disk /dev/vda of 6GB,
  • the disk is divided into two partitions (vda1 and vda2) respectively with a size of 390MB and 5.5GB,
  • the vda1 partition is mounted under /boot,
  • the vda2 partition consists in two logical volumes (lvm) swap and root in a volume group called rhel,
  • the swap logical volume is used by the system as a swapping area ([SWAP]) of 552MB,
  • the root logical volume is mounted under / with a size of 3GB,
  • there is around 2GB of free available space (5.5GB552MB3GB=2GB) in the vda2 partition,
  • none of the partitions are in Read-Only mode (RO=0) or ReMovable (RM=0).

By default, the lsblk command skips empty devices. The -a option corrects this behaviour and displays all devices, empty ones included.

With only one command, you get almost everything you need!

Posted in RHEL7

RHCSA7: Task of the day

Allowed time: 10 minutes.
Boot and change the root password before the end of the boot process.

RHCE7: Task of the day

Allowed time: 10 minutes.
Set up a NFS server that exports the /opt directory in read-only mode.

Poll for favorite RHEL 7 book

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