Systemd-using Linuxes like Arch Linux does not generally support the old SysV init functions like rc.local. The support is easy to add, though.
Edit /usr/lib/systemd/system/rc-local.service
:
[Unit]
Description=/etc/rc.local compatibility
[Service]
Type=oneshot
ExecStart=/etc/rc.local
RemainAfterExit=yes
[Install]
WantedBy=multi-user.target
Enable it:
systemctl enable rc-local.service
Original source: Raymii