LPIC-1 #

About Linux #

• Components of Linux

  • Boot Loader
    • Software manages boot process till the OS starts to load
  • The Kernel
    • Core of OS, manages OS, CPU and peripherals
  • Daemons
    • Processes lurking in the background that start during booth or after login (e.g. time)
  • Shell
  • Graphical Server
    • Subsystem to display graphic
    • AKA x-server
  • Desktop Environment
    • Actual GUI for the user
  • Applications

• Why Linux ?

  • Free
  • Stable
  • Secure
  • Open Source
    • Free to run the program for any purpose.
    • Free to study how the program works
    • Free to change how the program works
    • Free to redistribute copies

• Distributions

  • What is a distribution ?
    • Collection of software
    • Package management system
    • Helps you install, upgrade and remove software
    • Keeps your server up to date
  • Popular Examples
    • Red Hat
      • CentOS (based on red hat)
      • Fedora
    • Debian
      • Ubuntu
      • Mint
    • SuSE
    • Gentee
    • Arch
    • …

• VirtualBox Bridged Networking

  • If you do this, instead of NAT, you can SSH into the box instead of using the VirtualBox UI

System Architecture #

• Boot the system

  • UEFI is the new version of BIOS
    • BIOS booting
      • -> BIOS boot from particular disk
      • -> This disk has a MBR (Master Boot Record), which stores the Boot Loader
      • -> The boot loader knows where the kernel is on disk and boot the OS
    • UEFI
      • UEFI Boot Loader (which lives on your disk) (is not in the MBR)
      • This boot loader calls the kernel, which boots the OS
  • MBR : Information in the first sector of a disk that tells where and how the OS is.
  • GRUB (Grand Unified Bootloader) : Boot loader package that supports multiple OS’s on a ps
    • You can modify the settings during bootup and make them persist by directly modifying the config files used by the GRUB
    • For Ubuntu in VirtualBox, tap esc during bootup
  • Kernel is lowest level of replacable software to your hardware
  • Once the Kernel has attached the root file system, it will run a program called init
  • init is always the first process ran by a linux system, therefor, it gets always a PID of 1
    • There are a few different init programs that exist
      • sysvinit : Which based on sysv, oldest and first
      • systemd : Low memory boot process, mainstream, almost used everywhere now
      • upstart : Created by Ubuntu, but they switched to systemd in the end.
  • quiet for kernel param is supress most boot messages. So less verbosity for bootup

• Determine and configure hardware settings

  • udev : Device manager for your kernel
    • Gives low level access to the linux device tree
    • Handles user space events (happens when hardware is removed or added to the system)
      • Eg. Loading firmware
    • Provided by temporary filesystem (tmpfs)
      • This is how udev provides access, which is mounted to /dev on startup
    • /etc/udev/rules.d : Folder for custom rules for the device manager udev.
      • You can create rules for what should happen/ran when something is plugged in or unplugged
  • dbus
    • Inter-process communication mechanism
    • Framework that allows processes to talk to each other
    • Secure
    • Reliable
    • Provides high level OOP interface
  • sysfs
    • Virtual filesystem
    • Presents information about various kernel subsystems
      • Hardware devices
      • Drivers
    • Mounted to /sys
  • procfs
    • Similar to sysfs
    • Presents information about various processes
    • Presents information about system information
    • mounted to /proc
      • Can be used to interface with the kernel
      • Change parameters on the fly
    • Each running process will have a directory in /proc/<PID> + various other stuff
      • eg. /proc/cmdline -> Kernel name from bootup
      • eg. /proc/version -> Kernel version
      • eg. /proc/cpuinfo -> CPU info
  • lsmod
    • List all Kernel modules in use and by which modules
  • modprobe
    • Add or remove loadable kernel modules to/from the kernel
    • udev relies upon modprob to load drivers for automatically detected hardware
  • rmmod
    • Remove kernel module (prob need root for that)
  • lspci
    • Shows all PCI connected devices to the system
    • Show Device IRQ settings

• Runlevels and boot targets

  • Run Level : Number between 0 <-> 6 (max 9), determines which scripts/programs are run
    • Levels :
      • 0 - Halt or shut down system
      • 1 - Single user mode
      • 2 - Multi user mode without networking
      • 3 - Normal boot (multi user mode + networking)
      • 4 - Unused/customizable
      • 5 - Run level 3 + GUI display manager (if installed, so the graph env)
      • 6 - Reboot
    • Based on the run level, more or less scripts will be ran which are located in different places (e.g. Systemd or sysv)
      • inittab (came with sysv)
      • Ubuntu : /etc/rc0.d … /etc/rc6.d folders with scripts that are ran based on correlating run level. rcS.d us ran for any run level.
        • This is still there for compatibility reasons
      • systemd run levels :
        • Also has scripts
        • System scripts /etc/systemd/system
        • Package Scripts /usr/lib/systemd/system
        • /etc/systemd/system takes precedence over /usr/lib/systemd/systen
        • Uses targets (similar-ish to the other run level style)
          • Run Level - Systemd Target
          • 0 - runlevel0.target, poweroff.target
          • 1 - runlevel1.target, rescue.target
          • 2,4 - runlevel2.target, runlevel4.target, multi-user.target
          • 3 - runlevel3.target, multi-user.target
          • 5 - runlevel5.target, graphical.target
          • 6 - runlevel6.target, reboot.target
          • emergency - emergency.target
  • with init/telinit you can tell what level to run

• systemctl

  • How you drive/control systemd
  • How you start, stop, restart applications (just like kubectl)
  • E.g.
    • Status sound card : sudo systemctl status sound.target
    • stop sound card : sudo systemctl stop sound.target
    • Status sound card : sudo systemctl status sound.target
    • start sound card : sudo systemctl start sound.target
    • Status sound card : sudo systemctl status sound.target

• Commands

  • ps : List active processes
  • ps aux | head : Shows the top processes where you will seee /sbin/init
  • dmesg : Kernel messages logged from the last bootup
  • head : take first n lines
  • tail : take last n lines
  • less : page through a long result
  • man : manual
  • sudo wall : Send a message to anyone logged in/has open shell (like announce a reboot)
  • which : Where is an app running from?

Linux Installation and Package Management #

• Design hard disk layout

  • / : root
  • /usr : user binaries installed
  • /home :
  • /boot : All related to booting
  • /var : Variable data (e.g. system logs …)
  • /tmp : Everyone on the system can write to

• Partitions

  • Divide storage in multiple pieces
  • Allows dual booting
  • Separation of files
  • Data organization
  • System protection
  • e.g. Separate partition for each user to separate and safeguard
  • When you create a partition you need to mount them to directories.
  • Every path in linux can be mounted to
    • We can mount to :
      • /home
      • /var
      • /tmp
      • /home/nick/blah/
    • Remember like with Docker. You can have a folder /home/ian/dbdata with data in it.
      • When you mount a partition to /home/ian/dbdata, the data in there will be hidden and overtaken with this mounted partition (like a volume with docker)
      • Once you unmoun the partition from that folder, the original data is again visible and accessible.

• Swap

  • Swap is a partition, used in case the RAM is full, Swap is used
  • Unused pages fo the RAM will be saved in the SWAP partition

• LVM

  • Logical Volume Manager
  • (like Disk Manager windows, on steroids)
  • Allows to split disks into pools (Pools are also known as PE, Physical Extends)
  • Create partitions from pools
  • Can grow or shrink partitions

• Install a boot manager

  • Boot Loader

    • Boots a linux system
    • Runs before the OS
    • Can be configured from the operating system
    • common boot loaders :
      • LILO
      • GRUB Legacy
      • GRUB2

  • Configuring the /boot/grub/grub.cfg results in editing your boot loader logic

  • Although the above is the auto generated result of /etc/grub.d and /etc/default/grub using grub-mkconfig

  • grub-probe

  • grub-install : To install grub to the MBR of the specified disk (in case that didn’t happen yet)

  • Revise

    • update sudo vi /etc/default/grub file
    • run sudo update-grub
    • restart to see changes in action

• Manage Shared Libraries

  • Libraries : So typical libs/packages that bash scripts or actual code can use
  • Key properties
    • Shared
    • Reusable
  • Linking
    • When your application wants to use these libraries, they should be linked to them
      • Static Linking : Library is included in the application (each app has its own copy)
      • Dynamic Linking : Different applications using the exact same copy of the library
        • Update libraries in a single place
        • /etc/ld.so.conf lists the locations of the shared libraries on your system.
        • include statements means it was split into other linked files
    • ldd : ldd prints the shared objects (shared libraries) required by each program or shared object specified on the command line.
      • e.g. ldd /bin/ls

• Use debian package manager

  • dpkg : Debian Package Manager
    • install/upgrade/remove software
    • low level tool
    • (Does not automatically installes dependencies)
  • apt
    • Advanced packaging tool
    • high level tool
    • install/upgrade/remove software
    • handles upgrading of entire system
    • Handle all package dependencies automatically
    • Uses online repositories
  • /etc/apt/sources.list is the list for mirrors of apt and specifics on which repos per mirror to use
    • main : Officially supported software
    • restricted : supported software (not free under completely free license)
    • xenial : current version
    • universe : community maintained software
    • multiverse : Not free software
  • apt-get update : update local package lists
  • apt-get install <name> : Install software
  • apt-get remove <name> : Uninstall software
    • ! does not remove remaining config files, use dpkg --purge <name> for cleanup
  • apt-cache depends <name> : Show what a app depends on
  • apt-cache search <name> : Search for packages with a particular name
  • apt-get upgrade : Upgrade all current installed packages (respecting semver)
  • apt-get dist-upgrade : upgrade everything and remove anything unused

• wget Download a file to current location

• Use RPM and YUM package manager

  • RPM
    • RedHat Package Manager
    • rpm command
    • Low level tools
    • install/upgrade/remove software
  • YUM
    • Yellowdog update/modifier
    • replaced YUP (yellowdog updater)
    • Utilites online repositories
    • manages dependencies

• Quiz

  • How do you temporarily add a directory to your shared library path? - LD_LIBRARY_PATH

GNU and Unix Commands #

Devices, filesystems and filesystem hierarchy #

Shells, scripting and data management #

User Interface and Desktop #

Manage user and group accounts and related system files #

Essential System Services #

Networking fundamentals #

Security #