From 43438277d8dc7243fd2e64ca984c6061dd742e72 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Dav=C3=AD=C3=B0=20Steinn=20Geirsson?= <david@dsg.is>
Date: Sat, 21 Mar 2026 20:10:06 +0000
Subject: [PATCH] fix: use screen -dmS with Type=forking for console drain
 service

screen -dmS forks to background (daemon mode), which should work
without a controlling terminal. Type=forking tells systemd to expect
the fork.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
---
 README.md            |  2 +-
 modules/scripts.nix  | 10 +++++-----
 modules/services.nix | 10 +++++-----
 3 files changed, 11 insertions(+), 11 deletions(-)

diff --git a/README.md b/README.md
index 8d100bc..1981c91 100644
--- a/README.md
+++ b/README.md
@@ -540,7 +540,7 @@ vm-shell --ssh <name>        # SSH into VM as user
 vm-shell --ssh --root <name> # SSH into VM as root
 ```
 
-The default serial console mode connects via a `tmux` session. Press `Ctrl+B, D` to detach. No configuration required.
+The default serial console mode connects via a `screen` session. Press `Ctrl+A, D` to detach. No configuration required.
 
 SSH mode requires SSH keys configured in per-VM `guestConfig` (see Advanced Configuration). For cloud-hypervisor VMs, `--ssh` automatically connects via a ProxyCommand over the vsock socket — no IP routing required.
 
diff --git a/modules/scripts.nix b/modules/scripts.nix
index 461f2db..1e68e7a 100644
--- a/modules/scripts.nix
+++ b/modules/scripts.nix
@@ -1399,8 +1399,8 @@ let
       echo "  --ssh   Use SSH over vsock (requires SSH keys configured)" >&2
       echo "  --root  Connect as root (only with --ssh)" >&2
       echo "" >&2
-      echo "Without --ssh, connects to serial console via tmux." >&2
-      echo "Detach with Ctrl+B, D" >&2
+      echo "Without --ssh, connects to serial console via screen." >&2
+      echo "Detach with Ctrl+A, D" >&2
       exit 1
     }
 
@@ -1454,13 +1454,13 @@ let
           "${vm.name}) exec ${pkgs.openssh}/bin/ssh -o StrictHostKeyChecking=no -o UserKnownHostsFile=/dev/null -o ProxyCommand=${lib.escapeShellArg "${proxyCmd}"} \$USER_NAME@localhost ;;"
       )}
     else
-      if ! ${pkgs.tmux}/bin/tmux has-session -t vmsilo-$VM_NAME 2>/dev/null; then
+      if ! ${pkgs.screen}/bin/screen -ls vmsilo-$VM_NAME >/dev/null 2>&1; then
         echo "No console session found for $VM_NAME" >&2
         echo "Is the VM running? Use: vm-start $VM_NAME" >&2
         exit 1
       fi
-      echo "Detach with Ctrl+B, D"
-      exec ${pkgs.tmux}/bin/tmux attach -t vmsilo-$VM_NAME
+      echo "Detach with Ctrl+A, D"
+      exec ${pkgs.screen}/bin/screen -x vmsilo-$VM_NAME
     fi
   '';
 in
diff --git a/modules/services.nix b/modules/services.nix
index 68c240f..7a34e6c 100644
--- a/modules/services.nix
+++ b/modules/services.nix
@@ -472,7 +472,7 @@ in
         ) (lib.filter (vm: vm.hypervisor == "crosvm") (lib.attrValues cfg.nixosVms))
       ++
         # Console screen services (one per VM)
-        # Attaches a tmux session to the console PTY to keep the buffer drained
+        # Attaches a screen session to the console PTY to keep the buffer drained
         map (
           vm:
           let
@@ -488,7 +488,7 @@ in
                 echo "Timeout waiting for console PTY" >&2
                 exit 1
               fi
-              exec ${pkgs.tmux}/bin/tmux new-session -s vmsilo-${vm.name} -x 200 -y 50 "cat /run/vmsilo/${vm.name}/console"
+              ${pkgs.screen}/bin/screen -dmS vmsilo-${vm.name} -h 10000 /run/vmsilo/${vm.name}/console
             '';
           in
           lib.nameValuePair "vmsilo-${vm.name}-console-screen" {
@@ -499,11 +499,11 @@ in
             bindsTo = [ "vmsilo-${vm.name}-vm.service" ];
 
             serviceConfig = {
-              Type = "simple";
+              Type = "forking";
               User = cfg.user;
-              ExecStartPre = "-${pkgs.tmux}/bin/tmux kill-session -t vmsilo-${vm.name}";
+              ExecStartPre = "-${pkgs.screen}/bin/screen -S vmsilo-${vm.name} -X quit";
               ExecStart = "${screenScript}";
-              ExecStopPost = "-${pkgs.tmux}/bin/tmux kill-session -t vmsilo-${vm.name}";
+              ExecStopPost = "-${pkgs.screen}/bin/screen -S vmsilo-${vm.name} -X quit";
             };
           }
         ) (lib.attrValues cfg.nixosVms)