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

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

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