Linux boot process.ipynb

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    "# Boot Process\n",
    "\n",
    "\n",
    "Bios -> POST -> Sector 0 of bootable device -> Boot loader -> Kernel & Initrd (initramfs) -> Kernel -> Init\n",
    "\n",
    "- Bios\n",
    "    - Basic input output\n",
    "    - Is a frimware stored on R/O chip\n",
    "    - First program that runs when sys powers on\n",
    "    - Performs POST\n",
    "    - Locate and runs boot loader\n",
    "    - Provides an interface to configure hardware\n",
    "        - Active onboard HW\n",
    "        - Boot order, etc.\n",
    "    - non-volatile\n",
    "    \n",
    "\n",
    "- CMOS\n",
    "    - Is a special memory chip\n",
    "    - Hold basic informations (256 Byte)\n",
    "     - Current date and time\n",
    "     - HW configuration needed by BIOS\n",
    "         - Boot sequence\n",
    "     - volatile (Battery)\n",
    "     - Complementary metal oxide semiconductor\n",
    "     \n",
    "\n",
    "- Post\n",
    "    - Power on self-test  \n",
    "    - Does moderboard works?\n",
    "    - Is GPU installed?\n",
    "    - Is memory working correctly?\n",
    "    \n",
    "    \n",
    "- MBR\n",
    "    - Master Boot Record (512 Byte)\n",
    "    - The first sector of the computer hard drive [sector 0]\n",
    "    - Magic Code [2 Byte] (0xAA55) (0b1010101001010101)\n",
    "        - BIOS will try booting the system\n",
    "        - Garbled or 0x0000 [error/tries booting the next disk]\n",
    "    - How the hard drive is partitioned [Partition table] (64 Byte)\n",
    "    - How to load the operating system [Boot Code / Bootloader] (446 Byte)\n",
    "    \n",
    "## MBR layout\n",
    "\n",
    "<img src=\"img/mbr.png\">\n",
    "\n",
    "## Bootloaders [N05]\n",
    "\n",
    "- Lilo\n",
    "    - Does not understand or parse filesystem\n",
    "    - /etc/lilo.conf\n",
    "    - information about location of kernel and ram disks, the configuration file is written with bootloader code into MBR\n",
    "    \n",
    "    \n",
    "- Grub legacy\n",
    "    - Logic to read common file systems\n",
    "    - 3 Stages\n",
    "\n",
    "\n",
    "- Grub2\n",
    "    - automatically generated\n",
    "    - chain-loading\n",
    "    - full scripting language: variables, conditionals, and loops are available\n",
    "    - available for several other types of system\n",
    "    - can read files directly from LVM and RAID\n",
    "    - [Changes from legacy](https://www.gnu.org/software/grub/manual/grub.html#Changes-from-GRUB-Legacy) \n",
    " \n",
    " \n",
    "- Syslinux\n",
    "    - Specializes in booting full Linux installations from FAT filesystems\n",
    "    - Live USBs\n",
    "    - Linux live CDs and bootable install CDs\n",
    "\n",
    "#### Initrd or Initramfs [N01.1]\n",
    "\n",
    "# Init\n",
    "\n",
    "- Process N1\n",
    "    - Runlevels\n",
    "        - Daemons (services)\n",
    "        - Desktop login manager (if any)\n",
    "        - All other programs\n",
    "\n",
    "\n",
    "  \n",
    "  \n",
    "- init systems\n",
    "    - BSD-Style\n",
    "    - SysV\n",
    "    - Upstart\n",
    "    - openrc\n",
    "    - systemd\n",
    "    - shepherd\n",
    "\n",
    "\n",
    "How knows where these stuff are? [N20]"
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    "#### References\n",
    "\n",
    "https://en.wikipedia.org/wiki/Linux_startup_process  \n",
    "http://www.wisegeek.org/what-is-cmos.htm  \n",
    "http://www.computerhope.com/issues/ch001360.htm  \n",
    "https://www.howtogeek.com/180798/where-is-the-bios-stored/  \n",
    "https://en.wikipedia.org/wiki/Nonvolatile_BIOS_memory"
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    "- - -\n",
    "## Lecture notes\n",
    "\n",
    "- All lecture notes are available at github in `ipynb` format: [https://github.com/ravexina/linux-notes](https://github.com/ravexina/linux-notes). \n",
    "\n",
    "\n",
    "- There are `html` exports of project available at: [https://ravexina.github.io/linux-notes](https://ravexina.github.io/linux-notes).\n",
    "- - -\n",
    "\n",
    "## License\n",
    "<a rel=\"license\" href=\"http://creativecommons.org/licenses/by-nc-sa/4.0/\">\n",
    "<img alt=\"Creative Commons License\" style=\"border-width:0\" src=\"https://i.creativecommons.org/l/by-nc-sa/4.0/88x31.png\" />\n",
    "</a>\n",
    "\n",
    "<span property=\"dct:title\">Linux Notes</span> by \n",
    "<a href=\"http://github.com/ravexina/Linux-Notes\" property=\"cc:attributionName\" rel=\"cc:attributionURL\">Milad As (Ravexina)</a> is licensed under a <a rel=\"license\" href=\"http://creativecommons.org/licenses/by-nc-sa/4.0/\">Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License</a>.\n",
    "\n",
    "- - -\n",
    "\n",
    "<a rel=\"license\" href=\"https://gitlab.com/ravexina/\"><img alt=\"ravexina's gitlab\" style=\"display:inline;border-width:0;height:30px;float:left;\" src=\"img/logo/logo-square.png\" /></a> \n",
    "\n",
    "<a rel=\"license\" href=\"https://github.com/ravexina/\"><img alt=\"ravexina's github\" style=\"float:right;display:inline;border-width:0;height:30px;\" src=\"img/logo/GitHub_Logo.png\" /></a>"
   ]
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