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https://github.com/PrivSec-dev/privsec.dev
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344 lines
11 KiB
Markdown
344 lines
11 KiB
Markdown
---
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title: "Root ZFS Encryption, Mirroring, and Remote Unlocking on Ubuntu"
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tags: ['Operating Systems', 'Linux', 'Security']
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date: 2023-07-26
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author: Tommy
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---
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While Unbutu supports ZFS on root filesystems with an easy snapshot and rollback mechanism called ZSYS, ZSYS is [soon going to be deprecated](https://bugs.launchpad.net/ubuntu/+source/ubiquity/+bug/1966773) and the installer does not offer an easy way to setup mirroring. In this guide, I will walk you through how to set up Ubuntu with root on ZFS, mirroring with both the root and EFI partitions, and remote unlocking + boot into a snapshot with ZFSBootMenu.
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## Enter the Shell
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Enter the shell on your Ubuntu Installer:
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## Partitioning the Disk
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Esentially, we need a 512MB ESP partition for ZFSBootMenu and a `/` partition for the rest of the system. If you are using a single disk, just make those 2 partitions on your disk. If you are planning to do mirroring, set up both on of these partitions on each disk.
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There are a variety of tools you can use, but an easy to use one would be `cfdisk`.
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```bash
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cfdisk /dev/nvme0n1
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cfdisk /dev/nvme0n2
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```
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## Mirroring the ESP partition
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_Skip this if you are not doing mirroring_
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While the EFI specs do not support `mdadm`, we can setup mdadm with metadata v1.0, which will be put at the end of the parition and allows it to boot.
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```bash
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mdadm --create /dev/md0 --level 1 --raid-disks --metadata 1.0 /dev/nvme0n1p1 /dev/nvme0n1p2
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mkfs.fat -F 32 /dev/md0
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```
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## Setup the ZFS partition
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This part is mostly based on the [official ZFSBootMenu guide](https://docs.zfsbootmenu.org/en/v2.2.x/guides/ubuntu/uefi.html) with some changes to work around some not-so-great instructions there.
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### Creating the zpool
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#### Getting the Disk ID.
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First, we must get the disk IDs from `/dev/disk/by-id`. The official guide uses the dynamically assigned drive identifier (`/dev/sda`, `/dev/nvme0n1`, etc), which is not what we want to do with zpools, since it will cause problems later on.
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#### Installing ZFS-Utils
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```bash
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sudo apt install zfsutils-linux -y
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```
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#### Create the encryption key
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```bash
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echo 'SomeKeyphrase' > /etc/zfs/zroot.key
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chmod 000 /etc/zfs/zroot.key
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```
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#### For Non-Mirrored Setups
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```bash
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sudo zpool create -o ashift=12 -O compression=zstd -O acltype=posixacl -O xattr=sa -O atime=off -O encryption=on -O keylocation=file:///etc/zfs/zroot.key -O keyformat=passphrase -o autotrim=on -o failmode=panic compatibility=openzfs-2.1-linux -m none zroot /dev/disk/by-id/nvme-SAMSUNG_MZQL21T9HCJR-00A07_XXXXXXX-part2
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```
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#### For Mirrored Setups
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```bash
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zpool create -o ashift=12 -O compression=zstd -O acltype=posixacl -O xattr=sa -O atime=off -O encryption=on -O keylocation=file:///etc/zfs/zroot.key -O keyformat=passphrase -o autotrim=on -o failmode=panic compatibility=openzfs-2.1-linux -m none zroot mirror /dev/disk/by-id/nvme-SAMSUNG_MZQL21T9HCJR-00A07_XXXXXXX-part2 /dev/disk/by-id/nvme-SAMSUNG_MZQL21T9HCJR-00A07_YYYYYYY-part2
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```
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#### Notes
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We use slightly different options than the official guide. Most notably, `atime` is disabled as it has detrimental effect on performance and unnecessarily increases write operations. `compression` is changed from `lz4` to `zstd` as it has much better compression ratio than `lz4` while still maintaining good performance. We did not specify the encryption type here as `aes-256-gcm` is already the default with openZFS >= 0.8.4. failmode=panic makes sure that the kernel panics in case there is something wrong with the drive instead of taking risks with abnormal behavior. We specify compatibility=openzfs-2.1-linux to make sure that updates will not make the system unbootable in the future.
