~/.xsession-errors is only created fresh by gdm and lightdm, e. g. kdm just appends (at least last time I checked). I think I'll better ask ConsoleKit:
unix-user = '1000' realname = 'Martin Pitt' seat = 'Seat1' session-type = '' active = TRUE x11-display = ':0' x11-display-device = '/dev/tty7' display-device = '' remote-host-name = '' is-local = TRUE on-since = '2011-10-07T09:46:35.438201Z' login-session-id = '4294967295'
and take the on-since property.
~/.xsession-errors is only created fresh by gdm and lightdm, e. g. kdm just appends (at least last time I checked). I think I'll better ask ConsoleKit:
unix-user = '1000' 07T09:46: 35.438201Z'
realname = 'Martin Pitt'
seat = 'Seat1'
session-type = ''
active = TRUE
x11-display = ':0'
x11-display-device = '/dev/tty7'
display-device = ''
remote-host-name = ''
is-local = TRUE
on-since = '2011-10-
login-session-id = '4294967295'
and take the on-since property.