From 98361e3555cd11f77c7ebe34dfa1ad1b7c7713ac Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Sol=C3=A8ne=20Rapenne?= <solene@perso.pw>
Date: Sat, 24 Jun 2023 11:31:49 +0200
Subject: [PATCH] add a reboot timer

---
 doc/reference.md |  4 +++-
 utils/bento.nix  | 18 ++++++++++++++++++
 2 files changed, 21 insertions(+), 1 deletion(-)

diff --git a/doc/reference.md b/doc/reference.md
index 5f1c7d9..e461bcc 100644
--- a/doc/reference.md
+++ b/doc/reference.md
@@ -55,7 +55,9 @@ This adds at least 8 kB of inbound bandwidth for each input when checking for ch
 
 # Auto reboot
 
-You can create a file named `REBOOT` in a host directory. When that host will rebuild the system, it will look at the new kernel, kernel modules and initrd, if they changed, a reboot will occur immediately after reporting a successful upgrade.  A kexec is used for UEFI systems for a faster reboot (this avoids BIOS and bootloader steps).
+You can create a file named `REBOOT` in a host directory.  When that host will rebuild the system, it will look at the new kernel, kernel modules and initrd, if they changed, a reboot will occur immediately after reporting a successful upgrade.  A kexec is used for UEFI systems for a faster reboot (this avoids BIOS and bootloader steps).
+
+Independently of the `REBOOT` file, in the provided `utils/bento.nix`, there is a systemd service that can be enabled to automatically reboot at a given systemd calendar if the kernel/mdoules/initrd changed.  This is more convenient for servers.
 
 # Status report of the fleet
 
diff --git a/utils/bento.nix b/utils/bento.nix
index 2e3bcc6..b4d3a73 100644
--- a/utils/bento.nix
+++ b/utils/bento.nix
@@ -17,6 +17,24 @@ in {
     restartIfChanged = false;
   };
 
+  systemd.services.bento-reboot = {
+    # this is disabled by default
+    # to avoid wrong expectations from users
+    enable = false;
+    startAt = "04:00";
+    path = with pkgs; [coreutils systemd];
+    serviceConfig.Type = "oneshot";
+    script = ''
+      booted="$(readlink /run/booted-system/{initrd,kernel,kernel-modules})"
+      built="$(readlink /nix/var/nix/profiles/system/{initrd,kernel,kernel-modules})"
+      if [ ! "$booted" = "$built" ]
+      then
+          systemctl kexec || systemctl reboot
+      fi
+    '';
+  };
+
+
   systemd.sockets.listen-update = {
     enable = true;
     wantedBy = ["sockets.target"];