# Installation Laying the foundation # Base System ## Setting up mirrors The Arch installation environment comes with `reflector`, a tool that generates mirror lists for `pacman`. At boot time, `reflector` is executed once to include the most recently synced mirrors and sorts them by download rate. This file will be copied to the installation destination later on. `reflector` allows for a few filtering options: | Filter | Description | | ------------------ | ------------------------------------------------------------------------------------------------------- | | `--age n` | Only return mirrors that have synchronized in the last _n_ hours. | | `--country NAME` | Restrict mirrors to selected countries, e.g. `France,Germany` (check available with `--list-countries`) | | `--fastest n` | Return the _n_ fastest mirrors that meet the other criteria. Do not use without filters! | | `--latest n` | Limit the list to the _n_ most recently synchronized servers. | | `--score n` | Limit the list to the _n_ servers with the highest score. | | `--number n` | Return at most _n_ mirrors. | | `--protocol PROTO` | Restrict protocol used by mirrors. Either `https`, `http`, `ftp` or a combination (comma-separated) | To have `reflector` generate a list of mirrors from Germany, which synced in the past 12 hours and use HTTPS for transfer: ~~~bash reflector --country Germany --age 12 --protocol https --save /etc/pacman.d/mirrorlist ~~~ ## Parallel downloads By default, `pacman` downloads packages one-by-one. If you have a fast internet connection, you can configure `pacman` to download packages in parallel, which can speed up installation significantly. Open `/etc/pacman.conf`, uncomment the line `#ParallelDownloads = 5` and set it to a value of your preference: ~~~ ... # Misc options #UseSyslog #Color #NoProgressBar CheckSpace #VerbosePkgLists ParallelDownloads = 10 #DisableSandbox ... ~~~ Alternatively, replace the settings directly with `sed` (e.g. setting 10 parallel downloads at a time): ~~~bash sed -i "/etc/pacman.conf" -e "s|^#ParallelDownloads.*|&\nParallelDownloads = 10|" ~~~ ## Installing base packages The absolute minimum set of packages required to install Arch Linux onto a machine is as follows: ~~~bash pacstrap /mnt base linux linux-firmware ~~~ However, this selection lacks the tooling required for file systems, RAID, LVM, special firmware for devices not included with `linux-firmware`, networking software, a text editor or packages necessary to access documentation. It also lacks CPU microcode packages with stability and security updates. The following table contains additional packages you most likely want to append to the above `pacstrap` command: | Package | Description | |------------------|-------------------------------------------------------------------------------------------------------------------| | `base` | Absolute essentials **(required)** | | `linux` | Vanilla Linux kernel and modules, with a few patches applied **(required)** | | `linux-hardened` | A security-focused Linux kernel applying a set of hardening patches to mitigate kernel and userspace exploits | | `linux-lts` | Long-term support (LTS) Linux kernel and modules | | `linux-zen` | Result of a collaborative effort of kernel hackers to provide the best Linux kernel possible for everyday systems | | `linux-firmware` | Device firmware files, e.g. WiFi **(required)** | | `intel-ucode` | Intel CPU microcode **(required, if on Intel)** | | `amd-ucode` | AMD CPU microcode **(required, if on AMD)** | | `btrfs-progs` | Userspace tools to manage btrfs filesystems | | `dosfstools` | Userspace tools to manage FAT filesystems | | `exfatprogs` | Userspace tools to manage exFAT filesystems | | `f2fs-tools` | Userspace tools to manage F2FS filesystems | | `e2fsprogs` | Userspace tools to manage ext2/3/4 filesystems | | `jfsutils` | Userspace tools to manage JFS filesystems | | `nilfs-utils` | Userspace tools to manage NILFS2 filesystems | | `ntfs-3g` | Userspace tools to manage NTFS filesystems | | `udftools` | Userspace tools to manage UDF filesystems | | `xfsprogs` | Userspace tools to manage XFS filesystems | | `lvm2` | Userspace tools for Logical Volume Management | | `cryptsetup` | Userspace tools for encrypting storage devices (LUKS) | | `networkmanager` | Comprehensive network management and configuration suite | | `nano` | Console text editor | | `man` | Read documentation (**man**uals) | | `sudo` | Execute commands with elevated privileges |

CAUTION: If you have an AMD CPU, include the amd-ucode package. If you have an Intel CPU, include the intel-ucode package!

ATTENTION: Include the cryptsetup package if you've encrypted your disks!

A desireable selection of packages for a base system with an AMD CPU, btrfs filesystem, UEFI ESP, LUKS disk encryption, a basic text editor, a network manager and tools for system maintenance as regular user would look something like this: ~~~bash pacstrap -K /mnt base linux linux-firmware amd-ucode btrfs-progs dosfstools cryptsetup nano networkmanager sudo ~~~ Generate the `fstab` containing information about which storage devices should be mounted at boot: ~~~bash # Generate fstab referencing UUIDs of devices/partitions genfstab -U /mnt >> /mnt/etc/fstab ~~~ Switch into the newly installed system with `arch-chroot` and continue setting it up: ~~~bash arch-chroot /mnt ~~~ # Time Zone & Locale ## Time zone Use `timedatectl` to check which time zone your system is currently set to: ~~~ Local time: Tue 2025-09-23 20:04:39 UTC Universal time: Tue 2025-09-23 20:04:39 UTC RTC time: Tue 2025-09-23 20:04:39 Time zone: UTC (UTC, +0000) System clock synchronized: yes NTP service: active RTC in local TZ: no ~~~ If the time zone doesn't match with the one you live in (e.g. if it says UTC), use the `set-timezone` command to change it:

NOTE: To list all available time zones, use the list-timezones command. Search for town names with / (search is case-sensitive). Alternatively, there's a website to help you pick the correct one by country.

~~~bash timedatectl set-timezone Europe/Berlin ~~~ ## Localization Edit `/etc/locale.gen` and uncomment `en_US.UTF-8 UTF-8` and other desired locales (prefer UTF-8): ~~~bash nano /etc/locale.gen ~~~

NOTE: You can search in nano using CTRL + W.

Generate the locales by running: ~~~bash locale-gen ~~~ Set which locales and keyboard layout the system should use for messages and documentation (`man` pages): ~~~bash echo "LANG=de_DE.UTF-8" > /etc/locale.conf echo "KEYMAP=de-latin1" > /etc/vconsole.conf ~~~ # Network Set up the default host name of the machine as well as `localhost`:

NOTE: sebin-desktop is used as an example here. Set $HOSTNAME to whatever you like.

