Linux From Scratch.
Linux From Scratch (LFS) is a project that allows the user to build their own custom Linux system. Steps to build a Linux system from source codes are provided in the provided link above. LFS is a great way for users to learn how a Linux system works at its core. There are many packages and patches needed to do so, and they are provided on the website as well.
Why build a custom Linux system?
As mentioned above, utilizing LFS to build your own custom Linux system allows you to directly see how a Linux system works from the inside out. It also allows you to understand what constitutes a Linux system from the required packages and patches. Another thing to consider is that since the system is built by your own hands, you have the power to edit everything and apply whatever you want. This gives you freedom to do anything you want and also provides security protection to your data, since no one else has full access to your system.
Bootloaders
A bootloader is a specific piece of code that will always run whenever an operating system is being started. Every operating system will have a set of bootloaders specific for it that will always run before the operating system is allowed to run. It will usually contain several ways in which the operating system kernel can be booted and commands to debug and modify the kernel environment.
Bootloaders in Linux.
Most common Linux distributions will have one of three bootloaders, which are GRUB, GRUB2, and LILO. GRUB2 is mostly preferred as it is the most modern one. Whenever Linux is going through its boot sequence. The boot sequence happens whenever the machine is started up and finishes when the kernel is initialized. After the boot sequence is properly completed, systemd will start and the startup sequence begins. The startup sequence will shift Linux into its operational state.
systemd.
systemd is where all processes start from and it will be responsible to bring Linux into a working state. systemd will first mount the selected filesystems and access provided config files. These files are used to determine which state the machine should boot into. These config files are located in the mounted filesystem, in the /etc directory.
Firmware.
Firmware is a type of software that is stored on a flashable hardware device, such as EEPROMs. This is the opposite of regular softwares, which are stored in the disk. The firmware is at its core, a specific set of instructions that will be loaded into the hardware in order to be executed. The y usually provide instructions on how the device is able to communicate with other hardwares.
Controversies of systemd.
Although systemd sounds useful, there are many developers out there that dislike it. It was first introduced as a method to improve bootup times and improve loggings. Opinions on this matter differ however, as some people report that systemd does allow faster bootup times, while other people report no differences at all. While this change should not matter if nothing is affected, it is only true if systemd itself is not inflexible and convoluted to maintain. Most Linux users still prefer the older methods to boot, such as SysVInit and BSD init. With more and more versions of Linux adapting systemd, many people has had to change their systems to adapt systemd as well.
# systemctl start [name.service] –> used to start a specific service.# systemct1 stop [name.service] –> used to stop a specific service.# systemctl restart [name.service] –> used to restart a specific service.# systemct1 reload [name.service] –> used to reload a specific service.$ systemct1 status [name.service] –> displays the current status of a specific service.# systemctl is-active [name.service] –> checks whether a specific service is active or not.$ systemctl list-units --type service --all –> displays all units available.