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fundamentals/boot.md

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+# Basic Startup
+
+BIOS > MBR > GRUB > Kernel > Init > Run Level
+
+- The BIOS identifies system hardware.
+
+- The Master Boot Record contains partition and filesystem data.
+
+- The Grand Unified Bootloader executes the kernel.
+
+- The Init Executes designates run level (via SysVinit, Upstart, or Systemd).
+
+- Run Level starts the user's session.
+
+The Master Boot Record is a 512 byte file called boot.img which starts the first sectore of core.img into memory (GRUB Stage 1.5), which then executes /boot/grub.
+
+# Access system
+
+Ctrl+c at boot then add in
+
+> rw init=bash
+
+# Run Levels
+
+	0: Half
+	1: Single user mode
+	2: Multi-user, without NFS
+	3: Full multi-user mode
+	4: Unused
+	5: X11
+	6: Reboot
+
+None of this is used by humans anymore - it's all systemd.
+
+# Systemd
+
+See what's running with ....
+
+> systemctl list-units
+
+Stop, start, whatever with:
+
+systemctl enable|stop|start httpd
+
+This starts httpd (Fedora's word for Apache2).
+
+# Boot Records
+
+'File System Tab' under /etc/fstab keeps track of the partitions and boot order.
+
+The logical voluem manager (LVM) can make non-hardware partitions.
+
+The nomenclature is:
+
+- PV = physical volume
+
+- LV = logical volume
+
+- VG = volume group
+
+# Volume Groups
+
+> sudo vgcreate work-volume /dev/sdb2 /dev/sdb4
+
+This creates the volume group 'work-volume', consisting in sdb2 and sdb4.
+
+Now you ahve a volume group, you can use it as part of a new logical volume.
+
+> sudo lvcreate -n noob-lv work-volume
+
+Then scan for all logical volumes on the system with lvscan.
+
+> sudo lvscan
+
+# GRUB
+
+Install a grub with either:
+
+> sudo grub-install /dev/sda
+
+or
+
+> sudo grub2-install /dev/sda
+
+This takes all settings from /etc/fstab.
+
+Then when done editing settings update the script in /boot/grub/grub.cfg (in Debian) or /boot/boot/grub/menu (in other systems).
+
+There are default examples in /etc/grub.d/ (but not on Ubuntu).
+
+Finalize your settings with grub-mkconfig (or grub2-mkconfig), or update-grub.
+
+# Cowardice
+
+If you can't do that, use boot-repair:
+
+> help.ubuntu.com/community/Boot-Repair
+