Build custom Alibaba Cloud Linux kernel RPM packages - Alibaba Cloud Linux

Build custom Alibaba Cloud Linux kernel RPM packages to enable or disable specific kernel features. This topic describes how to modify kernel source code and rebuild RPM packages in a Docker container on an ECS instance.

Prerequisites

An ECS instance that runs Alibaba Cloud Linux. For more information, see Create an instance with Custom Launch.

Image: Alibaba Cloud Linux 2 or Alibaba Cloud Linux 3.
Instance type: 32 vCPUs or more recommended.

Note
Kernel builds are resource-intensive. Use an instance with 32 or more vCPUs to reduce build time.

Step 1: Prepare the environment

Connect to your ECS instance.

For more information, see Log on to a Linux instance using Workbench.

Download the Docker image and start the container.

#Install Docker.
sudo yum install -y docker
#Pull a Docker image.
sudo docker pull <image_url>
#Start the Docker container.
sudo docker run -itd --net host --name alinux-build <image_url> bash
#Access the Docker container.
sudo docker exec -it alinux-build bash

Replace <image_url> with the URL for your Alibaba Cloud Linux version.

Image	Docker image URL
Alibaba Cloud Linux 2	alibaba-cloud-linux-2-registry.cn-hangzhou.cr.aliyuncs.com/alinux2/alinux2
Alibaba Cloud Linux 3	alibaba-cloud-linux-3-registry.cn-hangzhou.cr.aliyuncs.com/alinux3/alinux3

This example uses the Docker image for Alibaba Cloud Linux 3.

sudo yum install -y docker
sudo docker pull alibaba-cloud-linux-3-registry.cn-hangzhou.cr.aliyuncs.com/alinux3/alinux3
sudo docker run -itd --net host --name alinux-build alibaba-cloud-linux-3-registry.cn-hangzhou.cr.aliyuncs.com/alinux3/alinux3 bash
sudo docker exec -it alinux-build bash

Step 2: Download the source code

Download and install the source RPM package.

# Download the source code package.
yum install -y wget
wget <rpm_url>/<src.rpm_name>
# Install the source code package.
rpm -ivh <src.rpm_name>

<rpm_url> is the URL to the RPM package repository for Alibaba Cloud Linux 2 or 3.

Image	RPM package URL
Alibaba Cloud Linux 2	https://mirrors.aliyun.com/alinux/2/plus/source/SRPMS/
Alibaba Cloud Linux 3	https://mirrors.aliyun.com/alinux/3/plus/source/SRPMS/kernels/

<src.rpm_name> is the name of the source RPM package you want to modify.

This example downloads the kernel-5.10.134-13.1.al8.src.rpm package for Alibaba Cloud Linux 3.

yum install -y wget
wget https://mirrors.aliyun.com/alinux/3/plus/source/SRPMS/kernels/kernel-5.10.134-13.1.al8.src.rpm
rpm -ivh kernel-5.10.134-13.1.al8.src.rpm

The files are installed to the /root/rpmbuild directory. Run ls /root/rpmbuild to verify:

Step 3: Modify the source code

Install build dependencies.

yum install -y rpm-build yum-utils
yum-builddep -y <src.rpm_name>

Replace <src.rpm_name> with your source RPM package name. Example: kernel-5.10.134-13.1.al8.src.rpm.

yum install -y rpm-build yum-utils
yum-builddep -y kernel-5.10.134-13.1.al8.src.rpm

Extract the source package.

# Enter the source code directory.
cd /root/rpmbuild/SOURCES
# Decompress the source code package.
tar xf <Name of the compressed source code package>

In this example, <source_archive_name> is linux-5.10.134-13.1.al8.tar.xz.

cd /root/rpmbuild/SOURCES
tar xf linux-5.10.134-13.1.al8.tar.xz

Go to the extracted directory.
```
cd <Name of the decompressed source code package>
```
In this example, <extracted_source_directory_name> is linux-5.10.134-13.1.al8.
```
cd linux-5.10.134-13.1.al8
```

(Optional) Modify the configuration files.

