chore: Add base configuration.

system/impermanence.nix

@@ -0,0 +1,45 @@
+{lib, ...}: {
+  fileSystems."/persist".neededForBoot = true;
+  fileSystems."/nix".neededForBoot = true;
+  boot.initrd.postDeviceCommands = lib.mkAfter ''
+    mkdir /btrfs_tmp
+    mount /dev/root_vg/root /btrfs_tmp
+    if [[ -e /btrfs_tmp/root ]]; then
+      mkdir -p /btrfs_tmp/old_roots
+      timestamp=$(date --date="@$(stat -c %Y /btrfs_tmp/root)" "+%Y-%m-%-d_%H:%M:%S")
+      mv /btrfs_tmp/root "/btrfs_tmp/old_roots/$timestamp"
+    fi
+
+    delete_subvolume_recursively() {
+      IFS=$'\n'
+      for i in $(btrfs subvolume list -o "$1" | cut -f 9- -d ' '); do
+        delete_subvolume_recursively "/btrfs_tmp/$i"
+      done
+      btrfs subvolume delete "$1"
+    }
+
+    for i in $(find /btrfs_tmp/old_roots/ -maxdepth 1 -mtime +30); do
+      delete_subvolume_recursively "$i"
+    done
+
+    btrfs subvolume create /btrfs_tmp/root
+    umount /btrfs_tmp
+  '';
+  environment.persistence."/persist" = {
+    enable = true;
+    hideMounts = true;
+    directories = [
+      "/var/log"
+      "/var/lib/nixos"
+      "/var/lib/systemd/coredump"
+      "/etc/nixos"
+      "/etc/NetworkManager"
+    ];
+    files = [
+      "/etc/machine-id"
+      "/etc/ssh/ssh_host_ed25519_key"
+      "/etc/ssh/ssh_host_ed25519_key.pub"
+      #"/var/lib/sops-nix/key.txt"
+    ];
+  };
+}