/etc/rc[0-6].d Directory: Explanation & Insights

Contains scripts for different runlevels

The /etc/rc[0-6].d directories are system directories that contain scripts used to start or stop system services. These directories are used during the system boot process and each one corresponds to a different runlevel. The scripts within these directories are not placed there directly but are usually symbolic links pointing to the init scripts located in the /etc/init.d directory.

What It Is Used For

These directories play a crucial role in the initialization of your Linux system. They are responsible for starting and stopping services based on the runlevel your system is entering or leaving. For example, the scripts in /etc/rc0.d are run when the system is halted, while those in /etc/rc6.d are run when the system is rebooting.

Why It Is Important

Understanding the role of these directories is essential for managing your Linux system, especially if you are setting up a server. The scripts in these directories control essential services like networking, logging, and scheduling. If a service fails to start properly, it may be due to a problem with the corresponding script in one of these directories.

How It May Be Related To Other Directories/Commands/Files

As mentioned earlier, the scripts in these directories are usually symbolic links to the actual init scripts in the /etc/init.d directory. This means that changes to the scripts in /etc/init.d will affect the operation of the corresponding services.

It's also worth noting that the operation of these directories is controlled by the init command, which is the first process started by the Linux Kernel during system boot.

Potential Problems And Pitfalls

One common problem related to these directories is the incorrect configuration of service start and stop priorities. Each script in these directories is prefixed with a number, which determines the order in which the scripts are run. If these numbers are not configured correctly, services may fail to start due to dependencies on other services that have not yet started.

For example, to view the contents of the /etc/rc5.d directory, you can use the ls command:

ls /etc/rc5.d

This will give you an output similar to:

S01acpid  S01atop      S01autofs            S01cron  S01lvm2-lvmpolld  S01named              S01ntp    S01rsyslog        S01ssh   S01uuidd
S01atd    S01atopacct  S01console-setup.sh  S01dbus  S01mdadm          S01nfs-kernel-server  S01rsync  S01smartmontools  S01sudo

Examples In Bash

To start or stop a service, you could in principle run the corresponding script.

However, it’s usually better to use the service or systemctl command to manage services, as these commands provide a more standardized interface and handle dependencies between services. For example, you can stop the network service with the following command:

systemctl stop network

In conclusion, the /etc/rc[0-6].d directories are essential components of the Linux system boot process. By understanding their role and how to work with them, you can gain greater control over your Linux system and solve common problems related to system services.