Basics

io interpretation

Layers of Linux Distribution

Linux Kernel

It handles system hardware resources on behalf of the OS user.

Linux Desktop

A software designed to manage graphical interface features like windows, menus, application controls..etc Eg: GNOME, Unity, KDE Plasma, Xfce, Cinnamon ..etc

Linux Distribution

Specific system tools like software package managers , process managers..

Example

  • Android
  • RedHat Enterprise Linux
    • CentOS
    • Fedora
  • Debian
    • Ubuntu
    • Kali Linux (Security)
    • Mint
  • Arch Linux
    • LinHES
    • Manjaro
  • SUSE
    • Open SUSE
  • Scientific Linux (Science & Maths)
  • Raspbian (Mini architectures) ..so on

Package managers

  • Debian : DPKG/ APT / snap
    • dpkg installs any .deb debian package. It will just list other dependencies .
    • apt/ apt-get is package manager which uses dpkg internally, it installs particular package & it's dependencies too.
    • snap is package manager to work across range of linux distributions, snapcraft store
  • Red Hat Linux : RPM/ YUM (DNF)
    • RPM like dpkg installs .rpm packages.
    • YUM is a package manager
    • DNF or Dandified YUM is the next-generation version of the YUM
  • SUSE (Zypp)
  • Arch Linux (Pacman)

How Linux Loads

OS Loads

  1. BIOS (Basic Input Output System)/ UEFI (Unified Extensible Firmware Interface)

    • BIOS is older, modern computers have UEFI
    • Both are low-level software that resides in a chip on your computer’s motherboard.
    • You can change boot order, system time & access hardware configuration
    • It wakes up your computer’s hardware components, ensures they’re functioning properly.

  2. BIOS/ UEFI looks for a Master Boot Record (MBR)/ GPT (GUID Partition Table) respectively, stored on the boot device and uses it to launch the boot loader

  3. GRUB (Grand Unified Bootloader)

    • Boot loader boots operating system
    • Similar to windows safe mode, in advanced -> kernel/ recovery mode exists. Login with it if any issues in main operating system.
    • Note:
      • in /boot -> core linux files exists like vmlinuz-4.15.0
      • Actual configuration /boot/grub/grub.cfg file shouldn't be changed directly. Instead use /etc/default/grub, /etc/grub.d for configuration.
      • Later run 'update-grub' to reflect those changes in /bott/grub/grub.cfg

Linux Run levels

May vary based on distributions

0 - system halt
1 - single user (rescue) mode
3 - multi user mode without GUI
5 - multi user with GUI
6 - reboot
//check existing
systemctl get-default (output is graphical.target)
//change
systemctl enable multi-user.target

File System Hierarchy

Filesystem_Hierarchy_Standard

Root Level Directories

  • /bin : Binary files for (single user mode) system commands
  • /sbin : Binary files for (multi-user) system commands //system bin
  • /boot : Linux images and boot configuration files
  • /dev : Pseudo files representing devices
  • /etc : Configuration files
  • /home : User files
  • /lib : Software library dependencies
  • /root : Root user files
  • /usr : Additional binaries
  • /var : Updating files: logs, application data, cache

Pseudo File Directories

(dynamic data created in these folders)

  • /proc : Files representing running system processes
  • /dev : Pseudo files representing devices
  • /sys : Data on system and kernel resources

Linux Desktops

  • GNOME
  • Cinnamon/ Mate
  • XFCE ..so on

Links

.profile , .bashrc & passwd

User Settings

//Following file has user environment profile (it also loads ~/.bashrc)
~/.profile
// Following file gets run when ever bash session is started
//It is used to load user terminal preferences, set environment variables, set custom alias commands
~/.bashrc
  • Bash is case sensitive
  • Use string quotes '' if command file has spaces, use escape \ char for any special chars

Global settings

//global profile setting
/etc/profile
//global .bashrc
/etc/bash.bashrc
//It has user's -> ID, GroupId, Home Directory & bash to be used
/etc/passwd

Note : In CentOS /etc/profile.d/custom.sh -> add variables