systemd is one of several PID 1 implementations.

System unit locations:

• /etc/systemd/system/ → units installed by the system administrator
• /usr/lib/systemd/system/ → units provided by installed packages

User unit locations:

• ~/.config/systemd/user/ where the user puts their own units.
• /etc/systemd/user/ where system-wide user units are placed by the system administrator.
• ~/.local/share/systemd/user/ where units of packages that have been installed in the home directory belong.
• /usr/lib/systemd/user/ where units provided by installed packages belong

Back in the days, superdaemons listened on all sockets and started up the needed services on request. Nowadays, the most common implementation is systemd's socket activation paired with the corresponding service unit file.

See https://0pointer.net/blog/projects/inetd.html for more info on this.

systemd has journald.

Make logging nonpersistent with Storage=auto in /etc/systemd/journald.conf