Merge pull request '26-install-zfs-only-when-needed' (#27) from 26-install-zfs-only-when-needed into main

Reviewed-on: #27

.gitignore

@@ -0,0 +1,2 @@
+archzbm_settings.env
+.idea

README.md

@@ -82,7 +82,7 @@ NAME         SIZE FSTYPE PARTTYPE PARTTYPENAME PTTYPE
 
 # Partition naming
 
-Since this script works with UEFI and legacy BIOS mode we'll be addressing both disk layout schemes with umbrella terms for better readability: "The zpool partition" will be GPT `BF00` partition and MBR `bf` partition. You'll parse the text accordingly. "The boot partition" will be GPT `EF00` partition as well as the MBR `83` partition.
+Since this script works with UEFI and legacy BIOS mode we'll be addressing both disk layout schemes with umbrella terms for the rest of this document for better readability: "The zpool partition" will be GPT `BF00` partition and MBR `bf` partition. You'll parse the text accordingly. "The boot partition" will be GPT `EF00` partition as well as the MBR `83` partition.
 
 # ZFS dataset layout
 
@@ -99,6 +99,40 @@ The script will create a single ZFS zpool `zpool` on the zpool partition with da
 
 ## Options
 
+The following options can be given either by exporting them as shell variables prior to script execution or in a file named `archzbm_settings.env` that lives in your current working directory where you're about to execute the script. You can walk yourself through an interactive questionnaire that helps create a valid `archzbm_settings.env` file. Check out [Command line setup help](#command-line-setup-help) for details on the questionnaire.
+
+If you instead want to define settings yourself with an `archzbm_settings.env` file its file format is identical to shell variable assignments of the form `VAR=value` or `VAR='value'`.
+
+If `./archzbm_settings.env` exists the script will `source` its content and `export` all variables for use in future steps.
+
+In cases where a variable is both exported prior to script execution and specified in `archzbm_settings.env` the latter will override the former.
+
+Known options are as follows.
+
+### Kernel downgrade
+
+By default we install newest `linux` and `linux-headers` packages into a `chroot`. Once we're in that `chroot` we then install newest [AUR zfs-dkms package](https://aur.archlinux.org/packages/zfs-dkms). You may want to override `linux` and `linux-headers` versions to ensure you end up with a compatible mix between them and `zfs-dkms`.
+
+For example:
+```
+export ARCHZBM_KERNEL_VER=6.5.9.arch2
+```
+
+In our `chroot` this will trigger execution of:
+```
+downgrade --ala-only 'linux=6.5.9.arch2' 'linux-headers=6.5.9.arch2' --ignore always
+```
+
+Where `downgrade` is the [AUR downgrade package](https://aur.archlinux.org/packages/downgrade). This will downgrade `linux` and `linux-headers` and will add a setting to your `/etc/pacman.conf`:
+```
+[options]
+IgnorePkg = linux linux-headers
+```
+
+Setting `ARCHZBM_KERNEL_VER` to an empty string `''` or keeping it undefined are both valid and will retain newest versions instead of downgrading.
+
+Also read [Kernel selection](#kernel-selection) for details.
+
 ### Compression
 
 By default we create a zpool with ZFS property `compression=on`. If the `lz4_compress` pool feature is active this will by default enable `compression=lz4`. See `man 7 zfsprops` for example in ZFS 2.1.9 for details. See `zpool get feature@lz4_compress <pool>` to check this feature's status on your `<pool>`.
@@ -117,12 +151,143 @@ To get a zpool with unencrypted datasets export the shell variable `ARCHZBM_ZFSP
 export ARCHZBM_ZFSPROPS_NO_ENCRYPTION=yup
 ```
 
+### Passwords
+
+By default both the zpool password and the account password for `root` are literally `password`. While you can certainly change these after initial system setup (see [Password change](#password-change)) you can also optionally set passwords before script execution as follows:
+
+```
+ARCHZBM_ZPOOL_PASSWORD='a fancy password'
+ARCHZBM_ROOT_PASSWORD='t0psecr3t!'
+```
+
+> While the `root` password is allowed to be weak and `chpasswd` won't care do make sure to set a zpool password that meets ZFS' complexity rules. Per `man 7 zfsprops` section `keyformat` the only requirement is a length "between 8 and 512 bytes" (as in minimum 8 characters). If you pick a password that's too weak ZFS will reject zpool creation and very ungracefully derail the rest of this script. The script doesn't check what you're setting.
+
+The script does create a second user named `build` but doesn't set a password on account creation. It's intended as a helper for system setup tasks such as `sudo -u build paru -S <package>` where an account password is irrelevant since `root` can always `sudo` whatever it wants. You will not be able to log in to the `build` account yourself although you certainly could set a password for it. Instead we suggest you create a proper user account for yourself. Your newly installed Arch Linux comes with an `/etc/motd` greeting that summarizes this as:
+
+```
+useradd --create-home --shell /bin/bash --user-group --groups wheel <user>
+passwd <user>
+```
+
+### Networking
+
+By default the script configures plain ZFSBootMenu without networking nor an SSH server. If you're interested in SSH-ing into your ZFSBootMenu boot loader you're going to want to specify some of the following variables.
+
+#### IP address
+
+> IPv6 addresses are untested. Script has been confirmed working with IPv4 addresses.
+
+```
+ARCHZBM_NET_CLIENT_IP=''
+ARCHZBM_NET_SERVER_IP=''
+ARCHZBM_NET_GATEWAY_IP=''
+ARCHZBM_NET_NETMASK=''
+ARCHZBM_NET_HOSTNAME=''
+ARCHZBM_NET_DEVICE=''
+ARCHZBM_NET_AUTOCONF=''
+```
+
+By default none of the variables are set to any value and no networking will be available in ZFSBootMenu. If you want networking as in an IP address bound to a network interface set at least one of these variables or one of the [SSH](#ssh) variables listed further down. Setting one or more `ARCHZBM_NET_*` variables to an empty string is valid. If at least one variable is given either from this paragraph or from [SSH](#ssh) we're assuming that you want networking. Unspecified values and values set to the empty string `''` use defaults.
+
+For networking we rely on the [mkinitcpio-nfs-utils](https://archlinux.org/packages/core/x86_64/mkinitcpio-nfs-utils/) package with its `net` hook. Please refer to its [initcpio-install-net](https://gitlab.archlinux.org/archlinux/packaging/packages/mkinitcpio-nfs-utils/-/blob/main/initcpio-install-net) script file for usage hints on above variables. The hook implements a subset of the [ip Kernel Command Line argument](https://docs.kernel.org/admin-guide/nfs/nfsroot.html).
+
+Mapping between `net` hook field names and our shell variables is straightforward. Fields 8, 9 and 10 (DNS and NTP server addresses) from the official `ip` docs are unsupported in `net` hook. As such our hook has a total of 7 fields available for you to configure.
+
+```
++-------------+------------------------+
+|  net hook   |       This script      |
++-------------+------------------------+
+| <client-ip> | ARCHZBM_NET_CLIENT_IP  |
+| <server-ip> | ARCHZBM_NET_SERVER_IP  |
+| <gw-ip>     | ARCHZBM_NET_GATEWAY_IP |
+| <netmask>   | ARCHZBM_NET_NETMASK    |
+| <hostname>  | ARCHZBM_NET_HOSTNAME   |
+| <device>    | ARCHZBM_NET_DEVICE     |
+| <autoconf>  | ARCHZBM_NET_AUTOCONF   |
++-------------+------------------------+
+```
+
+A valid example with a few fields populated may look like so:
+
+```
+ARCHZBM_NET_CLIENT_IP='10.10.10.2'
+ARCHZBM_NET_GATEWAY_IP='10.10.10.1'
+ARCHZBM_NET_NETMASK='255.255.255.0'
+ARCHZBM_NET_DEVICE='eth0'
+ARCHZBM_NET_AUTOCONF='none'
+```
+
+Note that in this example `ARCHZBM_NET_SERVER_IP` and `ARCHZBM_NET_HOSTNAME` are left unassigned.
+
+It'll add the following `ip=` instruction to your Kernel Command Line:
+```
+ip=10.10.10.2::10.10.10.1:255.255.255.0::eth0:none
+```
+
+This is also valid and will configure `eth0` via DHCP:
+
+```
+ARCHZBM_NET_DEVICE='eth0'
+ARCHZBM_NET_AUTOCONF='dhcp'
+```
+
+> In ZFSBootMenu the device names that go into `ARCHZBM_NET_DEVICE` are raw unchanged kernel device names such as `eth0`. If you're unsure which device name to use in your Arch Linux live CD ISO image check `dmesg` output. During boot typically a kernel module will first assign the raw kernel device name then later `systemd` will enforce [Predictable Network Interface Names](https://www.freedesktop.org/wiki/Software/systemd/PredictableNetworkInterfaceNames/).
+>
+> In `dmesg | grep` on a physical PC with an MSI B550-A Pro mainboard from 2020 that comes with one onboard Realtek RTL8111H network adapter governed by the Realtek RTL-8169 Gigabit Ethernet driver from the `r8169` kernel module you will for example see:
+> ```
+> # dmesg -T | grep eth
+> [time] r8169 0000:2a:00.0 eth0: RTL8168h/8111h, 04:7c:16:00:01:02, XID 541, IRQ 95
+> [time] r8169 0000:2a:00.0 eth0: jumbo features [frames: 9194 bytes, tx checksumming: ko]
+> [time] r8169 0000:2a:00.0 enp42s0: renamed from eth0
+> ```
+>
+> Notice how a Predictable Network Interface Name comes in on line 3. What *__you__* need here is the `eth0` part.
+
+#### SSH
+
+If you want networking indicated by the fact that at least one of the `ARCHZBM_NET_*` variables is set or one of the `ARCHZBM_SSH_*` vars we assume that you want an SSH daemon as well. This comes in the form of a `dropbear` daemon with minimal configurability. Use the following variables to define Dropbear's behavior.
+
+```
+ARCHZBM_SSH_PORT='22'
+ARCHZBM_SSH_KEEPALIVE_INTVL='1'
+ARCHZBM_SSH_AUTH_KEYS=''
+```
+
+In `ARCHZBM_SSH_PORT` you specify Dropbear's listening port, this defaults to `22` if unconfigured or set to an empty string. With `ARCHZBM_SSH_KEEPALIVE_INTVL` you define at which interval Dropbear will send keepalive messages to an SSH client through the SSH connection. This defaults to `1` as in every `1` second a keepalive message is sent. Per [man 8 dropbear](https://man.archlinux.org/man/extra/dropbear/dropbear.8.en) a value of `0` disables Dropbear sending keepalive messages. We suggest to leave this on and to keep the interval short, see [SSH in ZFSBootMenu](#ssh-in-zfsbootmenu) for how to work with this.
+
+Dropbear in this setup only supports key-based authentication, no password-based authentication. The value from `ARCHZBM_SSH_AUTH_KEYS` will be converted to a list of public SSH keys allowed to SSH into Dropbear as its default `root` user while ZFSBootMenu is running. The format of `ARCHZBM_SSH_AUTH_KEYS` is a single line where `authorized_keys` entries are split with double-commas:
+
+```
+ssh-rsa Eahajei8,,ssh-ed25519 kaeD0mas ...
+```
+
+This syntax crutch allows you to use the full range of Dropbear-supported `authorized_keys` stanzas, see [man 8 dropbear](https://man.archlinux.org/man/extra/dropbear/dropbear.8.en) for what's available. Whether or not this is useful to you is another topic :) At least the functionality for stanzas is there by separating values in `ARCHZBM_SSH_AUTH_KEYS` with double-commas.
+
+## Command line setup help
+
+An interactive questionnaire can guide you through settings and goes like this:
+
+![Command line setup questionnaire](https://i.imgur.com/OXG75GH.gif)
+
+To do the questionnaire yourself start this script with the `setup` argument:
+
+```
+export SCRIPT_URL='https://quico.space/quico-os-setup/arch-zbm/raw/branch/main/setup.sh' && curl -s "${SCRIPT_URL}" | bash -s -- setup
+```
+
+When done rerun it without that argument:
+
+```
+export SCRIPT_URL='https://quico.space/quico-os-setup/arch-zbm/raw/branch/main/setup.sh' && curl -s "${SCRIPT_URL}" | bash
+```
+
 # Steps
 
 The script takes the following installation steps.
 
 1. Install ZFS tools and kernel module with [github.com/eoli3n/archiso-zfs](https://github.com/eoli3n/archiso-zfs)
 1. Create one ZFS zpool on top of zpool partition, encrypted and compressed datasets, password `password`
+    1. _See paragraph [Passwords](#passwords) to predefine your own passwords in a settings file_
     1. _See paragraphs [Compression](#compression)/[Encryption](#encryption) to optionally disable properties_
 1. Create dataset for Arch Linux and `/home`
 1. Install Arch Linux into pool
@@ -130,11 +295,49 @@ The script takes the following installation steps.
 1. Configure boot method
     - Either an EFI image with EFI boot order entries on a UEFI machine
     - Or Syslinux with `extlinux` for a legacy BIOS computer
+1. If requested by user enable SSH in ZFSBootMenu. We then also add:
+    - [quico.space/quico-os-setup/mkinitcpio-dropbear-pacman-hook](https://quico.space/quico-os-setup/mkinitcpio-dropbear-pacman-hook)
 1. Add `pacman` hooks to keep ZFSBootMenu images (and `extlinux`) updated
     - [quico.space/quico-os-setup/zbm-regen-pacman-hook](https://quico.space/quico-os-setup/zbm-regen-pacman-hook)
     - [quico.space/quico-os-setup/zbm-syslinux-pacman-hook](https://quico.space/quico-os-setup/zbm-syslinux-pacman-hook)
 1. Exit into Arch Linux live CD ISO image shell for you to `reboot` and frolick
 
+# SSH in ZFSBootMenu
+
+Per [SSH](#ssh) and [Networking](#networking) this script will optionally add a Dropbear SSH daemon to ZFSBootMenu. While the mechanism of SSH-ing into a server isn't particularly noteworthy we humbly suggest that in this particular use case you let your SSH client listen for keepalive messages from the server.
+
+```
+ssh -o ServerAliveInterval=3 -o ServerAliveCountMax=0 root@<addr> -p <port>
+```
+
+A typical workflow with Dropbear is for you to SSH into it, issue `zfs` or `zfsbootmenu` commands and allow the Arch Linux boot process to commence. As soon as you're done Dropbear will terminate as ZFSBootMenu hands control off to your operating system's kernel. Without your client listening to keepalive messages it may not realize that the connection's gone for quite some time until you harshly interrupt it.
+
+The server defaults to sending keepalive messages to your client every second.
+
+With `-o ServerAliveInterval=3` you instruct your client to send an are-your-still-there message to the server if your client ever stops getting keepalive messages from the server for 3 seconds. The server defaults to sending 1 keepalive ping per second so even on a somewhat lossy connection we can reasonably expect to get one message through to us within 3 seconds.
+
+When it comes to the point that your SSH client sends an are-your-still-there message it expects a near-realtime response. It will accept `-o ServerAliveCountMax=0` failures from the server to comply.
+
+This effectively configures your SSH client to remain connected even through somewhat lossy hops to the Dropbear daemon; and to cleanly disconnect 3 seconds and some change after you've executed whatever you needed to do in ZFSBootMenu.
+
+# Kernel selection
+
+This script compiles ZFS via Arch Linux' [Dynamic Kernel Module Support](https://wiki.archlinux.org/title/Dynamic_Kernel_Module_Support) (DKMS). Not all kernels allow for successful compilation, in some instances a particularly recent kernel version may change APIs to such a degree that ZFS compilation simply fails.
+
+We strongly suggest to that you:
+
