Tries to address #7463

- run the remote `bridge` command in a login shell, to make sure PATH is
  properly defined
- add `set -o pipefail` to ensure that errors are properly propagated
  back through the remote SSH command

perl-xCAT/xCAT/MacMap.pm

@@ -723,7 +723,7 @@ sub refresh_switch {
         my $mymac;
         my $myport;
 
-        my @res=xCAT::Utils->runcmd("ssh -o StrictHostKeyChecking=no -o PasswordAuthentication=no $switch 'bridge fdb show|grep -i -v permanent|tr A-Z a-z  2>/dev/null' 2>/dev/null",-1);
+        my @res=xCAT::Utils->runcmd("ssh -o StrictHostKeyChecking=no -o PasswordAuthentication=no $switch \"bash -lc 'set -o pipefail; bridge fdb show |grep -i -v permanent |tr A-Z a-z  2>/dev/null'\" 2>/dev/null",-1);
         if ($::RUNCMD_RC) {
             xCAT::MsgUtils->message("S", "Failed to get mac table with ssh to $switch, fall back to snmp! To obtain mac table with ssh, please make sure the passwordless root ssh to $switch is available");
             if ($self->{collect_mac_info}) {
@@ -774,6 +774,7 @@ sub refresh_switch {
         }
     }
 
+
     my $session = $self->getsnmpsession('community' => $community, 'switch' => $switch);
     unless ($session) {
         xCAT::MsgUtils->message("S", "Failed to communicate with $switch");