As of Natty you can not. Is was dropped due to flaws that could not be addressed and because hibernation/suspend actually does this better.
From the announcement:
Hey fellow desktop lovers,
Here is a notice on what we decided during the Rally: we drop session
saving from natty in Ubuntu. The disablement is already effective in
What was the option about?
The option was about launching on session start, the applications
which were running when you close your session, and getting them in
the exact same state than when they were closed.
It was available through gnome-session-properties in a dedicated tab.
It was possible to choose there to save right now all opened
applications or to do that everytime on session close.
Why removing it?
We saw a lot of side effects during the previous cycles when we
started to use multiples session (like in UNE, desktop session and
- the saved applications contains the list of all running application, including the window manager, the panel and such… Consequently, we got
a lot of patches and hack to avoid saving mutter, compiz, metacity,
and the panels in lucid and maverick, so that when someone wanted to
start a session, the required components from the session will indeed
been launched instead of the saved one.
We tried last week to change the desktop order but it went quite wrong with a lot of settings and we had to revert it.
In addition to that, session saving never really worked with all the default applications we have (for instance, openoffice, firefox…) and
even with supported applications like gedit: the opened documents
weren't started again, making the feature quite useless.
As there is no strong intend to solve that in the short term and we
need to focus on other parts of the desktop area first, we decided
than instead of shipping a broken feature (there was already a lot of
side effects people using this feature encountered that cycle, and
time to debug it, to find it was coming from a saved session was quite
expensive…) to unable it for natty. With that, it will enable us to
ensure a first class experience in natty on the ubuntu desktop,
without getting a lot of upgrade failures and people rebooting getting
a blank background.
I still personally think that this feature can be really good addition
to Ubuntu default experience if we can take time to make it very
polished as well as working for most of - if not all - major
applications (at least, all applications by default on the CD). If
someone wants to jump in this hard and long task, he's more than
welcome to discuss it either on this mailing list or in the #ubuntu-desktop channel on freenode.
Thanks for your attention,