Each line was found once and would otherwise be found again; nothing is distribution-specific but the package manager.
Firmware
sudo pacman -S gnome-firmware
The libvirt default network
libvirt ships the default network inactive: NAT, backed by dnsmasq:
sudo pacman -S dnsmasq
sudo virsh net-list --all
sudo virsh net-autostart default
sudo virsh net-start default
net-autostart survives a reboot; net-start covers only this session.
Flameshot on Wayland
Under Wayland, Flameshot cannot grab the screen from a GNOME shortcut: no terminal to attach to. Wrapping it in script supplies one:
script --command "QT_QPA_PLATFORM=wayland flameshot gui" /dev/null
Point the custom shortcut at that, not flameshot gui. See Flameshot — Wayland help.
Low battery warning
UPower thresholds live in /etc/UPower/UPower.conf. After editing:
sudo systemctl restart upower
Emergency shell from GRUB
When the system no longer reaches a login: at the GRUB menu, highlight the entry, press e, append to the kernel command line:
init=/bin/bash
Boot with Ctrl+X. Root comes up read-only: remount before editing — /etc/fstab is the usual reason to be here:
mount -o remount,rw /
Fingerprint reader
Packages first; the AUR build covers chips stock libfprint does not (a CS9711):
sudo pacman -S polkit-gnome fprintd
yay -S libfprint-CS9711-git
Then PAM. In /etc/pam.d/sudo the first line keeps sudo usable from a real terminal without enrolled fingerprints, not a password fall-through; the second accepts the reader:
auth [success=1 default=ignore] pam_succeed_if.so service in sudo:su:su-l tty in :unknown
auth sufficient pam_fprintd.so
Polkit needs the same line in /usr/lib/pam.d/polkit-1, or GNOME dialogs ignore it:
auth sufficient pam_fprintd.so