The boot system is the process that occurs when a computer is powered on, starting from the hardware initialization until the operating system is loaded and ready to use. System management focuses on managing various hardware and software components to ensure the system runs smoothly. One of the key parts of the boot process is GRUB (Grand Unified Bootloader), which is responsible for loading the operating system.
The booting process consists of the steps that occur from the moment the computer is powered on until the operating system starts. This process is divided into two main phases: Initial Booting (BIOS/UEFI) and Operating System Booting.
BIOS (Basic Input/Output System) is the first firmware software that runs when the computer is turned on. BIOS is responsible for performing a hardware check (POST - Power On Self Test) and initializing hardware components such as the CPU, RAM, and storage devices.
UEFI (Unified Extensible Firmware Interface) is a more modern replacement for BIOS, offering advanced capabilities such as faster booting, support for large drives, and a graphical interface. Once BIOS or UEFI completes the hardware check, it looks for a valid boot device (e.g., hard drive, SSD, or USB drive).
After BIOS/UEFI finds a valid boot device, it loads the bootloader. In Linux systems, GRUB is the most commonly used bootloader.
GRUB is a bootloader used in many Linux distributions to load the operating system kernel. GRUB is responsible for selecting and loading the operating system to be run. There are two main versions of GRUB: GRUB Legacy (older version) and GRUB 2 (newer and more advanced version).
Selecting the Operating System: GRUB allows users to choose between multiple installed operating systems on a computer. This is particularly useful for dual-boot configurations (e.g., Linux and Windows).
Loading the Kernel: GRUB loads the Linux kernel into memory and hands over control to the kernel to continue the booting process.
Loading the Initrd File: GRUB also loads initrd (initial RAM disk), which contains necessary system files for the boot process before the main file system is used.
The GRUB configuration is located in the /etc/default/grub file (for GRUB 2). Some important parameters that can be configured include:
GRUB_DEFAULT: Specifies the default entry to be selected during boot.
GRUB_TIMEOUT: Specifies the duration GRUB waits before automatically booting.
GRUB_CMDLINE_LINUX: Specifies kernel parameters to be passed during booting.
After making changes to the GRUB configuration file, update GRUB with the command:
sudo update-grubGRUB provides a boot menu that allows users to choose the operating system or kernel to be loaded. This menu appears if there is more than one entry in the GRUB configuration, such as in a dual-boot system. Users can navigate the menu using arrow keys and press Enter to initiate booting.
System management focuses on managing and maintaining the operating system and hardware to ensure optimal performance and security. Some key system management tasks include:
Services are programs that run in the background to support system operations. In Linux, service management is performed using systemd (on modern distributions) or init.d (on older distributions). Systemd is a modern initialization and service manager used in many Linux distributions. Commonly used commands for managing services with systemd include:
Displaying service status:
systemctl status service_nameEnabling a service to run automatically at boot:
sudo systemctl enable service_nameDisabling a service:
sudo systemctl disable service_nameStarting a service:
sudo systemctl start service_nameStopping a service:
sudo systemctl stop service_nameSystemd is a modern initialization system used by many Linux distributions to manage processes and services. Systemd replaces older initialization systems like SysVinit with a faster, more parallel, and more flexible approach.
The initialization process with Systemd begins after the bootloader (such as GRUB) loads the Linux kernel. The steps are as follows:
Kernel is initialized: The kernel loads hardware drivers and activates the root file system.
Systemd starts: The kernel starts Systemd as the first process (PID 1).
Systemd reads unit files: Systemd reads configuration files called unit files, which define services, sockets, mount points, and more.
Services are started: Systemd starts services and processes based on defined dependencies.
Unit files are configuration files used by Systemd to manage various system resources. Unit files are typically located in:
/lib/systemd/system/: System default unit files.
/etc/systemd/system/\*\*: User-modified or added unit files.
Types of Unit Files:
Service (.service): For services.
Target (.target): For service groups (similar to runlevel in SysVinit).
Socket (.socket): For inter-process communication.
Mount (.mount): For mounted file systems.
Starting a Service
sudo systemctl start service_name.serviceStopping a Service
sudo systemctl stop service_name.serviceRestarting a Service
sudo systemctl restart service_name.serviceReloading Service Configuration
If you only want to reload the configuration without stopping the service:
sudo systemctl reload service_name.serviceEnabling a Service
To enable a service to start automatically at boot:
sudo systemctl enable service_name.serviceDisabling a Service
To disable a service from starting at boot:
sudo systemctl disable service_name.serviceChecking Service Status
To check the status of a service:
systemctl status service_name.serviceJournalctl is a built-in Systemd tool for viewing system logs. All logs managed by Systemd are stored in the journal. Basic journalctl commands:
Display all logs:
JournalctlDisplay the latest logs:
journalctl -fDisplay logs for a specific service:
journalctl -u service_name.serviceDisplay logs based on time:
journalctl --since "2025-01-01" --until "2025-01-08"View journal log size:
journalctl --disk-usageClean up journal logs:
sudo journalctl --vacuum-size=100MRsyslog is a traditional logging system used to store logs in text files, such as /var/log/syslog or /var/log/messages.
Rsyslog Configuration:
Main configuration file:: /etc/rsyslog.conf.
Additional configuration directory2: /etc/rsyslog.d/.
Basic Rsyslog Commands :
Start the Rsyslog service:
sudo systemctl start rsyslogStop the Rsyslog service:
sudo systemctl stop rsyslogCheck Rsyslog logs:
tail -f /var/log/syslogSystem maintenance involves software updates, disk space management, and system performance monitoring.
System Updates
For Debian-based distributions (Ubuntu, Debian):
sudo apt update && sudo apt upgradeFor Red Hat-based distributions (CentOS, Fedora):
sudo yum updateCleaning Up Disk Space
Remove unnecessary packages:
sudo apt autoremoveClean package cache:
sudo apt cleanMonitoring Disk Usage
View disk usage:
df -hCheck large files or directories:
du -sh /path/to/directoryPatching is the process of updating software to fix bugs or security vulnerabilities.
Automating Patching
On Ubuntu, use unattended-upgrades for automatic updates:
sudo apt install unattended-upgrades
sudo dpkg-reconfigure unattended-upgradesKernel Updates
The Linux kernel is frequently updated to fix bugs and improve security. Kernel updates can be performed as follows:
Ubuntu/Debian :
sudo apt install linux-genericCentOS/RHEL :
sudo yum update kernel