Linux Lpic 1

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

linux_01

  • 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

linux_02

  • 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 #

Essential System Services #

Networking fundamentals #

Security #

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