Comment 7 for bug 269915

The systray applet should not be started if the hplip-gui package (this one requires python-qt3) is not installed. The autostarter file for the systray applet, /etc/xdg/autostart/hplip-systray.desktop, is in hplip-gui. Also menu entries for GUI apps, like hp-ttolbox are only in hplip-gui.

Tools run in text mode should not trigger the systray applet. Is this the case?

If the applet is triggered by a non-GUI process (does the hpfax CUPS backend trigger it when it receives a job?) then the applet should exit gracefully. putting a decent error message into an appropriate log file (like /var/log/syslog). If it crashes, it triggers the automatic bug reporter Apport in Ubuntu (and perhaps also similar things in other modern distros). The caller should also handle this case gracefully and issue a decent error message (for CUPS backends or filters drop it in /var/log/cups/error_log).