diff --git a/BUILD_DEPLOY.md b/BUILD_DEPLOY.md
index c9b15ff..9e79b8a 100644
--- a/BUILD_DEPLOY.md
+++ b/BUILD_DEPLOY.md
@@ -137,3 +137,5 @@ chmod -R 775 .../out .../ota-artifacts
 Apply nginx OTA block: `nginx.apps-port80.fragment` (`location ^~ /v0/ota/`), then `nginx -t && rc-service nginx reload` on BE.
 
 If **Start build** shows *Network error*, check BE `php-fpm81` log: often `mkdir(): Permission denied` on `out/builds` (HTTP 500, not a browser network fault).
+
+If the build log shows **`mkdir /.docker: permission denied`**, PHP-FPM is running as `nobody` with `HOME=/`. Set `build.docker_home` (default `/var/www/ac/broadcast`) and run `prepare-be-builder-dirs.sh` so `/.docker` is not used. Ensure `nobody` is in group `docker`.