This article links to various methods to launch scripts or applications automatically when some particular event is taking place, like system startup or shutdown, shell login or logout and so on.
You can easily start your scripts or applications as daemons, see Daemon.
systemd is the default init framework, replacing initscripts. The services which are started by systemd can be found in the subfolders of
/etc/systemd/system/. Services can be enabled using the
systemctl command. For more information about systemd and how to write autostart scripts for it, see at systemd.
runit is a mature init system which offers process supervision, parallel startup, per-user service trees, granular cgroup manipulation, flexible dependency system, and boot times that don't incur the penalty of dbus. The root-level services are symlinks in
/service with the actual service directories in
/etc/sv. See the Runit page for more information.
To autostart programs in console or upon login, you can use shell startup files/directories. Read the documentation for your shell, or its ArchWiki article, e.g. Bash#Configuration file sourcing order at startup or Zsh#Autostarting applications.
/etc/profile is sourced by all Bourne-compatible shells upon login: it sets up an environment upon login and application-specific settings by sourcing any readable
X session startup
X Desktop Group
/etc/xdg/autostart and (if gnome)
$XDG_CONFIG_HOME/autostart/ folders contain
*.desktop files, which are executed every time an X session starts, determining which programs are loaded for which desktop environment. When $XDG_CONFIG_HOME is empty/undefined, ~/.config is used. For an explanation of the desktop file standard refer to Desktop Entry Specification. For a more specific description of directories used, Desktop Application Autostart Specification.
GNOME, KDE, Xfce
KDE also has a specific folder: