diff --git a/xCAT-server/lib/xcat/plugins/mknb.pm b/xCAT-server/lib/xcat/plugins/mknb.pm
index 891310e2d..be6ab48fc 100644
--- a/xCAT-server/lib/xcat/plugins/mknb.pm
+++ b/xCAT-server/lib/xcat/plugins/mknb.pm
@@ -327,6 +327,41 @@ sub genesis_lzma_command {
     return;
 }
 
+#-------------------------------------------------------------------------------
+
+=head3 stage_genesis_payload
+
+Descriptions:
+    Copy the Genesis payload into place for mknb: for a legacy image the unpacked
+    root tree and then the kernel, for an exported image the nbroot tree.
+
+    Extracted so the outcome can be driven directly. The copies are the only
+    place mknb learns that an installed Genesis image is unusable, and a caller
+    cannot tell WHICH copy failed from a single exit status.
+
+Arguments:
+    genesis_type, genesis_dir, tftpdir, arch, tempdir, and an optional run
+    coderef used in place of system() by the tests.
+Returns:
+    (rc, source) -- rc is the exit status of the copy that failed, and source
+    names it, so the caller reports the file it could not read.
+
+=cut
+
+#-------------------------------------------------------------------------------
+sub stage_genesis_payload {
+    my (%a)  = @_;
+    my $run  = $a{run} || sub { return system($_[0]); };
+    my $rc;
+    if (($a{genesis_type} // '') eq 'legacy') {
+        $rc = $run->("shopt -s dotglob; GLOBIGNORE=\".:..\" cp -a $a{genesis_dir}/fs/* $a{tempdir}");
+        $rc = $run->("cp -a $a{genesis_dir}/kernel $a{tftpdir}/xcat/genesis.kernel.$a{arch}");
+        return ($rc, "$a{genesis_dir}/fs");
+    }
+    $rc = $run->("cp -a $a{genesis_dir}/nbroot/* $a{tempdir}");
+    return ($rc, "$a{genesis_dir}/nbroot");
+}
+
 sub process_request {
     my $request  = shift;
     my $callback = shift;
@@ -555,21 +590,13 @@ sub process_request {
     unless (-e "$tftpdir/xcat") {
         mkpath("$tftpdir/xcat");
     }
-    my $rc;
-    if ($genesis_type eq 'legacy') {
-        $rc = system("shopt -s dotglob; GLOBIGNORE=\".:..\" cp -a $genesis_dir/fs/* $tempdir");
-        $rc = system("cp -a $genesis_dir/kernel $tftpdir/xcat/genesis.kernel.$arch");
-        $invisibletouch = 1;
-    } else {
-        $rc = system("cp -a $genesis_dir/nbroot/* $tempdir");
-    }
+    $invisibletouch = 1 if $genesis_type eq 'legacy';
+    my ($rc, $failed_src) = stage_genesis_payload(
+        genesis_type => $genesis_type, genesis_dir => $genesis_dir,
+        tftpdir => $tftpdir, arch => $arch, tempdir => $tempdir);
     if ($rc) {
         system("rm -rf $tempdir");
-        if ($invisibletouch) {
-            $callback->({ error => ["Failed to copy $genesis_dir/fs contents"], errorcode => [1] });
-        } else {
-            $callback->({ error => ["Failed to copy $genesis_dir/nbroot contents"], errorcode => [1] });
-        }
+        $callback->({ error => ["Failed to copy $failed_src contents"], errorcode => [1] });
         return;
     }
     my $sshdir;
diff --git a/xCAT-test/unit/mknb_genesis_staging.t b/xCAT-test/unit/mknb_genesis_staging.t
new file mode 100644
index 000000000..262401f41
--- /dev/null
+++ b/xCAT-test/unit/mknb_genesis_staging.t
@@ -0,0 +1,64 @@
+#!/usr/bin/env perl
+# mknb stages the Genesis payload before it can build a netboot image. Those copies are the
+# only point at which mknb learns that an installed Genesis image is unusable, so a copy that
+# fails silently produces an initramfs built from nothing and an exit status of 0 -- the node
+# then never boots, with no error anywhere naming the cause.
+use strict;
+use warnings;
+
+use FindBin;
+use lib "$FindBin::Bin/../../perl-xCAT";
+use lib "$FindBin::Bin/../../xCAT-server/lib/perl";
+use Test::More;
+
+BEGIN { $INC{'xCAT/Utils.pm'} = 1; $INC{'xCAT/MsgUtils.pm'} = 1;
+        $INC{'xCAT/Table.pm'} = 1; $INC{'xCAT/NetworkUtils.pm'} = 1;
+        $INC{'xCAT/TableUtils.pm'} = 1; $INC{'xCAT_monitoring/monitorctrl.pm'} = 1; }
+
+require "$FindBin::Bin/../../xCAT-server/lib/xcat/plugins/mknb.pm";
+
+can_ok('xCAT_plugin::mknb', 'stage_genesis_payload')
+    or BAIL_OUT('mknb has no stage_genesis_payload to drive');
+
+# Drive the routine with a runner that fails exactly one copy, so each assertion names the
+# copy it is about rather than the pair.
+sub stage {
+    my (%opt) = @_;
+    my @ran;
+    my ($rc, $src) = xCAT_plugin::mknb::stage_genesis_payload(
+        genesis_type => $opt{type} // 'legacy',
+        genesis_dir  => '/opt/xcat/share/xcat/netboot/genesis/x86_64',
+        tftpdir      => '/tftpboot',
+        arch         => 'x86_64',
+        tempdir      => '/tmp/scratch',
+        run          => sub {
+            my ($cmd) = @_;
+            push @ran, $cmd;
+            return ($opt{fail} && $cmd =~ /$opt{fail}/) ? 256 : 0;
+        },
+    );
+    return { rc => $rc, src => $src, ran => \@ran };
+}
+
+# --- legacy: both copies must be able to fail the step -----------------------
+my $ok = stage();
+is($ok->{rc}, 0, 'a legacy image whose copies both succeed stages cleanly');
+is(scalar @{ $ok->{ran} }, 2, 'the legacy path copies the root tree and the kernel');
+
+my $nofs = stage(fail => qr{/fs/\*});
+isnt($nofs->{rc}, 0, 'an unreadable root tree fails the step');
+like($nofs->{src}, qr{/fs$}, 'and the failure names the root tree');
+
+my $nokernel = stage(fail => qr{/kernel });
+isnt($nokernel->{rc}, 0, 'a missing kernel fails the step');
+like($nokernel->{src}, qr{/kernel$}, 'and the failure names the kernel, not the root tree');
+
+# --- exported (OpenEmbedded) path -------------------------------------------
+my $nonb = stage(type => 'exported', fail => qr{/nbroot/\*});
+isnt($nonb->{rc}, 0, 'an unreadable nbroot fails the step');
+like($nonb->{src}, qr{/nbroot$}, 'and the failure names nbroot');
+
+my $oknb = stage(type => 'exported');
+is($oknb->{rc}, 0, 'an exported image whose copy succeeds stages cleanly');
+
+done_testing();