Add new host omar

1 files changed, 32 insertions, 0 deletions

diff --git a/shared/nixos/zfs-impermenance/default.nix b/shared/nixos/zfs-impermenance/default.nix
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+++ b/shared/nixos/zfs-impermenance/default.nix
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+# This module sets up basic impermenance the way I like to do it on my ZFS
+# hosts. It assumes there is a main zpool called rpool, which has a dataset
+# `rpool/local/root` mounted at `/`, and that the dataset has an empty dataset
+# called `@blank`.
+#
+# Here is the dataset structure I use:
+#
+#    rpool
+#    ├── local
+#    │   ├── nix (atime=off, mountpoint=/nix)
+#    │   └── root (mountpoint=/)
+#    └── safe
+#        ├── home (mountpoint=/home)
+#        └── persist (mountpoint=/persist)
+#
+# I usually follow the convention that `rpool/local` isn't backed up and
+# `rpool/safe` is.
+#
+# See: https://grahamc.com/blog/erase-your-darlings/
+{lib, ...}: {
+  # Reset / to empty on boot. This is what achieves the impermenance.
+  # Unlike the holy book (the linked article), I had to use `postResumeCommands`
+  # as this is the step where ZFS imports the dataset (but doesnt't mounted it yet).
+  # See: https://github.com/NixOS/nixpkgs/blob/b681065d0919f7eb5309a93cea2cfa84dec9aa88/nixos/modules/tasks/filesystems/zfs.nix#L627-L659
+  boot.initrd.postResumeCommands = lib.mkAfter ''
+    zfs rollback -r rpool/local/root@blank
+  '';
+
+  # Filesystems with mountpoints at `/` and `/nix` are automatically mounted at boot,
+  # but `/persist` is bespoke, so we have to teach init about that one ourselves.
+  fileSystems."/persist".neededForBoot = true;
+}