The SYSLINUX configuration on Ubuntu Live CD is somewhat confusing, but I had figured out by reading this post on Unix.SE and refer to this Syslinux Wiki.
Part A: Skip install/Boot to desktop
To boot directly to Live session, you need to do two things:
replace the default vesamenu.c32
with default live
(whose label live
is found in /isolinux/txt.cfg
file)
comment the last line ui gfxboot bootlogo
using #
at beginning of line
Step 2 is required, otherwise the initial splash screen will still be visible until timeout. This is due to ui
module will override the default
setting, as explained in this subtopic on the Wiki:
Therefore, if UI is used, the PROMPT directive is ignored and the UI command -- not the DEFAULT command -- is automatically launched
Default /isolinux/isolinux.cfg
# D-I config version 2.0
include menu.cfg
default vesamenu.c32
prompt 0
timeout 50
ui gfxboot bootlogo
Modified /isolinux/isolinux.cfg
# D-I config version 2.0
include menu.cfg
default live
prompt 0
timeout 50
#ui gfxboot bootlogo
I have tested the modified configuration using Xubuntu 14.04 ISO image, but the same steps should apply to other Ubuntu and official derivatives.
Part B: Run custom app
As for launching the application, it should be doable by adding the path of target executable to the "startup" menu or something similar. For example, on Xfce Desktop Environment, it is found at Settings Manager > Session and Startup > Application Autostart.
Above all, my answer is more toward the solution for "Skip install/Boot to desktop". The latter part "Run custom app" shouldn't be an issue for most users.