Python dependency hell.

At the beginning there was the Bourne Shell. Then, Perl was created to better deal with character strings and regular expressions.

Linux came and the Bourne Shell was replaced with Bash (Bourne Again SHell) with many built-in features like integer arithmetic.

Because of its unusual syntax and its lack of object-oriented capabilities, Perl is now replaced with Python.

Today, Python is almost everywhere: tools like yum, tuned or Firewalld are all written in Python.

As the CPAN (Comprehensive Perl Archive Network) offered an incredible number of modules for Perl, Python modules have also been created to provide additional features.

They can be installed through RPM packages or with the pip install command.

Here is a potential problem. When you install a Python module through an RPM package, you get all the work done by the maintainer behind (RedHat, CentOS, EPEL, etc) to make sure that this module and all its dependencies will work fine together.

On the contrary, when you run the pip install command, you don’t know where the Python module will be installed and what exact dependency will be activated. In my experience, this doesn’t work very well. You can get the same Python module in different versions on the same server. In this situation, everything becomes very complicated. And this is not a RHEL/CentOS specific problem but concerns most of the Linux distributions (see details for Ubuntu here).

Furthermore, the pip install method sometimes requests that you compile modules locally. To compile Python modules, you need to install the gcc compiler: this is not a good practice in a production environment.

Conclusion: If you are not an expert in Python, stay away from the pip install command.

Posted in Others

New interesting articles.

There were several interesting articles recently published:

Happy reading!

Posted in Others

Happy new year 2017!

This week was the opportunity for two new tutorials:

I wish you a happy new year 2017 and a lot of success in everything you try!

Posted in Others

Merry Christmas!

Several very interesting articles were recently posted by Red Hat employees:

In addition, after a few months without any new tutorials (but with updates on existing ones), three new tutorials have been written:

I wish you a Merry Christmas!

Posted in RHEL7

CentOS 7.3 released.

More than a month after the announcement of RHEL 7.3, it is now time for the release of CentOS 7.3, also called CentOS 7 (1611).

In the Releases Notes appear the following major changes:

  • Support for the 7th-generation Core i3, i5, and i7 Intel processors and I2C on 6th-generation Core Processors has been added.
  • SHA2 is now supported by OpenLDAP.
  • ECC-support has been added to OpenJDK-8, PerlNet:SSLeay and PerlIO::Socket::SSL.
  • Bluetooth LE is now supported.
  • virt-p2v is now fully supported. virt-v2v and virt-p2v add support for the latest windows releases.
  • Lots of updated storage, network and graphics drivers.
  • Technology Preview: Among others support of Btrfs, OverlayFS, CephFS, DNSSEC, kpatch, the Cisco VIC and usNIC kernel driver, nested virtualization with KVM and multi-threaded xz compression with rpm-builds.

At least two serious issues have already been reported:

  • SElinux received major changes in this release, which might break certain functionality on your system.
  • The 4 STIG Security Profiles in the anaconda installer produce a broken sshd_config that must be edited before sshd will start (BZ 1401069).

The CentOS 7 (1611) distribution can be downloaded here as usual.

Posted in RHEL7

Main reasons for failure at the RHCSA exam.

Through this website I get feedback from many people taking Red Hat exams.

Hopefully, concerning the RHCSA exam, a lot of them pass it with flying colors but some fail too. So I get a good idea of the reasons why failure happens.

Without breaking any Non-Disclosure Agreement, I wrote an article for future candidates about the three main reasons causing failure.

I invite you to discover them here.

Posted in RHEL7

New book about KVM.

Until now there was almost no book about KVM in English. This lack is fulfilled.

Three people, working for Red Hat, have published a book called Mastering KVM Virtualization in August and this book provides an extensive coverage of this technology.

So, you will learn the basic stuff like the various ways to set up the network and the storage parts. But you will also get best practices, some performance tuning tips or some advanced configurations with OpenVswitch and oVirt.

This book is the new reference on this topic.

Posted in Others

RHEL 7.3 Firewalld new features.

From RHEL 7.0 to RHEL 7.2, Firewalld didn’t really evolve (v0.3.9.7 -> v0.3.9.14). It was mainly a matter of bug fixes.

As usual with RedHat, Systemd already showed it, new Firewalld features are triggered by backport difficulties: as new bugs are found, fixes are applied but, at some point, this becomes too difficult to maintain, upgrade to a complete new software version is necessary, bringing a new set of features as an additional bonus.

The new version of Firewalld (v0.4.3.2) included in RHEL 7.3 comes with the following features:

  • performance improvements: Firewalld starts and restarts significantly faster thanks to the new transaction model which groups together rules that are applied simultaneously.
  • ebtables support: tables of rules similar to iptables but for Ethernet frames, ebtables, are now supported and can be used in direct chains and rules.
  • better zone management: zone settings (connections, interfaces and sources) can be specified in NetworkManager, in Firewalld or in the ifcfg files.
  • ipset support: ability to create a set of IP addresses or networks used as zone sources, within rich and direct rules.
  • MAC address management: ability to specify a MAC address to define a source.
  • new firewall-cmd options: –info-zone displays details about a given zone, –info-service about a given service and –info-ipset about a given ipset.
  • easier troubleshooting: with the new LogDenied directive in the /etc/firewalld/firewalld.conf file, the user can easily debug and log denied packets.

As usual, the Firewalld dedicated page has been updated with the new available features and lots of details.

Posted in RHEL7

RHEL 7.3 officially released.

Yesterday, Red Hat announces the official release of RHEL 7.3.

To know more about this new version you can read a summary of the RHEL 7.3 changes or the RHEL 7.3 Release Notes.

Be careful when upgrading to RHEL 7.3, a problem can happen concerning the network interface names preventing the interfaces from working after reboot. Hopefully, the fix is simple and already available (see details).

Posted in RHEL7

New RedHat Summit 2016 videos.

It’s more than three months after the event that RedHat publishes some new videos.

And we are talking about 60 videos!

People like me, who were disappointed by the lack of good technical videos right after the event, can now uncover the real reason: due to the number of recorded sessions during the summit, some were not released and were almost forgotten by the subcontracting production company.

Among these videos, we will find:

You can watch all these videos and fitfty others on the RedHat Summit channel on Youtube and get the associated pdfs by searching for the presentation name here.


Posted in RHEL7

RHCSA7: Task of the day

Allowed time: 15 minutes.
Get an iso image of CentOS 7 (or a DVD) and set up a local repository.

RHCE7: Task of the day

Allowed time: 5 minutes.
Set up time synchronization with default configuration.

Poll for favorite RHEL 7 book

What is your favorite RHEL 7 book to prepare RHCSA & RHCE exams?

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Poll for most difficult RHCSA 7 topic

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Poll for most difficult RHCE 7 topic

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