toy around with explicitly spinning down the hard drive during shutdown

abandon the concept. it requires a systemd rebuild, and therefore
almost all of userspace. not worth it yet. maybe buy a powered hub.

cfg/hardware.nix

@@ -66,4 +66,37 @@
   # ondemand power scaling keeps the cpu at low frequency when idle, and sets to max frequency
   # when load is detected. (v.s. the "performance" default, which always uses the max frequency)
   powerManagement.cpuFreqGovernor = "ondemand";
+
+  # XXX colin: this allows one to `systemctl halt` and then not remove power until the HDD has spun down.
+  # however, it doesn't work with reboot because systemd will spin the drive up again to read its reboot bin.
+  # a better solution would be to put the drive behind a powered USB hub (or get a SSD).
+  systemd.services.diskguard = {
+    description = "Safely power off spinning media";
+    before = [ "shutdown.target" ];
+    wantedBy = [ "sysinit.target" ];
+    # old (creates dep loop, but works)
+    # before = [ "systemd-remount-fs.service" "shutdown.target" ];
+    # wantedBy = [ "systemd-remount-fs.service" ];
+    serviceConfig = {
+      Type = "oneshot";
+      RemainAfterExit = true;
+      ExecStart = "${pkgs.coreutils}/bin/true";
+      ExecStop = with pkgs; writeScript "diskguard" ''
+        #!${bash}/bin/bash
+        if ${procps}/bin/pgrep nixos-rebuild ;
+        then
+          exit 0  # don't halt drives unless we're actually shutting down. maybe better way to do this (check script args?)
+        fi
+        # ${coreutils}/bin/sync
+        # ${util-linux}/bin/mount -o remount,ro /nix/store
+        # ${util-linux}/bin/mount -o remount,ro /
+        # -S 1 retracts the spindle after 5 seconds of idle
+        # -B 1 spins down the drive after <vendor specific duration>
+        ${hdparm}/sbin/hdparm -S 1 -B 1 /dev/sda
+        # TODO: monitor smartmonctl until disk is idle? or try hdparm -Y
+        # ${coreutils}/bin/sleep 20
+        # exec ${util-linux}/bin/umount --all -t ext4,vfat,ext2
+      '';
+    };
+  };
 }

cfg/users.nix

@@ -32,6 +32,7 @@
       pkgs.file
       pkgs.git
       pkgs.gptfdisk
+      pkgs.hdparm
       pkgs.htop
       pkgs.iftop
       pkgs.iotop
@@ -46,6 +47,7 @@
       pkgs.parted
       pkgs.python3
       pkgs.ripgrep
+      pkgs.smartmontools
       pkgs.socat
       pkgs.sudo
       pkgs.telnet

configuration.nix

@@ -6,6 +6,7 @@
 #   nix show-config
 #   nix eval --raw <expr>  => print an expression. e.g. nixpkgs.raspberrypifw prints store path to the package
 #   nix-option   ##  query options -- including their SET VALUE; similar to search: https://search.nixos.org/options
+#   nixos-rebuild switch --upgrade   ## pull changes from the nixos channel (e.g. security updates) and rebuild
 
 { config, lib, modulesPath, pkgs, specialArgs, options }:
 
@@ -33,6 +34,8 @@ in
       pleroma = super.callPackage ./pkgs/pleroma { };
       # jackett doesn't allow customization of the bind address: this will probably always be here.
       jackett = self.callPackage ./pkgs/jackett { pkgs = super; };
+      # fix abrupt HDD poweroffs as during reboot. patching systemd requires rebuilding nearly every package.
+      # systemd = import ./pkgs/systemd { pkgs = super; };
 
       #### nixos-unstable packages
       # gitea: 1.16.5 contains a fix which makes manual user approval *actually* work.

pkgs/systemd/01-spindown-drive.patch

@@ -0,0 +1,28 @@
+diff --git a/src/shutdown/shutdown.c b/src/shutdown/shutdown.c
+index 2c3cbec02c..8eef305578 100644
+--- a/src/shutdown/shutdown.c
++++ b/src/shutdown/shutdown.c
+@@ -603,6 +603,7 @@ int main(int argc, char *argv[]) {
+                                 execv(args[0], (char * const *) args);
+ 
+                                 /* execv failed (kexec binary missing?), so try simply reboot(RB_KEXEC) */
++                                sleep(15);
+                                 (void) reboot(cmd);
+                                 _exit(EXIT_FAILURE);
+                         }
+@@ -614,6 +615,7 @@ int main(int argc, char *argv[]) {
+                 _fallthrough_;
+ 
+         case RB_AUTOBOOT:
++                sleep(15);
+                 (void) reboot_with_parameter(REBOOT_LOG);
+                 log_info("Rebooting.");
+                 break;
+@@ -630,6 +632,7 @@ int main(int argc, char *argv[]) {
+                 assert_not_reached();
+         }
+ 
++        sleep(15);
+         (void) reboot(cmd);
+         if (errno == EPERM && in_container) {
+                 /* If we are in a container, and we lacked

pkgs/systemd/default.nix

@@ -0,0 +1,9 @@
+{ pkgs }:
+
+(pkgs.systemd.overrideAttrs (upstream: {
+  patches = (upstream.patches or []) ++ [
+    # give the HDD time to spin down before abruptly cutting power
+    ./01-spindown-drive.patch
+  ];
+}))
+