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### Creating the filesystems
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```bash
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zfs create -o mountpoint=none zroot/ROOT
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zfs create -o mountpoint=/ -o canmount=noauto zroot/ROOT/ubuntu
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zfs create -o mountpoint=/home zroot/home
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zfs create -o mountpoint=/var/log zroot/ROOT/ubuntu/log
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zfs create -o mountpoint=/var/spool zroot/ROOT/ubuntu/spool
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zfs create -o mountpoint=/var/cache zroot/ROOT/ubuntu/cache
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zpool set bootfs=zroot/ROOT/ubuntu zroot
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```
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Here, we deviate from the official guide by splitting out `/var/log`, `/var/spool`, `/var/cache` out into their own datasets. These are directories which are parts of Ubuntu that we do not want to be rolled back along with the system in case we need to boot into a prior snapshot.
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### Mounting the filesystem
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```bash
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zpool export zroot
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zpool import -N -R /mnt zroot
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zfs load-key -L prompt zroot
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zfs mount zroot/ROOT/ubuntu
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zfs mount zroot/ROOT/ubuntu/log
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zfs mount zroot/ROOT/ubuntu/cache
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zfs mount zroot/ROOT/ubuntu/spool
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zfs mount zroot/home
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```
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### Update device symlink
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```bash
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udevadm trigger
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```
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## Install Ubuntu
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We will deviate from the ZFSBootMenu's documentation here, as it only installs a minimal system with SysVinit. Instead, we can install ubuntu-server-minimal.
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### Bootstrapping
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```bash
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zgenhostid -f 0x00bab10c
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apt install -y debootstrap
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debootstrap jammy /mnt
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```
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### Copy files into the new install
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```bash
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cp /etc/hostid /mnt/etc/hostid
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cp /etc/resolv.conf /mnt/etc/
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mkdir /mnt/etc/zfs
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cp /etc/zfs/zroot.key /mnt/etc/zfs
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```
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### Chroot into the new OS
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```bash
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mount -t proc proc /mnt/proc
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mount -t sysfs sys /mnt/sys
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mount -B /dev /mnt/dev
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mount -t devpts pts /mnt/dev/pts
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chroot /mnt /bin/bash
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```
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### Setup the repositories
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Use the source list from the Ubuntu live ISO:
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```bash
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cat <<EOF > /etc/apt/sources.list
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# See http://help.ubuntu.com/community/UpgradeNotes for how to upgrade to
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# newer versions of the distribution.
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deb http://archive.ubuntu.com/ubuntu/ jammy main restricted
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# deb-src http://archive.ubuntu.com/ubuntu/ jammy main restricted
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## Major bug fix updates produced after the final release of the
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## distribution.
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deb http://archive.ubuntu.com/ubuntu/ jammy-updates main restricted
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# deb-src http://archive.ubuntu.com/ubuntu/ jammy-updates main restricted
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## N.B. software from this repository is ENTIRELY UNSUPPORTED by the Ubuntu
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## team. Also, please note that software in universe WILL NOT receive any
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## review or updates from the Ubuntu security team.
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deb http://archive.ubuntu.com/ubuntu/ jammy universe
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# deb-src http://archive.ubuntu.com/ubuntu/ jammy universe
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deb http://archive.ubuntu.com/ubuntu/ jammy-updates universe
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# deb-src http://archive.ubuntu.com/ubuntu/ jammy-updates universe
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## N.B. software from this repository is ENTIRELY UNSUPPORTED by the Ubuntu
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## team, and may not be under a free licence. Please satisfy yourself as to
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## your rights to use the software. Also, please note that software in
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## multiverse WILL NOT receive any review or updates from the Ubuntu
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## security team.
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deb http://archive.ubuntu.com/ubuntu/ jammy multiverse
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# deb-src http://archive.ubuntu.com/ubuntu/ jammy multiverse
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deb http://archive.ubuntu.com/ubuntu/ jammy-updates multiverse
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# deb-src http://archive.ubuntu.com/ubuntu/ jammy-updates multiverse
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## N.B. software from this repository may not have been tested as
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## extensively as that contained in the main release, although it includes
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## newer versions of some applications which may provide useful features.
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## Also, please note that software in backports WILL NOT receive any review
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## or updates from the Ubuntu security team.
