nix-config/.archlinux/install-scripts/004-postinstall

#!/bin/sh
#
# Common post-install system configuration that doesn't involve any
# external packages (besides fish)
#
# https://wiki.archlinux.org/index.php/General_recommendations

set -xe

# Enable the DHCP client daemon service
arch-chroot /mnt ln -sf /usr/lib/systemd/system/dhcpcd.service \
                        /etc/systemd/system/multi-user.target.wants/dhcpcd.service

# Enable the timesync daemon service (sync the time periodically with a remote server)
arch-chroot /mnt ln -sf /usr/lib/systemd/system/systemd-timesyncd.service \
                        /etc/systemd/system/sysinit.target.wants/systemd-timesyncd.service

# Enable colors in pacman by uncommenting the Color line.
sed -i '/Color/s/^#//g' /mnt/etc/pacman.conf

# Show package upgrades as a list
sed -i '/VerbosePkgLists/s/^#//g' /mnt/etc/pacman.conf

# Give users in the wheel group permission to use sudo
echo "%wheel ALL=(ALL) ALL" >> /mnt/etc/sudoers

# Create a new user account with sudo privileges and the fish shell.
arch-chroot /mnt useradd -m -g users -G wheel -s /usr/bin/fish "$USERNAME"

# Then, set the password equal to the username (change this later).
echo "$USERNAME:$USERNAME" | chpasswd