~~~bash # Define an environment variable containing the desired hostname export HOSTNAME='sebin-desktop' # Set the hostname of the machine echo "$HOSTNAME" > /etc/hostname # Set localhost to resolve to the machine's loopback address echo "127.0.0.1 localhost" >> /etc/hosts echo "::1 localhost" >> /etc/hosts ~~~ ## Set wireless region If your machine has Wi-Fi it is advisable to set the region for wireless radio waves to comply with local regulations. Not doing this will limit you to 2.4 GHz Wi-Fi, which will likely under-utilize the Wi-Fi bandwidth on your device. Install `wireless-regdb` for utilities: ~~~bash pacman -S wireless-regdb ~~~ To set your region temporarily, e.g. Germany: ~~~bash iw reg set DE ~~~ To set it permanently, uncomment the line with your country in the file `/etc/conf.d/wireless-regdom`. Remember to rebuild your initramfs with `mkinitcpio -P` to apply the changes when the system boots. ## Network manager Previously we installed NetworkManager as our default network mangaging software. GNOME and KDE have out of the box support for managing network connections in their settings dialogs in a graphical manner. Both rely on NetworkManager. Enable NetworkManager to start at boot: ~~~bash systemctl enable NetworkManager ~~~ ### Using `iwd` as the Wi-Fi backend (optional) By default NetworkManager uses `wpa_supplicant` for managing Wi-Fi connections. `iwd` (iNet wireless daemon) is a wireless daemon for Linux written by Intel. The core goal of the project is to optimize resource utilization by not depending on any external libraries and instead utilizing features provided by the Linux Kernel to the maximum extent possible. To enable the [experimental iwd backend](https://iwd.wiki.kernel.org/networkmanager), first install `iwd` and then create a configuration file: ~~~bash pacman -S iwd nano /etc/NetworkManager/conf.d/wifi_backend.conf ~~~ Set the following in the configuration file: ~~~ [device] wifi.backend=iwd ~~~ When NetworkManager starts, it will now use `iwd` for managing wireless connections. ## IPv6 Privacy Extensions By default, Arch enables IPv6, but with the actual public IP address exposed. IPv6 includes the MAC address of the network interface. IPv6 Privacy Extensions mangle the public IP address in a way that prevents the actual address from being known publicly. Enabling IPv6 Privacy Extensions can be done in different ways: 1. via `sysctl` parameters, setting it at the lowest level 1. via NetworkManager If not set via the global NetworkManager config or a connection profile (i.e. per connection setting), NetworkManager uses sysfs to determine if IPv6 Privacy Extensions should be enabled. ### `sysctl` To enable IPv6 Privacy Extensions via sysfs during boot, `sysctl` parameters in a config file can be used. There are 3 parameters by which control behavior:

NOTE: The spelling for the parameter temp_prefered_lft is not a typo!

| Name | Value | Description | |---------------------|-------:|---------------------------------------------------------------------------| | `use_tempaddr` | 2 | 0 = disabled, 1 = enable, prefer real IP, 2 = enable, prefer temporary IP | | `temp_prefered_lft` | 86400 | Preferred life time of temporary IP in seconds (default = 1 day) | | `temp_valid_lft` | 604800 | Maximum life time of temporary IP in seconds (default = 7 days) | These parameters can be applied to: 1. set the parameter on `all` connections 1. set the parameter on the `default` connection 1. set the parameter on a specific network interface (`nic`) Create a config file such as `/etc/sysctl.d/40-ipv6.conf` and choose your parameter values for one of the three ways of setting up IPv6 Privacy extensions. For **all** network interfaces: ~~~ # Enable IPv6 Privacy Extensions net.ipv6.conf.all.use_tempaddr = 2 net.ipv6.conf.all.temp_prefered_lft = 86400 net.ipv6.conf.all.temp_valid_lft = 604800 ~~~ For the **default** network interface: ~~~ # Enable IPv6 Privacy Extensions net.ipv6.conf.default.use_tempaddr = 2 net.ipv6.conf.default.temp_prefered_lft = 86400 net.ipv6.conf.default.temp_valid_lft = 604800 ~~~ For a specific network interface, e.g. the first Wi-Fi adapter called **wlan0**: ~~~ # Enable IPv6 Privacy Extensions net.ipv6.conf.wlan0.use_tempaddr = 2 net.ipv6.conf.wlan0.temp_prefered_lft = 86400 net.ipv6.conf.wlan0.temp_valid_lft = 604800 ~~~ ### NetworkManager

NOTE: If you set up IPv6 Privacy Extensions via sysctl config, NetworkManager will use it automatically.

NetworkManager can be set up to enable IPv6 Privacy Extensions. This can either be done globally or per connection profile. To enable it **globally** create the config file `/etc/NetworkManager/conf.d/ip6-privacy.conf` with the following contents: ~~~ini [connection] ipv6.ip6-privacy=2 ~~~ This will apply the setting across all current and future connections. To enable it only **for specific connections**, open the connection profile, e.g. `/etc/NetworkManager/system-connections/.nmconnection`, look for the `[ipv6]` section in the file and add the following: ~~~ini ... [ipv6] ... ip6-privacy=2 ... ~~~ Connection profile files are named the same as their corresponding network, so `Wired Connection 1.nmconnection` or the name of any Wi-Fi network you ever connected to. When you connect to a new network, you will have to apply these settings again for the new connection. ## `systemd-resolved` for DNS name resolution `systemd-resolved` is a `systemd` service that provides network name resolution to local applications via a D-Bus interface, the `resolve` NSS service, and a local DNS stub listener on `127.0.0.53`. Benefits of using `systemd-resolved` include: * `resolvectl` as the primary single command for interfacing with the network name resolver service * A system-wide DNS cache for speeding up subsequent name resolution requests * Split DNS when using VPNs, which can help in preventing DNS leaks when connecting to multiple VPNs (See [Fedora Wiki](https://fedoraproject.org/wiki/Changes/systemd-resolved#Benefit_to_Fedora) for a detailed explenation why this is important) * Integrated DNSSEC capabilities to verify the authenticity and integrity of name resolution requests, e.g. to prevent [cache poisoning/DNS hijacking](https://en.wikipedia.org/wiki/DNS_hijacking) * DNS over TLS for further securing name resolution requests by encrypting them, improving privacy (not to be confused with DNS over HTTPS) To use `systemd-resolved` enable the respective unit: ~~~bash systemctl enable systemd-resolved ~~~ To provide domain name resolution for software that reads `/etc/resolv.conf` directly, such as web browsers and GnuPG, `systemd-resolved` has four different modes for handling the file * **stub:** a symlink to the `systemd-resolved` managed file `/run/systemd/resolve/stub-resolv.conf` containing only the stub resolver and search domains * **static:** a symlink to the static `systemd-resolved` owned file `/usr/lib/systemd/resolv.conf` containing only the stub resolver, but no search domains * **uplink:** a symlink to the `systemd-resolved` managed file `/run/systemd/resolve/resolv.conf` containing all upstream DNS servers known to `systemd-resolved`, effectively bypassing the stub resolver * **foreign:** an external tool managing system-wide DNS entries for `systemd-resolved` to derive its DNS configuration from The recommended mode is *stub.*

ATTENTION: A few notes about setting this up:

This propagates the `systemd-resolved` managed configuration to all clients. To use it, replace `/etc/resolv.conf` with a symbolic link to it: ~~~bash ln -sf ../run/systemd/resolve/stub-resolv.conf /etc/resolv.conf ~~~ When set up this way, NetworkManager automatically picks up `systemd-resolved` for network name resolution. ### Fallback DNS servers If `systemd-resolved` does not receive DNS server addresses from the network manager and no DNS servers are configured manually, then `systemd-resolved` falls back to a hardcoded list of DNS servers. The fallback order is: 1. Cloudflare 1. Quad9 (without filtering and without DNSSEC) 1. Google

ATTENTION: Depending on your use-case, you might not want to route all your DNS traffic through the pre-determined fallback servers for privacy reasons. Do your own research on fallback DNS servers that you want to trust.

