systemd is a Linux initialization system and service manager that includes features like on-demand starting of daemons, mount and automount point maintenance, snapshot support, and processes tracking using Linux control groups.

What is the use of systemd in Linux?

Systemd provides a standard process for controlling what programs run when a Linux system boots up. While systemd is compatible with SysV and Linux Standard Base (LSB) init scripts, systemd is meant to be a drop-in replacement for these older ways of getting a Linux system running.

Why is Systemd bad?

The init program runs as root and is always running, so if there is a bug in the init system it has the potential to be very nasty. Many Linux distros are running systemd so if there is a bug in it, they all will have security issues. Systemd is very complex increasing the probability of it having a bug.