# Pre-OS prep

Review the [hardware](https://github.com/rpdelaney/iris-setup/blob/master/HARDWARE.md).

We're putting the O/S on the NVME disk, `/dev/nvme0n1`.

```
+---------------------------+-----------------------------------------------+
| Boot loader               | LVM volume            | LVM volume            |
| mountpoint: /boot         | mountpoint: swap      | mountpoint: /         |
|                           | /dev/volgroup0/swap   | /dev/volgroup0/root   |
|                           |_ _ _ _ _ _ _ _ _ _ _ _|_ _ _ _ _ _ _ _ _ _ _ _|
|                           |                                               |
| LUKS2 encrypted partition |              LUKS2 encrypted partition        |
| /dev/nvme0n1p1            |                /dev/nvme0n1p2                 |
+---------------------------+-----------------------------------------------+
```

## Installation media

1. [ ] Prepare the installation media: keyboard layout, system clock, and optimize the mirrorlist.

```
# loadkeys dvorak
# timedatectl set-ntp true
# pacman -Sy reflector
# cp /etc/pacman.d/mirrorlist /etc/pacman.d/mirrorlist.bak
# reflector --verbose --age 12 --sort rate --sort score --save /etc/pacman.d/mirrorlist
```

_(No dm-crypt [drive preparation](https://wiki.archlinux.org/index.php/Dm-crypt/Drive_preparation) since the disk is blank and factory-new._

## Create partitions

1. [ ] Create MBR partition tables: [GPT](https://wiki.archlinux.org/index.php/GPT)

```
# gdisk /dev/nvme0n1
```

Device         | Type Hex Code | Role      | First sector | Last sector
---------------|---------------| ----------|--------------|------------
/dev/nvme0n1p1 | EF02          | BIOS boot | 2048         | +1M
/dev/nvme0n1p2 | 8300          | Linux FS  | default      | default

## Create LUKS container

1. [ ] Format the LUKS container:

```
# cryptsetup luksFormat --type luks1 --use-random --hash whirlpool --iter-time 5000 /dev/nvme0n1p2
```

1. [ ] [Backup LUKS headers](https://wiki.archlinux.org/index.php/Dm-crypt/Device_encryption#Backup_and_restore)

## O/S Filesystem

Decrypt and mount the encrypted root partition.

```
# cryptsetup open --allow-discards --type luks1 /dev/nvme0n1p2 cryptlvm
```

### Create and mount LVM volumes

_Main article: [LVM](https://wiki.archlinux.org/index.php/LVM#Create_file_systems_and_mount_logical_volumes)_

1. [ ] Create LVM group and volumes for root and swap.

```
# vgcreate volgroup0 /dev/mapper/cryptlvm
# lvcreate volgroup0 -L 32G -n lvswap
# lvcreate volgroup0 -l 100%FREE -n lvroot
```

* To display created volume groups, `vgdisplay`
* To display created logical volumes, `lvdisplay`

### Create btrfs filesystem

1. [ ] Format the root LVM volume and create the swap:

```
# mkfs.btrfs -L root /dev/volgroup0/lvroot
# mkswap -L swap /dev/volgroup0/lvswap
# swapon -L swap
```

Now we will create the following subvolumes:

```
subvolid=5 (/dev/volgroup0/lvroot)
   └──| @ (mounted as /)
      ├── /home
      ├── /var/abs
      ├── /var/tmp
      └── /var/cache/pacman/pkg
```

We will create a subvolume for snapshots later, when setting up snapper.

Mount the newly created filesystem with zstd compression.

```
# mount -o compress=zstd /dev/volgroup0/lvroot /mnt
```

1. [ ] Now, create the top-level subvolume:

```
# btrfs subvolume create /mnt/@
# umount /mnt
```

Next mount the top-level subvolume:

```
# mount -o compress=zstd,subvol=@ /dev/volgroup0/lvroot /mnt
```

1. [ ] Create nested subvolumes that we do **not** want to have in the snapshot when taking snapshots of `/`.

```
# btrfs subvolume create /mnt/home
# mkdir -p /mnt/var
# btrfs subvolume create /mnt/var/abs
# btrfs subvolume create /mnt/var/tmp
# mkdir -p /mnt/var/cache/pacman
# btrfs subvolume create /mnt/var/cache/pacman/pkg
```

Mount the nested subvolumes:

```
# mount -o compress=zstd,subvol=@/var/abs /dev/volgroup0/lvroot /mnt/var/abs
# mount -o compress=zstd,subvol=@/var/tmp /dev/volgroup0/lvroot /mnt/var/tmp
# mount -o compress=zstd,subvol=@/var/cache/pacman/pkg /dev/volgroup0/lvroot /mnt/var/cache/pacman/pkg
```

* To see a list of current subvolumes: `btrfs subvolume list -a /mnt`
* To delete a subvolume: `btrfs subvolume delete /path/to/subvolume`

## O/S

_Continue to [OS Installation Plan](https://github.com/rpdelaney/iris-setup/blob/master/BOOTSTRAP.md)_

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