diff --git a/perl-xCAT/xCAT/DHCP/Backend.pm b/perl-xCAT/xCAT/DHCP/Backend.pm
index 1a3fcd42a..74d1c6f74 100644
--- a/perl-xCAT/xCAT/DHCP/Backend.pm
+++ b/perl-xCAT/xCAT/DHCP/Backend.pm
@@ -16,7 +16,7 @@ sub normalize {
     return;
 }
 
-sub select {
+sub choose {
     my ( $class, %args ) = @_;
 
     my $requested = exists $args{requested} ? $args{requested} : $class->_site_backend();
@@ -89,12 +89,16 @@ sub backend_class {
 sub new_backend {
     my ( $class, %args ) = @_;
 
-    my $selection = $class->select(%args);
+    my $selection = $class->choose(%args);
     return $selection if $selection->{error};
 
     my $backend_class = $class->backend_class( $selection->{name} );
-    eval "require $backend_class";
-    if ($@) {
+    ( my $backend_file = "$backend_class.pm" ) =~ s{::}{/}g;
+    my $loaded = eval {
+        require $backend_file;
+        1;
+    };
+    if (!$loaded) {
         return {
             %$selection,
             error => "Unable to load DHCP backend '$selection->{name}': $@",
@@ -105,19 +109,23 @@ sub new_backend {
 }
 
 sub _site_backend {
-    eval {
+    my $backend = eval {
         require xCAT::TableUtils;
         return xCAT::TableUtils->get_site_attribute('dhcpbackend', 'auto');
-    } || 'auto';
+    };
+
+    return $backend || 'auto';
 }
 
 sub _osver {
     my ( $class, $type ) = @_;
 
-    eval {
+    my $osver = eval {
         require xCAT::Utils;
         return defined($type) ? xCAT::Utils->osver($type) : xCAT::Utils->osver();
-    } || 'unknown';
+    };
+
+    return $osver || 'unknown';
 }
 
 sub _command_exists {
diff --git a/perl-xCAT/xCAT/DHCP/Backend/Kea.pm b/perl-xCAT/xCAT/DHCP/Backend/Kea.pm
index ea3010af7..24d26dee0 100644
--- a/perl-xCAT/xCAT/DHCP/Backend/Kea.pm
+++ b/perl-xCAT/xCAT/DHCP/Backend/Kea.pm
@@ -707,7 +707,8 @@ sub _control_agent_not_found {
 }
 
 sub _first_defined {
-    foreach my $value (@_) {
+    my @values = @_;
+    foreach my $value (@values) {
         return $value if defined $value;
     }
 
diff --git a/xCAT-server/share/xcat/tools/dhcpop b/xCAT-server/share/xcat/tools/dhcpop
index 79d06316a..a9b55cb03 100755
--- a/xCAT-server/share/xcat/tools/dhcpop
+++ b/xCAT-server/share/xcat/tools/dhcpop
@@ -1,5 +1,8 @@
 #!/usr/bin/perl -w
 #use Data::Dumper;
+use strict;
+use warnings;
+
 BEGIN
 {
     $::XCATROOT = $ENV{'XCATROOT'} ? $ENV{'XCATROOT'} : '/opt/xcat';
@@ -101,7 +104,8 @@ if($help){
     }
 
     my $omshell;
-    open($omshell, "|/usr/bin/omshell >/dev/null");
+    open($omshell, '|-', '/bin/sh', '-c', '/usr/bin/omshell >/dev/null')
+      or die "Unable to start omshell: $!";
     print $omshell "key "
       . $id . " \""
       . $passwd . "\"\n";
diff --git a/xCAT-test/unit/dhcp_backend_selection.t b/xCAT-test/unit/dhcp_backend_selection.t
index b674b7085..85e07991c 100644
--- a/xCAT-test/unit/dhcp_backend_selection.t
+++ b/xCAT-test/unit/dhcp_backend_selection.t
@@ -50,43 +50,43 @@ is(
 );
 
 is(
-    xCAT::DHCP::Backend->select( requested => 'isc', os => 'rhel10', platform => 'el10' )->{name},
+    xCAT::DHCP::Backend->choose( requested => 'isc', os => 'rhel10', platform => 'el10' )->{name},
     'isc',
     'explicit ISC override wins on EL10'
 );
 
 is(
-    xCAT::DHCP::Backend->select( requested => 'kea', os => 'rhel9', platform => 'el9' )->{name},
+    xCAT::DHCP::Backend->choose( requested => 'kea', os => 'rhel9', platform => 'el9' )->{name},
     'kea',
     'explicit Kea override wins on EL9'
 );
 
