The bootloader is a program that is executed by the BIOS after it completes its tasks of initializing the hardware and performing the POST (Power-On Self Test). The bootloader is responsible for loading the kernel and other necessary files into memory and passing control to the kernel. The bootloader can be either installed in the Master Boot Record (MBR) of the disk or in a separate partition. Some examples of bootloaders are GRUB, LILO, and SYSLINUX. References: LPI Linux Essentials - 1.101.1, LPI Linux Administrator - 102.1

/etc/inittab
Explanation
The system configuration file named /etc/inittab is commonly used to set the default runlevel. This file contains information about the initialization process of the system, and it defines the default runlevel, the available runlevels, and the actions to be taken when entering or leaving a runlevel. The default runlevel is the mode of operation that the system starts up into, and it determines which services and processes are running.
The default runlevel is specified by a line similar to the following in the /etc/inittab file:
id:5:initdefault:
The number after the first colon indicates the default runlevel, which can range from 0 to 6. The meaning of each runlevel is:
* 0 - Halt
* 1 - Single-user text mode
* 2 - Not used (user-definable)
* 3 - Full multi-user text mode
* 4 - Not used (user-definable)
* 5 - Full multi-user graphical mode (with an X-based login screen)
* 6 - Reboot
To change the default runlevel, edit the /etc/inittab file as root and change the number to the desired runlevel.
For example, to change the default runlevel to 3, use the following command:
sudo nano /etc/inittab
And change the line to:
id:3:initdefault:
Then save and exit the file. The changes will take effect on the next reboot.
References:
* SysV Init Runlevels - Red Hat Customer Portal
* init - How can I see or change default run level? - Ask Ubuntu

The Logical Volume Manager (LVM) is a tool that allows the creation and management of logical volumes on Linux systems. Logical volumes are partitions that can span multiple physical disks and can be resized or deleted without affecting the rest of the system. Some of the benefits of using LVM are:
* To dynamically change the size of logical volumes. LVM allows the user to increase or decrease the size of a logical volume without having to repartition the disk or reboot the system. This can be useful for allocating more space to a volume that is running out of space, or freeing up space from a volume that is not needed anymore.
* To create snapshots. LVM allows the user to create a snapshot of a logical volume, which is a copy of the volume at a certain point in time. Snapshots can be used for backup purposes, as they can be restored to the original volume if needed. Snapshots can also be used for testing purposes, as they can be mounted as read-only or read-write volumes without affecting the original volume.
* To dynamically create or delete logical volumes. LVM allows the user to create or delete logical volumes on the fly, without having to repartition the disk or reboot the system. This can be useful for creating temporary volumes for specific purposes, or deleting volumes that are no longer needed.
LVM cannot be used for the following purposes:
* To create RAID 9 arrays. RAID 9 is not a valid RAID level, and LVM does not support RAID functionality. RAID is a technique that uses multiple disks to provide redundancy, performance, or both. RAID can be implemented at the hardware level, by using a RAID controller, or at the software level, by using tools such as mdadm or dmraid. LVM can work on top of RAID devices, but it cannot create them.
* To encrypt logical volumes. LVM does not provide encryption functionality. Encryption is a technique that protects data from unauthorized access by using a secret key to transform the data into an unreadable form. Encryption can be implemented at the disk level, by using tools such as dm-crypt or LUKS, or at the file system level, by using tools such as eCryptfs or EncFS. LVM can work on top of encrypted devices, but it cannot encrypt them.
:
LPI Linux Essentials - Topic 3: Command Line Operations
LPI Linux Essentials - Topic 4: User Interfaces and Desktops
LPI Linux Essentials - Topic 5: Administrative Tasks
LPI Linux Essentials - Topic 6: Essential System Services
LPI Linux Essentials - Topic 7: Networking Fundamentals
LPI Linux Essentials - Topic 8: Security Fundamentals
LPI Linux Essentials - Topic 9: Basic Scripting
LPI Linux Essentials - Topic 10: IT Explorations
LPI Linux Essentials - Topic 11: Finding Your Way on a Linux System
LPI Linux Essentials - Topic 12: The Power of the Command Line
LPI Linux Essentials - Topic 13: The Linux Operating System
LPI Linux Essentials - Topic 14: Security and File Permissions
LPI Linux Essentials - Topic 15: Basic Linux System Administration
LPI Linux Essentials - Topic 16: Quotas
LPI Linux Essentials - Topic 17: Managing Users and Groups
LPI Linux Essentials - Topic 18: Ownership and Permissions
LPI Linux Essentials - Topic 19: Special Permissions and Attributes

renice
Explanation
The renice command changes the nice level of a running process. The nice level is a value that affects the scheduling priority of a process. A lower nice level means a higher priority and a higher nice level means a lower priority. The renice command requires the process ID (PID) of the target process and the new nice level as arguments. For example, renice -n 10 1234 will change the nice level of the process with PID 1234 to 10.
References: LPI Exam 101 Detailed Objectives, Topic 103: GNU and Unix Commands, Weight: 25, Objective 103.3: Perform basic file management, renice command