It's been several days now that I am searching for what goes wrong.
The problem is :
PCManFM is the one that starts background and icons, through the /home/user/.config/openbox/autostart.sh file (command : "pcmanfm -d &") and in live usb or live vbox it does a segmentation error, so the background stays black at first login.
I could just put tint2, feh, and then no problem : feh does not crash in any case. But the deal there is to get to also be able to provide a version that can be used in Edu project, or anywhere, with the choice, right-click menu with openbox, and menus from lxpanel, and then be able to use the right-click in lxpanel menus to put icons on desktop if the users like it this way.
All this is available now, and works fine, except in theses 2 cases : live usb and live virtualbox. probably in live cdrom too, even if I didn't try. Once logued in, right-click or go to menu to start pcmanfm: the background and the "My Documents" icon appear. Logout/login gives the same result. After install and first login, the problem disappears as well.
Now when does it work on first login ? Well, it works on first login,if the distro is started with runlevel 3
! I put init 3 on kernel command line, in Live usb, in live Virtualbox and in both cases that worked !
I thought that it had something to do with speedboot, after I read a part in rc.sysinit that showed speedboot was disabled if runlevel was else than 5, but after I put "no" to the /etc/sysconfig/speedboot file instead of "auto", the result didn't change and I ended with lxpanel and a black background.
Now I'm out of ideas to pursue the quest of the solution.
How could I fix it ?
Links to the threads where I talk about it until now:PCLinuxOS Openbox Mini - who wants to test ?New Project Ideas
Link to a Mandriva information about speedboot that conforted me in the idea it could be interesting to try to disable it:http://wiki.mandriva.com/en/2010.0_Errata#Sometimes_you_may_see_anomalies_which_may_be_caused_by_speedboot
When black and segfault: