Running sync fixes this issue: https://github.com/docker/docker/issues/9547 that occurs with old version of Docker that gets installed by current Cloudlab OpenStack profile
diff --git a/containers/xos/Dockerfile.devel b/containers/xos/Dockerfile.devel
index bcd9e7f..6d1c510 100644
--- a/containers/xos/Dockerfile.devel
+++ b/containers/xos/Dockerfile.devel
@@ -7,7 +7,7 @@
 # Install XOS
 ADD xos /opt/xos
 
-RUN chmod +x /opt/xos/tools/xos-manage && \
+RUN chmod +x /opt/xos/tools/xos-manage && sync && \
     /opt/xos/tools/xos-manage genkeys
 
 EXPOSE 8000