diff --git a/Create-DevTerm-A06-OS-image-from-scratch.md b/Create-DevTerm-A06-OS-image-from-scratch.md
index 9a5c25d..295bad9 100644
--- a/Create-DevTerm-A06-OS-image-from-scratch.md
+++ b/Create-DevTerm-A06-OS-image-from-scratch.md
@@ -132,6 +132,14 @@ cd -
 sudo umount /mnt/p1
 ```
 
+umount may failed at /mnt/p1/dev  
+just use `ps aux | grep cupsd` to see if there a process named like `/usr/bin/qemu-aarch64-static /usr/sbin/cupsd -C /etc/cups/cupsd.conf -s /etc/cups/cups-files.conf`  
+
+find the pid ,use `sudo kill -9 ${pid}` with that pid  
+then umount again   
+
+
+
 # Flash the image to SD card
 * Linux  
 `sudo dd if=Armbian_21.08.0-trunk_Clockworkpi-a06_focal_current_5.10.55_xfce_desktop.img  of=/dev/sdX bs=8M status=progress`