Fallback addresses can be manually set in a drop-in config file, e.g. `/etc/systemd/resolved.conf.d/fallback_dns.conf`: ~~~ [Resolve] FallbackDNS=127.0.0.1 ::1 ~~~ To disable the fallback DNS functionality set the `FallbackDNS` option without specifying any addresses: ~~~ [Resolve] FallbackDNS= ~~~ ### DNSSEC

WARNING: DNSSEC support in systemd-resolved is considered experimental and incomplete.

DNSSEC is an extension to the DNS system that verifies DNS entries via authentification and data integrity checks to prevent DNS cache poisoning, but *does not **encrypt** DNS queries*. For actually encrypting your DNS traffic, see the section below. `systemd-resolved` can be configured to use DNSSEC for validation of DNS requests. It can be configured in three modes: | Setting | Description | |-------------------|------------------------------------------------------------------------------------------| | `allow-downgrade` | Validate DNSSEC only if the upstream DNS server supports it | | `true` | Always validate DNSSEC, breaking DNS resolution if the server does not support it | | `false` | Disable DNSSEC validation entirely | Set up DNSSEC in a drop-in config file, e.g. `/etc/systemd/resolved.conf.d/dnssec.conf`: ~~~ [Resolve] DNSSEC=allow-downgrade ~~~ ### DNS over TLS DNS over TLS (DoT) is a security protocol for encrypting DNS queries and responses via Transport Layer Security (TLS), thereby increasing privacy and security by preventing eavesdropping on DNS requests by internet service providers and malicious actors in man-in-the-middle attack scenarios. DNS over TLS in `systemd-resolved` is disabled by default. To enable validation of your DNS provider's server certificate, include their hostname in the `DNS` setting in the format `ip_address#hostname` and set `DNSOverTLS` to one of three modes: | Setting | Description | |-----------------|-------------------------------------------------------------------------------------------------------| | `opportunistic` | Attempt DNS over TLS when possible and fall back to unencrypted DNS if the server does not support it | | `true` | Always use DNS over TLS, breaking resolution if the server does not support it | | `false` | Disable DNS over TLS entirely |

ATTENTION: When setting DNSOverTLS=opportunistic systemd-resolved will try to use DNS over TLS and if the server does not support it fall back to regular DNS. Note, however, that this opens you to "downgrade" attacks, where an attacker might be able to trigger a downgrade to non-encrypted mode by synthesizinig a response that suggests DNS over TLS was not supported.

WARNING: If setting DNSOverTLS=yes and the server provided in DNS= does not support DNS over TLS all DNS requests will fail!

To enable DNS over TLS system-wide for all connections, add your DNS over TLS capable servers in a drop-in config file, e.g. `/etc/systemd/resolved.conf.d/dns_over_tls.conf`: ~~~ [Resolve] DNS=9.9.9.9#dns.quad9.net 149.112.112.112#dns.quad9.net [2620:fe::fe]#dns.quad9.net [2620:fe::9]#dns.quad9.net DNSOverTLS=yes ~~~ Alternatively, you can use drop-in configuration files for NetworkManager to instruct it to use DNS over TLS per connection. You can save this as a drop-in configuration file under `/etc/NetworkManager/conf.d/dns_over_tls.conf` to apply it to current and future connections or on a per-connection basis to an existing connection profile under `/etc/NetworkManager/system-connections/*.nmconnection` (as `root`). There's three possible values: * 2 = DNS over TLS always on (fail if DoT is unavailable) * 1 = opportunistic DNS over TLS (downgrades to unencrypted DNS if DoT is unavailable) * 0 = never use DNS over TLS Add or modify ~~~ini [connection] dns-over-tls=2 ~~~ ### Multicast DNS `systemd-resolved` is capable of working as a [multicast DNS](https://en.wikipedia.org/wiki/Multicast_DNS) (mDNS) resolver and responder. The resolver provides hostname resolution using a "*hostname*.local" naming scheme. mDNS support in `systemd-resolved` is enabled by default. For a given connection, mDNS will only be activated if both mDNS in `systemd-resolved` is enabled, and if the configuration for the currently active network manager enables mDNS for the connection. The `MulticastDNS` setting in `systemd-resolved` can be set to one of the following: | Setting | Description | |-----------|-------------------------------------------------------------| | `resolve` | Only enables resolution support, but responding is disabled | | `true` | Enables full mDNS responder and resolver support | | `false` | Disables both mDNS responder and resolver |

ATTENTION: If you plan on using systemd-resolved as mDNS resolver and responder consider the following:

To enable mDNS for a connection managed by NetworkManager tell `nmcli` to modify an existing connection: ~~~bash nmcli connection modify CONNECTION_NAME connection.mdns yes ~~~

TIP: The default for all NetworkManager connections can be set by creating a configuration file in /etc/NetworkManager/conf.d/ and setting connection.mdns=2 (equivalent to "yes") in the [connection] section.

[connection]
connection.mdns=2
## Avahi Avahi implements zero-configuration networking (zeroconf), allowing for multicast DNS/DNS-SD service discovery. This enables programs to publish and discover services and hosts running on a local network, e.g. network file sharing servers, remote audio devices, network printers, etc. Some desktop environments pull in the `avahi` package as a dependency. It enables their file manager to scan the network for services and make them easily accessible.

ATTENTION: If you plan on using avahi as mDNS resolver and responder consider the following:

Avahi provides local hostname resolution using a "*hostname*.local" naming scheme. To use it, install the `avahi` and `nss-mdns` package and enable Avahi: ~~~bash pacman -S avahi nss-mdns systemctl enable avahi-daemon ~~~ Then, edit the file `/etc/nsswitch.conf` and change the `hosts` line to include `mdns_minimal [NOTFOUND=return]` before `resolve` and `dns`: 
hosts: mymachines mdns_minimal [NOTFOUND=return] resolve [!UNAVAIL=return] files myhostname dns
To discover services running in your local network: ~~~bash avahi-browse --all --ignore-local --resolve --terminate ~~~ To query a specific host for the services it advertises: ~~~bash avahi-resolve-host-name hostname.local ~~~ Avahi also includes the `avahi-discover` graphical utility that lists the various services on your network. # Root Password Set the password for the `root` user: ~~~bash passwd ~~~ This password schould differ from the regular user password for security reasons. In the case of system recovery operations the `root` user comes into play, e.g. when the kernel fails to mount the root file system or system maintenance via `chroot` is needed. # sudo `sudo` is the standard tool for gaining temporary system administrator privileges on Linux to perform administrative tasks. This eliminates the need to change the current user to `root` to perform these tasks. To allow regular users to execute commands with elevated privileges, the configuration for `sudo` needs to be modified to allow this. `sudo` supports configuration drop-in files in `/etc/sudoers.d/`. Using these makes it easy to modularize the configuration and remove offending files, if something goes wrong.

TIP: File names starting with . or ~ will get ignored. Use this to turn off certain configuration settings if you need to.

WARNING: Drop-in files are just as fragile as /etc/sudoers! It is therefore strongly advised to always use visudo when creating or editing sudo config files, as it will check for syntax errors. Failing to do so will risk rendering sudo inoperable!

