Add murk and impermanence

README.md

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+# Installation
+
+with disko-install
+
+```sh
+sudo nixos-generate-config --root /tmp/config --no-filesystems
+sudo nix run 'github:nix-community/disko/latest#disko-install' -- --flake '/tmp/config/etc/nixos#mymachine' --disk main /dev/sda
+sudo nix run 'github:nix-community/disko/latest#disko-install' -- --flake "https://codeberg.org/muon/home#$(hostname)" --disk crypted /dev/disk/by-diskseq/1
+```
+
+
+without disko-install
+
+```sh
+sudo nix --experimental-features "nix-command flakes" run github:nix-community/disko/latest -- --mode destroy,format,mount hosts/$(hostname)/disk-config.nix
+sudo mount -o subvol=/ /dev/mapper/crypted /mnt
+sudo btrfs subvolume snapshot -r /mnt/root /mnt/root-blank
+sudo nixos-generate-config --root /mnt
+mkdir -p /mnt/home/muon/src
+cd /mnt/home/muon/src
+git clone https://codeberg.org/muon/home
+cp /mnt/etc/nixos/hardware-configuration.nix /mnt/home/muon/src/home/hosts/$(hostname)/
+sudo nixos-install --root /mnt --no-root-passwd --flake /mnt/home/muon/src/home#$(hostname)
+sudo umount -R /mnt
+sudo cryptsetup close /dev/mapper/crypted
+```
+
+# Impermanence
+
+## Erasure
+
+```nix
+  boot.initrd.postResumeCommands = lib.mkAfter ''
+    mkdir /btrfs_tmp
+    mount /dev/mapper/crypted /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
+  '';
+```