Architecture

TLP’s actions are event-driven. There is no TLP daemon, instead TLP depends on standard system daemons to monitor the relevant events:

systemd (or an alternative init system)
udevd
elogind
NetworkManager (when tlp-rdw is installed)

The following events will cause settings to be applied:

Charger plugged/unplugged - udevd

A rule in tlp.rules calls tlp auto which applies the settings profile coresponding to the actual power source or manually forced mode.

USB device plugged in - udevd

A rule in tlp.rules calls tlp-usb-udev to activate USB autosuspend.

System startup/shutdown/reboot - systemd et al.

Depends on the init system:

Systemd

The sources provide the unit tlp.service, which calls tlp init start/stop upon system startup/shutdown. Use the TLP_WITH_SYSTEMD Makefile switch to install it.

Sysvinit

The package install process must link the provided sysvinit script tlp.init i.e. /etc/init.d/tlp to the necessary runlevels by means of the target distribution.

Other init system

In case the target distribution does support neither systemd nor sysvinit, you have to provide a script that calls tlp accordingly:

tlp init start|stop|restart|force-reload|status

The parameter after init is checked by tlp.

System suspend/resume - systemd et al.

ACPI Sleep States S0ix (Idle standby), S3 (Suspend to RAM) or S4 (Suspend to disk)

Depends on the target distribution:

Systemd

The sources provide the script tlp-sleep which calls tlp suspend or tlp resume. Use the TLP_WITH_SYSTEMD Makefile switch to install it to /lib/systemd/system-sleep/tlp.

Non-systemd

elogind: the sources provide the script tlp-sleep.elogind which calls tlp suspend or tlp resume. Use the TLP_WITH_ELOGIND Makefile switch to install it to /lib/elogind/system-sleep/49-tlp-sleep.
Else: you must provide a means to invoke tlp suspend or tlp resume (your mileage may vary).

LAN, Wi-Fi, WWAN connected/disconnected - NetworkManager

The sources provide the script tlp-rdw-nm - installed to /usr/lib/NetworkManager/dispatcher.d/99tlp-rdw-nm by make install-rdw - switching the configured radio devices.

Laptop docked/undocked - udevd

A rule in tlp-rdw.rules calls tlp-rdw-udev switching the configured radio devices.