Enable zram and larger nix store in a NixOS live ISO environment

nixos-iso-bootstrap.sh

#!/usr/bin/env bash

# Run this as root

zram_size=2G
if [[ "$#" -gt 0 ]]; then
  zram_size="$1"
fi

# Enable zram swap
# REF: <https://wiki.archlinux.org/title/Improving_performance#zram_or_zswap>
if ! lsmod | grep -q zram; then
  modprobe zram
  echo lz4 >/sys/block/zram0/comp_algorithm
  echo "$zram_size" >/sys/block/zram0/disksize
fi
if ! swapon --show=NAME --noheadings | grep -q /dev/zram0; then
  mkswap /dev/zram0
  swapon --priority 100 /dev/zram0
fi

# Remount tmpfs for larger nix store
mount -oremount,size=100% /nix/.rw-store

# Mount nixos if previously installed
root_part=/dev/disk/by-label/nixos-root
boot_part=/dev/disk/by-label/nixos-boot
esp_part=/dev/disk/by-label/nixos-esp
if [[ -e "$root_part" ]]; then
  mount_opt=""
  if [[ "$(lsblk -no FSTYPE "$root_part")" == btrfs ]]; then
    mount_opt=compress-force=zstd:3,noatime
  fi
  mount -o"$mount_opt" "$root_part" /mnt
  mkdir -p /mnt/boot
fi
if [[ -e "$boot_part" ]]; then
  mount "$boot_part" /mnt/boot
elif [[ -e "$esp_part" ]]; then
  mount "$esp_part" /mnt/boot
fi