 is(
-    xCAT::DHCP::Backend->select( requested => 'auto', os => 'rhel9', platform => 'el9' )->{name},
+    xCAT::DHCP::Backend->choose( requested => 'auto', os => 'rhel9', platform => 'el9' )->{name},
     'isc',
     'auto selects ISC on EL9'
 );
 
 is(
-    xCAT::DHCP::Backend->select( requested => 'auto', os => 'rhel10', platform => 'el10' )->{name},
+    xCAT::DHCP::Backend->choose( requested => 'auto', os => 'rhel10', platform => 'el10' )->{name},
     'kea',
     'auto selects Kea on EL10'
 );
 
 is(
-    xCAT::DHCP::Backend->select( requested => 'auto', os => 'ubuntu24.04', os_name => 'ubuntu', version => '24.04' )->{name},
+    xCAT::DHCP::Backend->choose( requested => 'auto', os => 'ubuntu24.04', os_name => 'ubuntu', version => '24.04' )->{name},
     'kea',
     'auto selects Kea on Ubuntu 24.04'
 );
 
 like(
-    xCAT::DHCP::Backend->select( requested => 'invalid' )->{error},
+    xCAT::DHCP::Backend->choose( requested => 'invalid' )->{error},
     qr/Invalid site\.dhcpbackend/,
     'invalid explicit backend returns a clear error'
 );
 
 like(
-    xCAT::DHCP::Backend->select(
+    xCAT::DHCP::Backend->choose(
         requested       => 'kea',
         check_available => 1,
         available       => { kea => 0 },
@@ -96,7 +96,7 @@ like(
 );
 
 is(
-    xCAT::DHCP::Backend->select(
+    xCAT::DHCP::Backend->choose(
         requested       => 'kea',
         check_available => 1,
         available       => { kea => 1 },
diff --git a/xCAT-test/unit/dhcp_kea_config_validation.t b/xCAT-test/unit/dhcp_kea_config_validation.t
index ccdff0b61..633d7acb1 100644
--- a/xCAT-test/unit/dhcp_kea_config_validation.t
+++ b/xCAT-test/unit/dhcp_kea_config_validation.t
@@ -202,7 +202,9 @@ sub validation_temp_dir {
     my $command = shell_quote($kea_dhcp4) . ' -t ' . shell_quote($path) . ' 2>&1';
     my $output = `$command`;
     unlink $path;
-    return undef if $output =~ /Unable to open file/;
+    if ( $output =~ /Unable to open file/ ) {
+        return;
+    }
 
     return '';
 }
diff --git a/xCAT-test/unit/dhcp_kea_control_agent_smoke.t b/xCAT-test/unit/dhcp_kea_control_agent_smoke.t
index 194b260ee..f7061a6e2 100644
--- a/xCAT-test/unit/dhcp_kea_control_agent_smoke.t
+++ b/xCAT-test/unit/dhcp_kea_control_agent_smoke.t
@@ -137,6 +137,8 @@ sub write_file {
     open(my $fh, '>', $path) or die "Unable to write $path: $!";
     print $fh $content;
     close($fh) or die "Unable to close $path: $!";
+
+    return 1;
 }
 
 sub start_daemon {
diff --git a/xCAT-test/unit/dhcp_kea_renderer.t b/xCAT-test/unit/dhcp_kea_renderer.t
index b6084dab6..75f76f153 100644
--- a/xCAT-test/unit/dhcp_kea_renderer.t
+++ b/xCAT-test/unit/dhcp_kea_renderer.t
@@ -186,8 +186,8 @@ close($configfh);
 my $write_result = $backend->write_dhcp4_json('{"new":true}', path => $config_path, skip_validate => 1, backup_existing => 1);
 ok( !$write_result->{error}, 'write_dhcp4_json succeeds with backup_existing' );
 is( $write_result->{backup}, "$config_path.xcatbak", 'backup path is reported' );
-my $config_mode = ( stat($config_path) )[2] & 07777;
-ok( $config_mode == 0640 || $config_mode == 0644, 'written config is readable by the Kea service user' );
+my $config_mode = ( stat($config_path) )[2] & oct('7777');
+ok( $config_mode == oct('640') || $config_mode == oct('644'), 'written config is readable by the Kea service user' );
 open(my $backupfh, '<', "$config_path.xcatbak") or die "Unable to read backup config: $!";
 my $backup_content = <$backupfh>;
 close($backupfh);