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I have installed ubuntu 20.04 on a qemu arm64 virtual machine. This is based on qemu's arm64 'virt' machine and I added a peripheral in the virtual machine. