Master Linux Startup: rc.local, init.d, and systemd Explained

In Linux there are several ways to run scripts after the system boots. Below are the most common methods.

/etc/rc.local

/etc/rc.local

is the traditional init script used before systemd. It is a shell script executed at the end of the boot process with root privileges, allowing custom commands or services.

It provides a simple way to customize the system or start background processes.

With the adoption of systemd, many distributions have deprecated /etc/rc.local in favor of systemd’s native mechanisms.

/etc/init.d/

/etc/init.d/

is a directory that historically stored SysVinit scripts, which are shell scripts for starting, stopping, or managing services.

SysVinit uses runlevels; scripts placed in /etc/init.d/ correspond to these levels, e.g., /etc/init.d/apache2 manages the Apache web server.

Although some legacy distributions still use SysVinit for compatibility, most modern Linux distributions default to systemd.

systemd

systemd is a modern init system and service manager that has replaced SysVinit in many Linux distributions, offering parallel service startup, socket activation, logging, and dependency tracking.

Instead of separate init scripts, systemd uses unit files (declarative configuration) stored in /usr/lib/systemd/system/ or /etc/systemd/system/ with a .service extension.

systemd also introduces “targets” as replacements for runlevels, grouping units to define overall system states such as multi-user.target or graphical.target.

Overall, systemd provides improved service management, faster parallel startup, better logging, and a simpler initialization approach compared to traditional init systems.