Create a new drop-in file at: ~~~bash EDITOR=nano visudo /etc/sudoers.d/01_wheel ~~~ The contents of the drop-in file are as follows: ~~~ ## Allow members of group wheel to execute any command %wheel ALL=(ALL:ALL) ALL ~~~ Save and exit. Now every user who is in the `wheel` user group is allowed to run any command as `root`. # zsh `zsh` is a modern shell with lots of customizability and features. Install the following packages: ~~~bash pacman -S zsh zsh-autosuggestions zsh-completions zsh-history-substring-search zsh-syntax-highlighting ~~~ | Package | Description | |--------------------------------|----------------------------------------------------------------------------------------------| | `zsh-autosuggestions` | Suggests commands as you type based on history and completions | | `zsh-completions` | Additional completion definitions for `zsh` | | `zsh-history-substring-search` | Type any part of any command from history and cycle through matches | | `zsh-syntax-highlighting` | Highlights commands whilst they are typed, helping in reviewing commands before running them | # Add User It is advised to add a regular user account for day to day usage. Add a new user, create a home directory, add them to the wheel group, set their default shell to zsh: ~~~bash useradd -mG wheel -s /bin/zsh sebin ~~~ Set a password for the new user: ~~~bash passwd sebin ~~~ # AUR Helper An AUR helper is a tool that automates the process of installing packages from the [Arch User Repository](https://aur.archlinux.org/). It does this by automating the following tasks: * search the AUR for published packages * resolve dependencies for AUR packages * retrieval and build of AUR packages * show user comments * submission of AUR packages AUR packages are distributed in the form of `PKGBUILD`s that contain information on how the package needs to be built, what dependencies is needs and all the usual metadata associated with every other Arch Linux package. [Arch Wiki](https://wiki.archlinux.org/title/AUR_helpers) has a list of AUR helpers with comparison tables ## Installation The installation procedure for any AUR helper is largely the same, as they are all published on the AUR itself. Building packages from the AUR manually will at minimum require the `base-devel` and `git` packages: ~~~bash pacman -S base-devel git ~~~

ATTENTION: If you'rere currently logged in as the root user, you need to switch to a regular user profile with su username, as makepkg will not allow you to run it as root.

Change to a temporary directory, clone the AUR helper of your choice with `git`, change into the newly created directory and call `makepkg` to build and install it, e.g. `yay`: ~~~bash cd /tmp git clone https://aur.archlinux.org/yay cd yay makepkg -si ~~~ `makepkg -si` will prompt you to install any missing dependencies for your chosen AUR helper, i.e. `go` for `yay`, `rust` for `paru`, etc. and call `pacman` to install the helper for you after the build has finished. ## Configuration `makepkg` can be configured to make better use of available system resources, improving build times and efficiency. One of these optimizations is instructing `makepkg` to pass specific options to compilers. You can either edit the main configuration file of `makepkg` at `/etc/makepkg.conf` or supply a drop-in config file in `/etc/makepkg.conf.d/*.conf` — the latter is recommended in case building starts to act strangely and you want to quickly be able to revert changes by deleting drop-in config files. ### Optimizing builds By default, `makepkg` is configured to produce generic builds of software packages. Since `makepkg` will mostly be used to build packages for your own personal machine, compiler options can be tweaked to produce optimized builds for the machine they're getting built on. For example, create a drop-in config file `/etc/makepkg.conf.d/cflags.conf` with the following contents: ~~~bash CFLAGS="-march=native -O2 -pipe -fno-plt -fexceptions \ -Wp,-D_FORTIFY_SOURCE=3 -Wformat -Werror=format-security \ -fstack-clash-protection -fcf-protection \ -fno-omit-frame-pointer -mno-omit-leaf-frame-pointer" ~~~ This will cause GCC to automatically detect and enable safe architecture-specific optimizations. The same thing can be applied to the Rust compiler. There is already a drop-in config file at `/etc/makepkg.conf.d/rust.conf` that can be edited: ~~~bash RUSTFLAGS="-C opt-level=2 -C target-cpu=native" ~~~ The `opt-level` parameter can be set to different values ranging in different levels of optimizations that will have an impact on build time. See the [Rust docs](https://doc.rust-lang.org/rustc/codegen-options/index.html#opt-level) for details. Additionally, the `make` build system can also be optimized with the `MAKEFLAGS` variable. One such optimization is to increase the number of jobs that can run simultaneously. Create a drop-in config file `/etc/makepkg.conf.d/make.conf` with the following contents: ~~~bash MAKEFLAGS="--jobs=$(nproc)" ~~~ This will prompt `make` to utilize the maximum number of CPU cores to run build jobs.

ATTENTION: Some PKGBUILDs specifically override this with -j1, because of race conditions in certain versions or simply because it is not supported in the first place. If a package fails to build you should report this to the package maintainer.

### Prevent build of `-debug` packages By default, `makepkg` is configured to also generate debug symbol packages. This affects all AUR helpers. To turn this behavior off, modify the `OPTIONS` array by either removing the `debug` option or disabling it with a `!` in front of it: ~~~bash OPTIONS=(strip docs !libtool !staticlibs emptydirs zipman purge !debug lto) ~~~ ### Using the mold linker `mold` is a drop-in replacement for `ld`/`lld` linkers, which claims to be significantly faster. Install `mold` from the repositories: ~~~bash pacman -S mold ~~~ To use `mold`, append `-fuse-ld=mold` to `LDFLAGS`: ~~~bash LDFLAGS="-Wl,-O1 -Wl,--sort-common -Wl,--as-needed -Wl,-z,relro -Wl,-z,now \ -Wl,-z,pack-relative-relocs -fuse-ld=mold" ~~~ This also needs to be passed to `RUSTFLAGS`: ~~~bash RUSTFLAGS="-C opt-level=2 -C target-cpu=native -C link-arg=-fuse-ld=mold" ~~~ ### Compression options By default, `makepkg` will compress built packages with zstd. This is controlled by the `PKGEXT` variable. The compression algorithm used is inferred from the archive extension. To speed up the packaging process, you might consider turning off the compression at the expense of increased storage usage in the package cache: ~~~bash PKGEXT='.pkg.tar' ~~~ If you need to conserve space, consider keeping compression enabled, but increasing the number of utilized cores by telling `zstd` to count logical cores instead of physical ones with `--auto-threads=logical`: ~~~bash COMPRESSZST=(zstd -c -T0 --auto-threads=logical -) ~~~ You can also increase the level of compression applied at the expense of longer packaging time, ranging from 1 (weakest) to 19 (strongest), default is 3: ~~~bash COMPRESSZST=(zstd -c -T0 -19 --auto-threads=logical -) ~~~ Or use the LZ4 algorithm, which is optimized for speed: ~~~bash PKGEXT='.pkg.tar.lz4' ~~~ ### Build entirely in RAM You can pass `makepkg` a different directory for building packages. Since building causes a lot of rapid small file access, performance could be improved by moving this process to a `tmpfs` location that is held entirely in RAM. The variable `BUILDDIR` can be used to instruct `makepkg` to build packages in another location: ~~~bash BUILDDIR=/tmp/makepkg ~~~ Since `/tmp` is such a `tmpfs` files in this directory are held in RAM. Building packages completely in RAM can therefore speed up data access and help preserve the durability of flash-based storage mediums like SSDs. # zram The zram kernel module provides a compressed block device in RAM. If you use it as swap device, the RAM can hold much more information but uses more CPU. Still, it is much quicker than swapping to a hard drive. If a system often falls back to swap, this could improve responsiveness. Using zram is also a good way to reduce disk read/write cycles due to swap on SSDs. Install the `zram-generator` package and copy the example configuration: ~~~bash pacman -S zram-generator cp /usr/share/doc/zram-generator/zram-generator.conf.example /etc/systemd/zram-generator.conf ~~~ Edit the copy of the example configuration to your liking. Comments explain what each setting does. # Boot Loader ## `systemd-boot` `systemd` comes with `systemd-boot` already, so no additional packages need to be installed. ### Install

ATTENTION: By default, systemd-boot will install itself to either of the well-known ESP locations, e.g. /efi, /boot, or (discouraged) /boot/efi. If your ESP is mounted somewhere else pass the localtion with the --esp-path parameter. $ESP refers to this location. Adjust paths accordingly!

WARNING: bootctl will not operate on UEFI variables which store boot entries when running in regular arch-chroot, which could leave your machine unbootable. Enter a chroot environement with arch-chroot -S instead.

Install `systemd-boot` by simply invoking `bootctl` with the `install` command: ~~~bash bootctl install ~~~ This will do the following: * Create the directory `$ESP/EFI/Linux` * Copy `/usr/lib/systemd/boot/efi/systemd-bootx64.efi` to `$ESP/EFI/systemd/systemd-bootx64.efi` * Copy `/usr/lib/systemd/boot/efi/systemd-bootx64.efi` to `$ESP/EFI/BOOT/BOOTX64.EFI` * Create a 32 byte random seed file at `$ESP/loader/random-seed` * Create an EFI boot entry named *Linux Boot Manager* at the top of firmware boot entries

NOTE: If a signed version of systemd-bootx64.efi exists as systemd-bootx64.efi.signed in the source directory (i.e. for Secure Boot), the signed file is copied instead.

NOTE: bootctl may complain about your ESP's mount point and the random seed file as being "world accessible". This is to let you know your ESP's current file system permissions are too lenient. To solve this, change the fmask and dmask mount options for your ESP in /etc/fstab from 0022 to 0077. Changes apply on next boot. See also: mount(8) $ Mount options for fat. If you plan on using systemd's GPT auto-mounting feature, it will set the appropriate file system permissions for you.

### Configure `systemd-boot` has two kinds of configs: * `$ESP/loader/loader.conf`: Configuration file for the boot loader itself * `$ESP/loader/entries/*.conf`: Configuration files for individual boot entries #### Boot loader config

NOTE: For a full list of options and their explanation refer to loader.conf(5) § OPTIONS

The most important options for the boot loader are as follows: | Setting | Type | Description | |-----------------|----------------|---------------------------------------------------------------------------------------------| | `default` | string | The pre-selected default boot entry. Can be pre-determined value, file name or glob pattern | | `timeout` | number | Time in seconds until the default entry is automatically booted | | `console-mode` | number/string | Display resolution mode (`0`, `1`, `2`, `auto`, `max`, `keep`) | | `auto-entries` | number/boolean | Show/hide other boot entries found by scanning the boot partition | | `auto-firmware` | number/boolean | Show/hide "Reboot into firmware" entry | An example loader configuration could look something like this:

ATTENTION: Only spaces are accepted as white-space characters for indentation, do not use tabs!

~~~ default arch # pre-selects entry from $ESP/loader/entries/arch.conf timeout 3 # 3 seconds before the default entry is booted auto-entries 1 # shows boot entries which were auto-detected auto-firmware 1 # shows entry "Reboot into firmware" console-mode max # picks the highest-numbered mode available ~~~ #### Boot entry config

SEE ALSO: The Boot Loader Specification for a comprehensive overview of what systemd-boot implements.

Available parameters in boot entry config files: | Key | Value | Description | |----------------------|--------|--------------------------------------------------------------------------------| | `title` | string | The name of the entry in the boot menu (optional) | | `version` | string | Human readable version of the entry (optional) | | `machine-id` | string | The unique machine ID of the computer (optional) | | `sort-key` | string | Used for sorting entries (optional) | | `linux` | path | Location of the Linux kernel (relative to ESP) | | `initrd` | path | Location of the Linux initrd image (relative to ESP) | | `efi` | path | Location of an EFI executable, hidden on non-EFI systems | | `options` | string | Kernel command line parameters | | `devicetree` | path | Binary device tree to use when executing the kernel (optional) | | `devicetree-overlay` | paths | List of device tree overlays. If multiple, separate by space, applied in order | | `architecture` | string | Architecture the entry is intended for (`IA32`, `x64`, `ARM`, `AA64`) | ##### Type 1 (text file based)

NOTE: As of mkinitramfs v38, the CPU microcode is embedded in the initramfs and it is no longer necessary to specify CPU microcode images on a separate initrd line before the actual initramfs.

Type 1 entries specify their parameters in `*.conf` files under `§ESP/loader/entries/`. All paths in these configs are relative to the ESP, e.g. if the ESP is mounted at `/boot` a boot loader entry located at `$ESP/loader/entries/arch.conf` would look like this: ~~~ title Arch Linux linux /vmlinuz-linux initrd /initramfs-linux.img options rd.luks.name=XXXXXXXX-XXXX-XXXX-XXXX-XXXXXXXXXXXX=cryptroot root=/dev/mapper/cryptroot rw ~~~ ##### Type 2 (EFI executable) When using a unified kernel image, any image ending with `*.efi` placed under `$ESP/EFI/Linux/` will be automatically picked up by `systemd-boot` along with the metadata embedded in that image (e.g. title, version, etc.) If your UKIs are stored somewhere else, you will need a loader entry `*.conf` file with an `efi` key pointing `systemd-boot` to the location of the `*.efi` file on the ESP: ~~~ title Arch Linux efi /EFI/Arch/linux.efi ~~~ ## EFISTUB EFISTUB is a method of booting the kernel directly as an EFI executable by the firmware without the need for a boot loader. This can be useful in cases where you want to reduce the attack surface a boot loader can introduce, or you intend to only ever boot one image. However, some UEFI firmware implementations can be flaky, so this isn't always practical. ### Install To be able to manipulate EFI boot variables install `efibootmgr`: ~~~bash pacman -S efibootmgr ~~~ ### Configure

ATTENTION: efibootmgr cannot overwrite existing boot entries and will disregard the creation of a boot entry if one with the same label already exists. If you need to overwrite an existing entry you will need to delete it first. Call efibootmgr without any arguments to list all current boot entries:

efibootmgr

To delete an entry, note its 4-digit boot entry order and instruct efibootmgr to delete it:

efibootmgr -Bb XXXX
To create a new entry `efibootmgr` needs to know the disk and partition where the kernel image resides on the ESP. In this example, the ESP is the first partition of the block device `/dev/nvme0n1`. Kernel parameters are part of the `-u` option. The partition that holds your root file system needs to be passed as a [**persistent block device name**](https://wiki.archlinux.org/title/Persistent_block_device_naming).

NOTE: If you use LVM or LUKS, you can skip this step and supply the device mapper name since that already is persistent.

You can get the persistent block device identifier of a file system with the `blkid` command, i.e. to get the UUID of the root file system. For example, if `/dev/nvme0n1p2` is the root file system: ~~~bash blkid -s UUID -o value /dev/nvme0n1p2 ~~~ For ease of scriptability, save the values to environment variables: ~~~bash export ROOT=$(blkid -s UUID -o value /dev/nvme0n1p2) export CMDL="root=UUID=$ROOT rw add_efi_memmap initrd=\\\initramfs-linux.img" ~~~ Then create the boot entry using `efibootmgr`: ~~~bash efibootmgr -c -L "Arch Linux" -d /dev/nvme0n1 -p 1 -l /vmlinuz-linux -u $CMDL -v ~~~ #### Unified kernel image When using a **unified kernel image** you can instead just point to the UKI without needing to specify any kernel parameters via the `-u` option (as these will be part of the UKI already):

ATTENTION: If Secure Boot is enabled and the command line parameters are embedded in the UKI, the embedded command line parameters will always take precedence, even if you pass additional parameters with the -u option.