You can modify the source code or a config file. The following steps show how to modify a config file.

List the available configuration files.

ls /root/rpmbuild/SOURCES

The /root/rpmbuild/SOURCES directory contains four config files.

config file	Description
kernel-5.10.134-aarch64.config	Arm architecture, release version.
kernel-5.10.134-aarch64-debug.config	Arm architecture, debug version. For testing only.
kernel-5.10.134-x86_64.config	x86 architecture, release version.
kernel-5.10.134-x86_64-debug.config	x86 architecture, debug version. For testing only.

Select the file that matches your architecture. You can modify both platforms if needed.

Modify the configuration file.

This example uses the kernel-5.10.134-x86_64.config file for the x86 architecture.
1. Copy the configuration file to the source directory.
```
cd /root/rpmbuild/SOURCES
cp kernel-5.10.134-x86_64.config linux-5.10.134-13.1.al8/.config
```
2. Go to the source directory.
```
cd linux-5.10.134-13.1.al8
```
3. Apply default values for any new configuration options.
```
make olddefconfig
```
4. Use make menuconfig to modify kernel options. This handles configuration dependencies automatically.
```
make menuconfig
```
  In the menuconfig interface, press / to search for options.
5. Copy the modified configuration back to overwrite the original.
```
cp .config ../kernel-5.10.134-x86_64.config
```
6. Return to the parent directory.
```
cd ..
```
Note
You can use the same method to modify the configuration file for the Arm architecture.

Update the version number in the spec file.
```
cd /root/rpmbuild/SPECS
vi kernel.spec
```
Press I to enter Insert mode. When you are finished, press Esc, type :wq, and press Enter to save and exit.

Versioning recommendations: Update the version number to distinguish your build from official releases. For example:
- Change a major version like 5.10.134-12 to 5.10.134-12.0.1.
- Change a minor version like 5.10.134-13.1 to 5.10.134-13.1.1.
This example updates the version number from 5.10.134-13.1 to 5.10.134-13.1.1.

In the file, find the %define pkgrelease %{?KREL:%{KREL}}%{?!KREL:13.1} line and update it to %define pkgrelease %{?KREL:%{KREL}}%{?!KREL:13.1.1}.

You can also describe your changes in the changelog section of the kernel.spec file.

Step 4: Rebuild the RPM packages

Recompress the modified source code.

In this example, the source directory name is linux-5.10.134-13.1.al8.
1. Go to the SOURCES directory.
```
cd /root/rpmbuild/SOURCES/
```
2. Rename the source directory.
  
  In the previous step, the version number was updated from 5.10.134-13.1 to 5.10.134-13.1.1. Therefore, rename the source directory to linux-5.10.134-13.1.1.al8.
```
mv linux-5.10.134-13.1.al8 linux-5.10.134-13.1.1.al8
```
3. Recompress the directory into a tarball.
```
tar cJf linux-5.10.134-13.1.1.al8.tar.xz linux-5.10.134-13.1.1.al8
```
4. Remove the original source directory and the old tarball.
```
rm -rf linux-5.10.134-13.1.al8
rm -f linux-5.10.134-13.1.al8.tar.xz
```
Rebuild the source RPM package.
```
cd /root
rpmbuild -bs rpmbuild/SPECS/kernel.spec
```
The output shows the rebuilt package location: /root/rpmbuild/SRPMS/kernel-5.10.134-13.1.1.al8.src.rpm.
(Optional) Downgrade the dwarves package.

If your installed source RPM kernel version is 5.10.134-13.1.al8 or earlier, the build requires dwarves-1.22-1.al8 to prevent errors.
```
yum downgrade dwarves-1.22-1.al8 -y
```
Rebuild the RPM packages.
```
rpmbuild --rebuild /root/rpmbuild/SRPMS/<src.rpm_name>
```
Replace <src.rpm_name> with your modified source RPM package name. Example: kernel-5.10.134-13.1.1.al8.src.rpm.
```
rpmbuild --rebuild /root/rpmbuild/SRPMS/kernel-5.10.134-13.1.1.al8.src.rpm
```
The build takes significant time. The following output indicates success.