Add New Kernel Parameter To Custom Linux Image Generated By Yocto - linux

Question

I am experimenting with Yocto project for generating custom Linux images for my embedded devices.
I have a requirement to add a persistent custom kernel parameter to /etc/sysctl.conf of the generated image.
i.e.
kernel.core_pipe_limit = 1
/etc/sysctl.conf is generated by procps package that comes with Yocto base system (meta/recipes-extended/procps/procps/sysctl.conf). However, I believe editing the sysctl.conf in the base system is not the recommended approach.
I am using a new layer for defining my custom configurations. I hope there is a way to apply a patch to a base package via a custom layer after deploying the base layer.
How can I do this?
I am aware how to persistently change a kernel variable by updating /etc/sysctl.conf (or, preferably, /etc/sysctl.d/xxx.conf). My question is, how to generate the Linux image with the necessary update applied?

Answer 1

You can add something like this in image recipe or local.conf:
set_kernel_opt(){
mkdir -p ${IMAGE_ROOTFS}/etc/sysctl.d
echo 'kernel.core_pipe_limit = 1' > ${IMAGE_ROOTFS}/etc/sysctl.d/kernel_core_pipe_limit.conf
}
ROOTFS_POSTPROCESS_COMMAND += "set_kernel_opt;"
If you want to override /etc/sysctl.conf file, you can create a meta-custom/recipes-extended/procps/procps_%.bbappend file with:
FILESEXTRAPATHS_prepend := "${THISDIR}/files:"
Then create a folder meta-custom/recipes-extended/procps/files and copy your custom sysctl.conf file in it.
Finally you can create a meta-custom/recipe-custom/custom-config/custom-config.bb recipe with:
LICENSE = "CLOSED"
SRC_URI = " \
file://kernel_core_pipe_limit.conf \
"
PV = "1.0"
S = "${WORKDIR}"
inherit allarch
do_install() {
install -d ${D}${sysconfdir}/sysctl.d
install -m 0644 ${B}/kernel_core_pipe_limit.conf ${D}${sysconfdir}/sysctl.d/
}
do_configure[noexec] = "1"
do_compile[noexec] = "1"
And copy your kernel_core_pipe_limit.conf in meta-custom/recipe-custom/custom-config/files/

Answer 2

The answer up there are wrong in my opinion. There is already a recipe providing sysctl.conf. It is procps. What you need to do is override the default configuration with a bbappend. More about append files on the online Yocto documention
Create a procps folder, procps_%.bbappend and systctl.conf in recipes-extended in your layer such as
meta-my-layer/recipes-extended/
└── procps
├── files
│   └── sysctl.conf
└── procps_%.bbappend
procps_%.bbappend:
FILESEXTRAPATHS_prepend := "${THISDIR}/files:"`
(example of) sysctl.conf:
fs.protected_hardlinks = 1
fs.protected_symlinks = 1
In case you want to keep default configuration and append to it, you only need a do_install_append step with an echo appending your text.

Answer 3

Just create a file with .conf extension under /etc/sysctl.d.
echo 'kernel.core_pipe_limit = 1' > /etc/sysctl.d/bla_bla_change_kernel_core_pipe_limit.conf
From man sysctl:
--system
Load settings from all system configuration files. Files are
read from directories in the following list in given order
from top to bottom. Once a file of a given filename is
loaded, any file of the same name in subsequent directories is
ignored.
/run/sysctl.d/*.conf
/etc/sysctl.d/*.conf
/usr/local/lib/sysctl.d/*.conf
/usr/lib/sysctl.d/*.conf
/lib/sysctl.d/*.conf
/etc/sysctl.conf
The sysctl --system should be called on system startup. On systems with systemd this is done via systemd-sysctl.service service. Thus it should load all the /etc/sysctl.d. The syntax is the same as /etc/sysct.conf syntax files.