Getting list of startup application in linux

You did not specify your distro; however, in Ubuntu and Debian you can find these applications by running:

ls /etc/init.d

All the files in this directory are actually links to the applications and on boot the OS goes through this directory and starts them all.

/etc/init.d/

Includes Linux init scripts only.

To list all AutoStart Applications in gnome, list all files under "autostart" directories. e.g.:

find / -name "*autostart*"

ls -1 "/etc/xdg/autostart" "/home/$USER/.config/autostart" "/usr/share/gdm/autostart"  "/usr/share/gnome/autostart"

To list all systemd services:

ls -1 /lib/systemd/system/*.service /etc/systemd/system/*.service