I try to execute a java application at startup in a yocto based linux device. I added a script at
update-rc.d etic defaults
Well, often such issues are due to a different environment when executing the start script by hand, as compared to when it's being run from the init system. For instance, your
.bashrc won't have been sourced, when running from the init system.
You can use eg
logger to easily log things from your init-script, and this rather easily find out what goes wrong.