~~~bash efibootmgr -c -L "Arch Linux" -d /dev/nvme0n1 -p 1 -l "EFI\Linux\archlinux-linux.efi" -v ~~~ # initramfs The initramfs contains all the necessary programs and config files needed to bring up the machine, mount the root file system and hand off the rest of the boot process to the installed system. It can be further customized with additional modules, binaries, files and hooks for special use cases and hardware. ## Usage ### Automated image generation Every kernel in Arch Linux comes with its own *.preset* file stored in `/etc/mkinitcpio.d/` with configuration presets for `mkinitcpio`. Pacman hooks build a new image after every kernel upgrade or installation of a new kernel. ### Manual image generation To manually generate a Linux kernel image issue the following command: ~~~bash mkinitcpio -p linux ~~~ This will generate a new kernel image with the settings of the preset file `/etc/mkinitcpio.d/linux.preset`. To generate kernel images with every preset available, pass the `-P` argument: ~~~bash mkinitcpio -P ~~~ ## Configuration To customize your initramfs, place drop-in configuration files into `/etc/mkinitcpio.conf.d/`. They will override the settings in the main configuration file at `/etc/mkinitcpio.conf`. An overview of the settings you can customize: | Setting | Type | Description | |-----------------------|--------|---------------------------------------------------------------| | `MODULES` | Array | Kernel modules to be loaded before any boot hooks are run. | | `BINARIES` | Array | Additional binaries you want included in the initramfs image. | | `FILES` | Array | Additional files you want included in the initramfs image. | | `HOOKS` | Array | Hooks are scripts that execute in the initial ramdisk. | | `COMPRESSION` | String | Which tool to use for compressing the image. | | `COMPRESSION_OPTIONS` | Array | Extra arguments to pass to the `COMPRESSION` tool. |

WARNING: Do not use the COMPRESSION_OPTIONS setting, unless you know exactly what you are doing. Misuse can produce unbootable images!

### `MODULES` The `MODULES` array is used to specify modules to load before anything else is done. Here you can specify additional kernel modules needed in early userspace, e.g. file system modules (`ext2`, `reiser4`, `btrfs`), keyboard drivers (`usbhid`, `hid_apple`, etc.), USB 3 hubs (`xhci_hcd`) or "out-of-tree" modules which are not part of the Linux kernel (mainly NVIDIA GPU drivers). It is also needed to add modules for hardware devices that are not always connected but you would like to be operational from the very start if they are connected during boot.

HINT: If you don't know the name of the driver of a device, lshw can tell you what hardware uses which driver, e.g.:

*-usb:2
             description: USB controller
             product: Tiger Lake-LP USB 3.2 Gen 2x1 xHCI Host Controller
             vendor: Intel Corporation
             physical id: 14
             bus info: pci@0000:00:14.0
             version: 20
             width: 64 bits
             clock: 33MHz
             capabilities: xhci bus_master cap_list
         ->  configuration: driver=xhci_hcd latency=0
             resources: iomemory:600-5ff irq:163 memory:603f260000-603f26ffff

The second to last line starting with configuration shows the driver being used.

Example of a `MODULES` array that adds two modules to the generated image needed for keyboard input, if the keyboard is connected to a USB 3 hub, e.g. a docking station: ~~~bash MODULES=(xhci_hcd usbhid) ~~~

CAUTION: Keep in mind that adding to the initramfs increases the size of the resulting image on disk. Unless you have created your boot partition (more specifically the EFI System partition at either /efi, /boot or /boot/efi) with generous space, you should limit yourself to modules strictly needed for your system. The autodetect hook tries to detect all currently loaded modules of the running system to determine the needed modules to include by default. Only include additional modules if something doesn't work as expected.

ATTENTION: If you use an NVIDIA graphics card, the following modules are required in the MODULES array for early KMS:

MODULES=(nvidia nvidia_modeset nvidia_uvm nvidia_drm)
### `BINARIES` The `BINARIES` array holds the name of extra executables needed to boot the system. It can also be used to replace binaries provided by `HOOKS`. The executable names are sourced from the `PATH` evironment variable, associated libraries are added as well. Example of a `BINARIES` array that adds the `kexec` binary: ~~~bash BINARIES=(kexec) ~~~ This option usually only needs to be set for special use cases, e.g. when there's a binary you need included that is not already part of a member in the `HOOKS` array. ### `FILES` The `FILES` array holds the full path to arbitrary files for inclusion in the image. Example of a module configuration file to be included in the image, containting the names of modules to auto-load and optional module parameters: ~~~bash FILES=(/etc/modprobe.d/modprobe.conf) ~~~ This option usually only needs to be set for special use cases. ### `HOOKS` The `HOOKS` array is the most important setting in the file. Hooks are small scripts which describe what will be added to the image. Hooks are referred to by their name, and executed in the order they are listed in the `HOOKS` array.

HINT: For a full list of availble hooks run:

mkinitcpio -L

See the help text for a hook with:

mkinitcpio -H hook_name

Alternatively, refer to Arch Wiki for a complete rundown of all the different hooks and their recommended order.

By default, systemd will bring the whole system up start to finish. In this case bootup will be handled by systemd unit files instead of scripts. The benefit of this is faster boot times and some additional features like unlocking LUKS encrypted file systems with a TPM or FIDO2 token and automatic detection and mounting of partitions with the appropriate GUID Partition Table (GPT) UUIDs (see: [Discoverable Partition Specification](https://uapi-group.org/specifications/specs/discoverable_partitions_specification/)). The default `HOOKS` array should be enough to bring up most systems. However, if you have special use cases, additional hooks will be needed: | Hook | Description | |--------------|-------------------------------------------------------------------------------------------------| | `mdadm_udev` | Needed for assembling RAID arrays via udev (software RAID), needs the `mdadm` package installed | | `sd-encrypt` | Needed for booting from an encrypted file system, needs the `cryptsetup` package installed | | `lvm2` | Needed for booting a system that is on LVM, needs the `lvm2` package installed | One such special case is encryption, which would result in a `HOOKS` array that looks like this:

