Add comment describing expected issue on modern GNU/Linux

diff --git a/gatekeeper.pl b/gatekeeper.pl
index c9527880a49178f770bc53b514fa25d11c1a5970..4fe6fb74dc6faa18c8d08f1fec8558f16e212045 100755 (executable)
--- a/gatekeeper.pl
+++ b/gatekeeper.pl
@@ -935,6 +935,9 @@ sub scan_incoming {
   # If neither of those 2 conditions are met, the lsof call will not see
   # the open files because they are owned by another user.
   # On modern (Debian) systems, condition a) is not met.
+  # On modern GNU/Linux systems, unless either condition b) is met or lsof
+  # is installed setuid root, the kernel will not permit the open files to
+  # be seen because they are owned by another user.
   my @lsof_args = (LSOF_BIN, "-Fn",
        map { File::Spec->catfile($directory, $_) } keys %possible);
   ftp_syslog('debug', "DEBUG: lsof command line: " . join(' ',@lsof_args))