diff --git a/xCAT-server/share/xcat/netboot/ubuntu/genimage b/xCAT-server/share/xcat/netboot/ubuntu/genimage
index 3e490c6ce..4f7c1b7be 100755
--- a/xCAT-server/share/xcat/netboot/ubuntu/genimage
+++ b/xCAT-server/share/xcat/netboot/ubuntu/genimage
@@ -381,7 +381,7 @@ unless ($onlyinitrd) {
     my %extrapkgnames; 
 
     if (keys(%extra_hash) > 0) {
-      open ($aptconfig,">","$rootimg_dir/etc/apt/sources.list.d/genimage.apt.list");
+      open ($aptconfig,">>","$rootimg_dir/etc/apt/sources.list.d/genimage.apt.list");
       my $index=1;
       foreach $pass (sort {$a <=> $b} (keys(%extra_hash))) {
         foreach (keys(%{$extra_hash{$pass}})) {