The systemd notification system uses sockets. See https://www.freedesktop.org/software/systemd/man/sd_notify.html https://www.freedesktop.org/software/systemd/m

The systemd notification system uses sockets. See https://www.freedesktop.org/software/systemd/man/sd_notify.html https://www.freedesktop.org/software/systemd/man/sd_notify.h... It looks like it has grown a bit since the last time I saw the manpage...