SysVinit – Difference Between /etc/rc.d/rc.d and /etc/rc.d

Architecturedirectory-structureinit-scriptinit.dsysvinit

I know that rc*.d directories are used at startup, or reboot, or so on time, for starting or stopping programs. Can anybody explain me what's the difference between the rc*.d folders placed under the /etc/ path and the other placed under the /etc/rc.d/ path.

Also, what's the difference between /etc/init.d and /etc/rc.d/init.d?

Thanks.

N.B. I'm running CentOS 6.2.

Best Answer

Nothing. Different Linux distributions, and the LSB, had different standards, so both are present on CentOS to make it easier to run software from different versions. One is just a symbolic link to the other.

http://www.centos.org/docs/5/html/5.1/Installation_Guide/s2-boot-init-shutdown-init.html gives details on the boot process, but ultimately all the init scripts are almost-but-not-completely identical on the different Linux systems.

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directory-structure – How Linux File System Organization Differs from Windows

Have a look at the Filesystem Hierarchy Standard (FHS), which is a standard of organising directory structure. I strongly suspect most (all?) Linux-based systems more or less follow it.

Linux – Connection Between /etc/init.d and /etc/rcX.d Directories

Let's forget init.d or rcx.d and keep things very simple. Imagine you were programming a program whose sole responsibility is to run or kill other scripts one by one.

However your next problem is to make sure they run in order. How would you perform that?

And lets imagine this program looked inside a scripts folder for running the scripts. To order the priority of scripts you would name them in lets say numerical order. This order is what dictates the relation between init.d and rc

In other words init.d contains the scripts to run and the rcX.d contains their order to run.

The X value in rcX.d is the run level. This could be loosely translated to the OS current state.

If you dig inside the rcX.d scripts you will find this formatting:

Xxxabcd

X is replaced with K or S, which stands for whether the script should be killed or started in the current run level
xx is the order number
abcd is the script name (the name is irrelevant however where it points is the script this will run)

Best Answer

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