Execute custom script after boot on Yocto-built linux system

Question

I want to execute a script which is present in rootfs everytime system boots to indicate successful update and reset bootloader variables.

For example, the "custom-script" script in present in /etc as:

/etc
----/init.d
-----------custom-script.sh

The first step I did is to install this script in rootfs of the linux image. I have created a recipe in my custom Yocto layer. meta-custom\recipes-support\images layer directory is as follows:

.
├── files
│   ├── custom-script.sh
└── core-image-base.bb

The core-image-base.bb is:

DESCRIPTION = "Install script to Rootfs"
SUMMARY = "Install script to Rootfs and run after boot"
LICENSE = "CLOSED"

SRC_URI = "file://custom-script.sh"

do_install_append() {
    install -d 644 ${D}${sysconfdir}/init.d
    install -m 0755 ${WORKDIR}/custom-script.sh ${D}${sysconfdir}/init.d/custom-script.sh

FILES_${PN} = "${sysconfdir}/init.d"

And in the conf/layer.conf I added IMAGE_INSTALL_append = " core-image-base".

Now I want to execute this script every time the linux system boots (afrer successfully loading rootfs). Can someone please help me to accomplish this? As per my understanding, I can use systemd services to do this and this service should be executed each time the system boots. Any help would be much appreciated.

Thanks in advance.

P.S: I am using Ubuntu 20.04 and this is my first time using systemd services in Yocto with Dunfell version.

Answer 1

In order to make your custom-script.sh execute at Boot time (every time the system boots) using init.d, your custom-script.sh should have the following format

#!/bin/bash
# description: Description comes here....

# Source function library.
. /etc/init.d/functions

start() {
    # code to start app comes here
    # insert any kernel modules prior to 
    # executing/spawning any process that depends
    # on the LKM

}

stop() {
    # code to stop app comes here 
    # example: killproc program_name
    # Kill all the process started in start() function
    # remove any LKM inserted using insmod in start()

}

case "$1" in 
    start)
       start
       ;;
    stop)
       stop
       ;;
    restart)
       stop
       start
       ;;
    status)
       # code to check status of app comes here 
       # example: status program_name
       ;;
    *)
       echo "Usage: $0 {start|stop|status|restart}"
esac

exit 0 

Then you also need to add a symbolic link to your custom-script.sh in desired run-level directory e.g. /etc/rc3.d or /etc/rc5.d etc.

To add a symbolic link you need to edit core-image-base.bb (you can use your custom *.bb file as well):

DESCRIPTION = "Install script to Rootfs"
SUMMARY = "Install script to Rootfs and run after boot"
LICENSE = "CLOSED"

SRC_URI = "file://custom-script.sh"

do_install_append() {
    install -d 644 ${D}${sysconfdir}/init.d
    install -m 0755 ${WORKDIR}/custom-script.sh ${D}${sysconfdir}/init.d/custom-script.sh
    ln -sf ../init.d/custom-script.sh ${D}${sysconfdir}/rc4.d/S99custom-script.sh
    ln -sf ../init.d/custom-script.sh ${D}${sysconfdir}/rc4.d/K99custom-script.sh
}

FILES_${PN} = "${sysconfdir}/init.d"

So, I think you are missing a symbolic link to the desired run-level directory, and maybe you need to write your custom script to have a start() and stop() functions at least.

If you are using systemd, please refer Enable systemd services using yocto