ATTENTION: The order in which hooks are placed in the array is important!

~~~bash HOOKS=(base systemd autodetect microcode modconf kms keyboard sd-vconsole block sd-encrypt filesystems fsck) ~~~

ATTENTION: In some cases it might be necessary to place the keyboard hook before the autodetect hook to be able to enter the passphrase to unlock the encrypted file systems, e.g. when using different keyboards requiring a different module from the one in use at the time of building the initramfs.

### `COMPRESSION` The `COMPRESSION` option instructs `mkinitcpio` to compress the resulting images to save on space on the EFI System Partition or `/boot` partition. This can be especially important if you include a lot of modules and hooks and the size of the image grows. Compressing the initramfs is a tradeoff between: * time it takes to compress the image * space saved * time it takes the kernel to decompress the image during boot Which one you choose is something you have to decide on the constraints you're working with (slow/fast CPU, available cores, RAM usage, disk space), but generally speaking the default `zstd` compression strikes a good balance. | Algorithm | Description | |-----------|---------------------------------------------------------------------| | `cat` | Uncompressed | | `zstd` | Best tradeoff between de-/compression time and image size (default) | | `gzip` | Balanced between speed and size, acceptable performance | | `bzip2` | Rarely used, decent compression, resource conservative | | `lzma` | Very small size, slow to compress | | `xz` | Smallest size at longer compression time, RAM intensive compression | | `lzop` | Slightly better compression than lz4, still fast to decompress | | `lz4` | Fast decompression, slow compression, "largest" compressed output |

NOTE: See this article for a comprehensive comparison between compression algorithms.

### `COMPRESSION_OPTIONS`

WARNING: Misuse of this option may lead to an unbootable system if the kernel is unable to unpack the resulting archive. Do not set this option unless you're absolutely sure that you have to!

The `COMPRESSION_OPTIONS` setting allows you to pass additional parameters for the compression tool. Available parameters depend on the algorithm chosen for the `COMPRESSION` option. Refer to the tool's manual for available options. If left empty `mkinitcpio` will make sure it always produces a working image. Additionally, `MODULES_DECOMPRESS` instructs `mkinitcpio` to decompress kernel modules prior to inclusion in the initramfs. This can further increase compression efficiency and bring down the initramfs size further. When this option is not set, compressed kernel modules are included as-is. For example, to use the maximum zstd compression level, using all available CPU cores and show verbose output during compression: ~~~bash COMPRESSION="zstd" COMPRESSION_OPTIONS=(-T0 -19 --long --auto-threads=logical -v) MODULES_DECOMPRESS="yes" ~~~ ## Unified Kernel Image A unified kernel image (UKI) combines an EFI stub image, CPU microcode, kernel command line and an initramfs into a single file that can be read and executed by the machine's UEFI firmware, thus making a boot manager potentially redundant. Additionally, it streamlines the process of signing for secure boot, as there is only a single file to sign. Version 31 of `mkinitcpio` introduced support for building UKIs out of the box. Starting with v39, `systemd-ukify` is the recommended method by which to generate UKIs. As `systemd-ukify` is *not* part of the `systemd` package, you'll have to install it manually: ~~~bash pacman -S systemd-ukify ~~~ To make `mkinitcpio` generate UKIs, edit the appropriate `*.preset` file for your kernel in `/etc/mkinitcpio.d/`: * comment out the `default_image` and `fallback_image` lines (as they won't be needed) * uncomment the `default_uki` and `fallback_uki` lines (prompts `mkinitcpio` to switch to UKI generation) * point the file path to somewhere on your EFI System Partition (e.g. `/efi`)

NOTE: mkinitcpio will automatically source command line parameters from files in /etc/cmdline.d/*.conf or a complete single command line from /etc/kernel/cmdline. If you need different images to use different kernel command line parameters, the *_options line in the *.preset allows you to pass additional arguments to mkinitcpio, i.e. the --cmdline argument to point it to a different file containing a different set of kernel command line parameters.

NOTE: Placing the UKI under /efi/EFI/Linux/ allows systemd-boot to automatically detect images and list them without having to specifically create boot entries for them.

A `*.preset` file edited for UKI generation could look something like this: ~~~bash # mkinitcpio preset file for the 'linux' package #ALL_config="/etc/mkinitcpio.conf" ALL_kver="/boot/vmlinuz-linux" #ALL_kerneldest="/boot/vmlinuz-linux" #PRESETS=('default') PRESETS=('default' 'fallback') #default_config="/etc/mkinitcpio.conf" #default_image="/boot/initramfs-linux.img" default_uki="/efi/EFI/Linux/arch-linux.efi" #default_options="--splash /usr/share/systemd/bootctl/splash-arch.bmp" #fallback_config="/etc/mkinitcpio.conf" #fallback_image="/boot/initramfs-linux-fallback.img" fallback_uki="/efi/EFI/Linux/arch-linux-fallback.efi" fallback_options="-S autodetect,plymouth --cmdline /etc/kernel/cmdline_fallback" ~~~ This `*.preset` file instructs `mkinitcpio` to generate a UKI and enables the fallback initramfs. It skips the `autodetect` and `plymouth` hooks for the fallback initramfs and passes a different set of kernel command line parameters, e.g. displaying boot logs instead of showing a splash screen. ### Kernel Command Line Parameters `mkinitcpio` automatically looks for kernel command line parameters specified in `/etc/cmdline.d/*.conf` as drop-in files or `/etc/kernel/cmdline` as a single file.

WARNING: If mkinitcpio does not find command line parameters in either of the above locations, it will fall back to reading the command line of the currently booted system from /proc/cmdline. If you're booted into the Arch installation environment, this will most likely leave you with an unbootable system. Set at least one command line parameter in one of the above locations!

Create the directory for command line parameter drop-in files and start with specifying parameters for the root file system: ~~~bash mkdir /etc/cmdline.d nano /etc/cmdline.d/root.conf ~~~ Continue by specifying the root file system via [persistent block device naming](https://wiki.archlinux.org/title/Persistent_block_device_naming) and mounting it writable: ~~~ root=UUID=XXXXXXXX-XXXX-XXXX-XXXX-XXXXXXXXXXXX rw ~~~ You can add as many `*.conf` files as you need to logically split up kernel parameters. All of the parameters from all files will be included in the UKI. #### GPT auto mounting Since the default initramfs type is systemd-based, it's possible to rely on [`systemd-gpt-auto-generator(8)`](https://man.archlinux.org/man/systemd-gpt-auto-generator.8) for automatic discovery and mounting of file systems during boot.

ATTENTION: This requires that the correct GPT partition types were set during partitioning and that the file systems to be auto mounted are located on the same disk as the EFI system partition. If other important file systems are located on other disks, they must still be specified via /etc/crypttab and /etc/fstab.

GPT auto mounting will create a symbolic link to the root file system and the encrypted file system by which it can be addressed. This can be specified in a file like `/etc/crypttab.initramfs` to be included at boot time (see [`crypttab(5)`](https://man.archlinux.org/man/crypttab.5.en) for details on the syntax):

NOTE: By default, dm-crypt does not allow TRIM for SSDs for security reasons (information leak). To override this behavior, either specify rd.luks.options=discard as an additional kernel command line parameter or add the discard option in /etc/crypttab.initramfs in the options field.

~~~ # root /dev/gpt-auto-root-luks ~~~ During boot, the system will ask for the passphrase for the encrypted file system and systemd will mount the unlocked filesystem automatically. If there are additional options you would like to pass, specify them as additional parameters in the `` column. With this type of configuration, `root` and `rd.luks` can be omitted entirely from the required list of kernel command line parameters:

ATTENTION: Be aware of the specifics of your chosen root file system. For example, when using btrfs, you will still need to specify the subvolume and any other file system options as kernel command line parameters, as automatic discovery and mounting will use the default options for mounting file systems: rootflags=noatime,compress=zstd,subvol=@.

~~~ rw ~~~ Once at least the root file system has been mounted, the boot process continues to mount file systems specified via `/etc/crypttab` and `/etc/fstab` like normal. #### Manually In cases where GPT auto mounting is not possible or undesired, the manual way of specifying encrypted devices remains available. In a systemd-based initramfs, `rd.luks.name` is used to specify the encrypted partition by its UUID and a mapper name by which the decrypted file system is made available, resulting in a kernel command line that looks like this:

NOTE: By default, dm-crypt does not allow TRIM for SSDs for security reasons (information leak). To override this behavior, either specify rd.luks.options=discard as an additional kernel command line parameter or add the discard option in /etc/crypttab.initramfs in the options field.

