Adding more info - System Ubuntu Xenial 16.04.2 4.4.0-72-generic. using gdm3 and Unity session. It appears the cause of the failure reported in syslog is not clear and not related to 'df' command failure; except that the history in syslog showed GLib-GObject-CRITICAL errors, with no other erroneous application level observation prior to df failure.
Adding more info - System Ubuntu Xenial 16.04.2 4.4.0-72-generic. using gdm3 and Unity session. It appears the cause of the failure reported in syslog is not clear and not related to 'df' command failure; except that the history in syslog showed GLib-GObject- CRITICAL errors, with no other erroneous application level observation prior to df failure.