It seems these tracing messages are outputted by the kde-open5 utility. I do not think we should hide at xdg-utils level any messages from underlying tools. However, you may redirect unneeded output on your own.
$ xdg-open readme.pdf >/dev/null ** Changed in: xdg-utils (Ubuntu) Status: New => Opinion -- You received this bug notification because you are a member of Desktop Packages, which is subscribed to xdg-utils in Ubuntu. https://bugs.launchpad.net/bugs/849413 Title: xdg-open spitting out debug messages on start Status in xdg-utils package in Ubuntu: Opinion Bug description: $ xdg-open readme.pdf <unknown program name>(5811)/ ClientApp::doIt: Creating ClientApp kioclient(5811) ClientApp::kde_open: KUrl("file:///home/testuser/readme.pdf") $ xdg-open --version xdg-open 1.0.1 $ uname -a Linux 2.6.32-33-generic #72-Ubuntu SMP Fri Jul 29 21:08:37 UTC 2011 i686 GNU/Linux $ cat /etc/issue Ubuntu 10.04.3 LTS \n \l $ To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/xdg-utils/+bug/849413/+subscriptions -- Mailing list: https://launchpad.net/~desktop-packages Post to : desktop-packages@lists.launchpad.net Unsubscribe : https://launchpad.net/~desktop-packages More help : https://help.launchpad.net/ListHelp