~~~ rd.luks.name=XXXXXXXX-XXXX-XXXX-XXXX-XXXXXXXXXXXX=root root=/dev/mapper/root rw ~~~ The UUID of the encrypted file system can be determined using `blkid` (assuming `/dev/nvme0n1p3` is the encrypted file system):

NOTE: Pressing Ctrl + T inside nano allows you to paste the result of a command at the current cursor position.

~~~bash blkid -s UUID -o value /dev/nvme0n1p3 ~~~ If you prefer a config file approach, or need to mount multiple encrypted file systems during boot, the same `/etc/crypttab.initramfs` file can be used to specify all encrypted devices. Using [persistent block device naming](https://wiki.archlinux.org/title/Persistent_block_device_naming), the file could look like this (see [`crypttab(5)`](https://man.archlinux.org/man/crypttab.5.en) for details on the syntax):: ~~~ # root UUID=XXXXXXXX-XXXX-XXXX-XXXX-XXXXXXXXXXXX ~~~ This allows for omitting any `rd.luks` parameters entirely:

ATTENTION: Be aware of the specifics of your chosen root file system. For example, when using btrfs, you will still need to specify the subvolume and any other file system options as kernel command line parameters, as automatic discovery and mounting will use the default options for mounting file systems: rootflags=noatime,compress=zstd,subvol=@.

~~~ root=/dev/mapper/root rw ~~~ # Secure Boot Secure Boot is a security feature found in the UEFI standard, designed to add a layer of protection to the pre-boot process: by maintaining a cryptographically signed list of binaries authorized or forbidden to run at boot, it helps in improving the confidence that the machine core boot components (boot manager, kernel, initramfs) have not been tampered with.

ATTENTION: When using Secure Boot it's imperative to use it with disk encryption. If the storage device that stores the keys is not encrypted, anybody can read the keys and use them to sign bootable images, thereby defeating the purpose of using Secure Boot at all. Therefore, this guide will assume disk encryption is being used.

## Preparations To determine the current state of Secure Boot execute: ~~~bash bootctl status ~~~ The output looks something like this: ~~~ System: Firmware: UEFI 2.70 (American Megatrends 5.17) Firmware Arch: x64 Secure Boot: enabled (user) TPM2 Support: yes Measured UKI: yes Boot into FW: supported ... ~~~ In order to proceed you need to set your firmware's Secure Boot mode into "setup" mode. This can usually be achieved by wiping the key store of the firmware. Refer to your mainboard's user manual on how to do this. ## Installation For the most straight-forward Secure Boot toolchain install `sbctl`: ~~~bash pacman -S sbctl ~~~ It tremendously simplifies generating Secure Boot keys, loading keys into firmware and signing kernel images. ## Generating keys

SEE ALSO: The Meaning of all the UEFI Keys

Secure Boot implementations use these keys: | Key Type | Description | |-------------------------------------|---------------------------------------------------------------------------------| | Platform Key (PK) | Top-level key | | Key Exchange Key (KEK) | Keys used to sign Signatures Database and Forbidden Signatures Database updates | | Signature Database (db) | Contains keys and/or hashes of allowed EFI binaries | | Forbidden Signatures Database (dbx) | Contains keys and/or hashes of denylisted EFI binaries | To generate new keys and store them under `/var/lib/sbctl/keys`: ~~~bash sbctl create-keys ~~~ ## Kernel Lockdown Mode To further strengthen security you might want to consider using the kernel's built-in Lockdown Mode. When engaging lockdown, access to certain features and facilities is blocked, even for the root user. This helps prevent Secure Boot from being bypassed through a compromised system, for example by editing EFI variables or replacing the kernel at runtime. Lockdown Mode knows two modes of operation: * `integrity`: kernel features that allow userland to modify the running kernel are disabled (kexec, bpf) * `confidentiality`: kernel features that allow userland to extract confidential information from the kernel are also disabled The recommended mode is `integrity`, as `confidentiality` can break certain applications (e.g. Docker). To enable Lockdown Mode, set the `lockdown=MODE` kernel command line parameter with your preferred mode. ## Enroll keys in firmware

WARNING: Replacing the platform keys with your own can end up bricking your machine, making it impossible to get into the UEFI/BIOS settings to rectify the situation. This is due to the fact that some device firmware (OpROMs, e.g. GPU firmware), that gets executed during boot, may be signed using Microsoft's keys. Run sbctl enroll-keys --microsoft if you're unsure if this applies to you (enrolling Microsoft's Secure Boot keys alongside your own custom ones) or include the TPM Event Log with sbctl enroll-keys --tpm-eventlog (if your machine has a TPM and you don't need or want Microsoft's keys) to prevent bricking your machine.

ATTENTION: Make sure your firmware's Secure Boot mode is set to setup mode! You can do this by going into your firmware settings and wiping the factory default keys. Additionally, keep an eye out for any setting that auto-restores the default keys on system start.

TIP: If you plan to dual-boot Windows, run sbctl enroll-keys --microsoft to enroll Microsoft's Secure Boot keys along with your own custom keys.

To enroll your keys, simply: ~~~bash sbctl enroll-keys ~~~ ## Automated signing of UKIs `sbctl` comes with a hook for `mkinitcpio` which runs after it has rebuilt an image. Manually specifying images to sign is therefore entirely optional. ## Signing the Bootloader

NOTE: This is the manual method. If you also want to automate the bootloader update process, skip to the section below.

If you plan on using a boot loader, you will also need to add its `*.efi` executable(s) to the `sbctl` database, e.g. `systemd-boot`: ~~~bash sbctl sign --save /efi/EFI/BOOT/BOOTX64.EFI sbctl sign --save /efi/EFI/systemd/systemd-bootx64.efi ~~~ Upon system upgrades, `pacman` will call `sbctl` to sign the files listed in the `sbctl` database. ### Automate `systemd-boot` updates and signing `systemd` comes with a `systemd-boot-update.service` unit file to automate updating the bootloader whenever `systemd` is updated. However, it only updates the bootloader **after** a reboot, by which time `sbctl` has already run the signing process. This would necessitate manual intervention. Recent versions of `bootctl` look for a `.efi.signed` file before a regular `.efi` file when copying bootloader files during `install` and `update` operations. So to integrate better with the auto-update functionality of `systemd-boot-update.service`, the bootloader needs to be signed ahead of time. ~~~bash sbctl sign --save \ -o /usr/lib/systemd/boot/efi/systemd-bootx64.efi.signed \ /usr/lib/systemd/boot/efi/systemd-bootx64.efi ~~~ This will add the source and target file paths to `sbctl`'s database. The pacman hook included with `sbctl` will trigger whenever a file in `usr/lib/**/efi/*.efi*` changes, which will be the case when `systemd` is updated and a new version of the unsigned bootloader is written to disk at `/usr/lib/systemd/boot/efi/systemd-bootx64.efi`. Finally, enable the `systemd-boot-update.service` unit: ~~~bash systemctl enable systemd-boot-update ~~~ Now when `systemd` is updated the **signed** version of the `systemd-bootx64.efi` booloader will be copied to the ESP after a reboot, completely automating the bootloader update and signing process!