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deb http://archive.ubuntu.com/ubuntu/ jammy-backports main restricted universe multiverse
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# deb-src http://archive.ubuntu.com/ubuntu/ jammy-backports main restricted universe multiverse
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deb http://security.ubuntu.com/ubuntu/ jammy-security main restricted
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# deb-src http://security.ubuntu.com/ubuntu/ jammy-security main restricted
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deb http://security.ubuntu.com/ubuntu/ jammy-security universe
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# deb-src http://security.ubuntu.com/ubuntu/ jammy-security universe
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deb http://security.ubuntu.com/ubuntu/ jammy-security multiverse
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# deb-src http://security.ubuntu.com/ubuntu/ jammy-security multiverse
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EOF
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```
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### Install the necessary packages
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```bash
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apt update
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apt install --no-install-recommends linux-generic ubuntu-server-minimal
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```
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### Configure packages to customize local and console properties
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```bash
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dpkg-reconfigure locales tzdata keyboard-configuration console-setup
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```
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## ZFS Configuration
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### Install required packages
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```bash
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apt install dosfstools zfs-initramfs zfsutils-linux
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```
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### Enable systemd ZFS services
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```bash
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systemctl enable zfs.target
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systemctl enable zfs-import-cache
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systemctl enable zfs-mount
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systemctl enable zfs-import.target
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```
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### Enable systemd-networkd
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```bash
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systemctl enable systemd-networkd
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```
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### Configure `initramfs-tools`
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```bash
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echo "UMASK=0077" > /etc/initramfs-tools/conf.d/umask.conf
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```
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### Rebuild the initramfs
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```bash
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update-initramfs -c -k all
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```
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## Install and configure ZFSBootMenu
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### Setup the EFI partition
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If you are doing mirroring:
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```bash
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zfs set org.zfsbootmenu:commandline="quiet loglevel=4" zroot/ROOT
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zfs set org.zfsbootmenu:keysource="zroot/ROOT/ubuntu" zroot
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cat << EOF >> /etc/fstab
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$( blkid | grep /dev/md0 | cut -d ' ' -f 2 ) /boot/efi vfat defaults 0 0
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EOF
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mkdir -p /boot/efi
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mount /boot/efi
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```
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If you are not, just replace `md0` in the commands above with your efi partition.
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### Install ZFSBootMenu
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#### To use it without remote unlocking, just follow the official guide:
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```
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apt install curl -y
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mkdir -p /boot/efi/EFI/ZBM
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curl -o /boot/efi/EFI/ZBM/VMLINUZ.EFI -L https://get.zfsbootmenu.org/efi
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cp /boot/efi/EFI/ZBM/VMLINUZ.EFI /boot/efi/EFI/ZBM/VMLINUZ-BACKUP.EFI
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```
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#### To use it with remote unlocking, you have to compile the package:
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```bash
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git clone https://github.com/dracut-crypt-ssh/dracut-crypt-ssh
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apt install -y blah blah blah dependency here I forgot
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some build command here
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echo 'omit_dracutmodules+=" crypt-ssh "' >> /etc/dracut-config-location-idk
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mkdir -p /etc/dropbear
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ssh-keygen -t rsa -m PEM -f /etc/dropbear/ssh_host_rsa_key
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ssh-keygen -t ecdsa -m PEM -f /etc/dropbear/ssh_host_ecdsa_key
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ssh-keygen -t ed25519 -m PEM -f /etc/dropbear/ssh_host_ed25519_key
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mkdir -p /etc/cmdline.d
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echo "ip=dhcp rd.neednet=1" > /etc/cmdline.d/dracut-network.conf
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cat <<EOF > /etc/zfsbootmenu/dracut.conf.d/dropbear.conf
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# Enable dropbear ssh server and pull in network configuration args
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add_dracutmodules+=" crypt-ssh "
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install_optional_items+=" /etc/cmdline.d/dracut-network.conf "
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# Copy system keys for consistent access
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dropbear_rsa_key=/etc/dropbear/ssh_host_rsa_key
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dropbear_ecdsa_key=/etc/dropbear/ssh_host_ecdsa_key
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dropbear_ed25519_key=/etc/dropbear/ssh_host_ed25519_key
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# User zbmuser is the authorized unlocker here
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dropbear_acl=/home/zbmuser/.ssh/authorized_keys
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EOF
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```
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### Configure EFI boot entries
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```bash
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mount -t efivarfs efivarfs /sys/firmware/efi/efivars
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apt install efibootmgr -y
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efibootmgr -c -d "/dev/nvme0n1" -p 1 \
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-L "ZFSBootMenu" \
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-l \\EFI\\ZBM\\VMLINUZ.EFI
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efibootmgr -c -d /dev/nvme0n1 -p 1 \
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-L "ZFSBootMenu (Backup)" \
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-l \\EFI\\ZBM\\VMLINUZ-BACKUP.EFI
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### Skip this section if you are not doing mirroring
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efibootmgr -c -d "/dev/nvme0n2" -p 1 \
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-L "ZFSBootMenu 2" \
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-l \\EFI\\ZBM\\VMLINUZ.EFI
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efibootmgr -c -d /dev/nvme0n2 -p 1 \
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-L "ZFSBootMenu 2 (Backup)" \
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-l \\EFI\\ZBM\\VMLINUZ-BACKUP.EFI
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```
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### Set the root password
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Set the root password:
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```
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passwd
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```
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### Exit the environment
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```
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exit
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umount -n -R /mnt
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zpool export zroot
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reboot
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``` |