From b67b843c130c7abe81684496d612966ca7a76f5a Mon Sep 17 00:00:00 2001
From: "Casper V. Kristensen" <casper@vkristensen.dk>
Date: Wed, 3 Apr 2024 00:23:45 +0200
Subject: [PATCH] /tmp on tmpfs, /var/tmp on disk

---
 modules/base/impermanence.nix | 23 +++++++++--------------
 1 file changed, 9 insertions(+), 14 deletions(-)

diff --git a/modules/base/impermanence.nix b/modules/base/impermanence.nix
index 31a492a..b79009b 100644
--- a/modules/base/impermanence.nix
+++ b/modules/base/impermanence.nix
@@ -15,25 +15,11 @@
     impermanence.nixosModules.impermanence
   ];
 
-  # We *don't* want to use tmpfs for /tmp in case we have to put big files
-  # there. Instead, we mount it to the disk and instruct systemd to clean it on
-  # boot.
-  # TODO: There might be a way to configure /tmp to be in-memory storage until
-  # it gets too big.
-  boot.tmp.cleanOnBoot = true;
-
   # Each module will configure the paths they need persisted. Here we define
   # some general system paths that don't really fit anywhere else.
   environment.persistence."/nix/persist" = {
     hideMounts = true;
     directories = [
-      # See comment above for /tmp
-      {
-        directory = "/tmp";
-        user = "root";
-        group = "root";
-        mode = "1777";
-      }
       # The uid and gid maps for entities without a static id is saved in
       # /var/lib/nixos. Persist to ensure they aren't changed between reboots.
       {
@@ -55,6 +41,15 @@
         group = "root";
         mode = "0755";
       }
+      # /var/tmp is meant for temporary files that are preserved across
+      # reboots. Some programs might store files too big for in-memory /tmp
+      # there. Files older than 10 days are cleaned by systemd.
+      {
+        directory = "/var/tmp";
+        user = "root";
+        group = "root";
+        mode = "1777";
+      }
     ];
     files = [
       "/etc/machine-id" # needed for /var/log