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The Red Hat Enterprise Linux landscape constantly changes, and version 7 of the platform offers additional features that can create new challenges for administrators.
Fortunately, certifications such as Red Hat Certified System Administrator (RHCSA) and Red Hat Certified Engineer (RHCE) ensure that admins are able to adapt and familiarize themselves with every new adjustment in the Red Hat Enterprise Linux (RHEL) platform.
In Red Hat RHCSA/RHCE 7 Cert Guide: Red Hat Enterprise Linux 7 (EX200 and EX300), a recent book by Sander van Vugt, a technology consultant and TechTarget contributor, admins learn concepts to prepare for both certification exams, including two of the biggest changes with the RHEL 7 -- GRUB 2 and systemd. Both features play a role in the Linux boot procedure.
Systemd is RHEL 7's new service manager that takes care of a variety of tasks. For example, it can start services, start jobs under specific conditions at specific times, initialize hardware and mount file systems, among other capabilities.
"Systemd is a major change between RHEL 6 and RHEL 7," van Vugt said. "It has taken over really everything that's happening with Red Hat Enterprise Linux."
The major benefit of systemd during the Linux boot procedure is that it provides a uniform management interface to start what's called units -- which can be services, sockets, mounts, devices or other components, according to van Vugt. But it also presents challenges, such as the risk of becoming overwhelmed with options to configure unit files. To understand systemd, you'll also need to master the concepts of target units and wants.
The role of GRUB 2 in the Linux boot procedure
While admins generally deal with systemd on a daily basis, GRUB 2 is only involved in the reboot process -- which can be about every two years for some Linux servers. However, this doesn't lessen the importance of understanding GRUB 2. If you don't fully understand GRUB 2, you can run the risk of causing severe damage to the system.
"As long as the boot procedure is done well, then everything is fine," van Vugt said. "But when a server starts and something doesn't go right and the boot procedure gets stuck, it requires some good insight."
Sometimes, admins will need to alter GRUB 2's configuration. In this case, van Vugt suggests the following process in Chapter 18: Managing and Understanding the Boot Procedure:
Normally, GRUB 2 works just fine and does not need much maintenance. In some cases, though, you might have to change its configuration. To apply changes to the GRUB 2 configuration, the starting point is the /etc/default/grub file. In this file, you'll find options that tell GRUB what to do and how to do it.
Apart from the configuration in /etc/default/grub, there are a few configuration files in /etc/grub.d. In these files, you'll find rather complicated shell code that tells GRUB what to load and how to load it. You typically do not have to modify it. You also will not need to modify anything if you want to make it possible to select from different kernels while booting. GRUB 2 picks up new kernels automatically and adds them to the boot menu automatically, so nothing has to be added manually.
To further explore the role of systemd and GRUB 2 in the Linux boot procedure, go to page 60 of this PDF to read Chapter 18 in its entirety.
Editor's note: The excerpt included above is from Red Hat RHCSA/RHCE 7 Cert Guide: Red Hat Enterprise Linux 7 (EX200 and EX300), authored by Sander van Vugt, published by PearsonITCertification, Sept. 2015.
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