box: Only use systemd-pty-forward if stdout is connected to tty

Otherwise piping mkosi box output to less will hang on exit.

diff --git a/mkosi/__init__.py b/mkosi/__init__.py
index e760e928511b43c598285f396dc2385939c95576..d6636995643e5a4ee2653a15bafecd4b053844a2 100644 (file)
--- a/mkosi/__init__.py
+++ b/mkosi/__init__.py
@@ -4195,7 +4195,7 @@ def run_box(args: Args, config: Config) -> None:
 
     cmdline = [*args.cmdline]
 
-    if sys.stdin.isatty() and config.find_binary("systemd-pty-forward"):
+    if sys.stdin.isatty() and sys.stdout.isatty() and config.find_binary("systemd-pty-forward"):
         cmdline = [
             "systemd-pty-forward",
             "--title=mkosi-sandbox",