+- Firstly, refer to a resource such as the [Arch Linux Archive package version list](https://archive.archlinux.org/packages/l/linux/) to find out what newest kernel version this script will install.
+- Secondly, research if newest [AUR zfs-dkms package](https://aur.archlinux.org/packages/zfs-dkms) is compatible with that kernel. Two reasonable points of contact are AUR and its comments section for `zfs-dkms` where users quickly report issues; and the [github.com/openzfs/zfs issues list](https://github.com/openzfs/zfs/issues).
+
+An example for this is that `linux-6.6.1.arch1-1-x86_64` came out on Wednesday, November 8, 2023 at a time when newest `zfs-dkms` package version [was 2.2.0](https://aur.archlinux.org/cgit/aur.git/commit/?h=zfs-dkms&id=da1b6372c57b16f2781a7fda2b95971bb392c5ee) which did not compile against `linux` 6.6.x.
+
+You'd then set for example:
+```
+export ARCHZBM_KERNEL_VER=6.5.9.arch2
+```
+
+Where any 6.5.x version is known to work well with `zfs-dkms`. See also [Kernel downgrade](#kernel-downgrade) for details on how to configure this.
+
 # Flavor choices
 
 We make the following opinionated flavor choices. Feel free to change them to your liking.
@@ -152,14 +355,14 @@ We make the following opinionated flavor choices. Feel free to change them to yo
 After installation you're going to want to at least touch these points in your new Arch Linux install:
 
 - Package manager hook: `pacman` does not have a hook to do ZFS snapshots
-    - See [this GitHub gist](https://gist.github.com/Soulsuke/6a7d1f09f7fef968a2f32e0ff32a5c4c#file-arch_on_zfs-txt-L238) and [zfs-snapshotter.bash](https://github.com/Soulsuke/arch-zfs-tools/blob/master/zfs-snapshotter.bash) for inspiration
+    - See [quico.space/quico-os-setup/zfs-pacman-hook](https://quico.space/quico-os-setup/zfs-pacman-hook/src/branch/1-get-base-version-going) for an example you may want to install
 - Hostname: Installation chose a pseudo-randomly generated 8-character string with `pwgen`
     - Check `hostnamectl set-hostname <hostname>`
 - Unprivileged user accounts: The OS was installed with `root` and unprivileged `build` users
-- Passwords
+- Unless you had a settings file or exported shell env vars per [Passwords](#passwords) you're going to want to change passwords now:
     - ZFS: The password for all datasets underneath `zpool` is `password`.
     - Local `root` account: The local `root` account's password is `password`.
-- Arch User Repository (AUR) helper: We installed [paru](https://github.com/Morganamilo/paru) as our AUR helper, we installed from GitHub via `makepkg -si` then replaced itself with its [paru-bin](https://aur.archlinux.org/packages/paru-bin) version from AUR.
+- Arch User Repository (AUR) helper: We installed [paru](https://github.com/Morganamilo/paru) as our AUR helper, we installed from AUR as [paru-bin](https://aur.archlinux.org/packages/paru-bin).
 - In `/etc/systemd/network/50-wired.network` instead of a DHCP-based network config you can get a static one. The DHCP-based one for reference looks like:
     ```
     ...
@@ -193,7 +396,7 @@ After installation you're going to want to at least touch these points in your n
 
 # Password change
 
-After installation you're going to want to change your ZFS encryption password.
+After installation you're going to want to change your ZFS encryption password (unless you preconfigured a good zpool password in a settings file per [Passwords](#passwords)). At any rate you still want to be familiar with the process and its caveat in case you ever need a zpool password change or want to do one now.
 
 ## Steps
 
@@ -257,7 +460,7 @@ In order to generate a new master key after you've changed your user key as ment
         --large-block \
         --compressed \
         'zpool/root/archlinux-sxu@rekey' | \
-
+    \
     zfs receive \
         -Fvu \
         -o 'encryption=on' \
@@ -477,7 +680,12 @@ arch-chroot /mnt /bin/bash
 When done exit `chroot` and cleanly remove your work:
 
 ```
+# UEFI system ...
 umount /mnt/efi
+
+# ... or legacy BIOS system
+umount /mnt/boot/syslinux
+
 zfs umount -a
 zpool export zpool
 ```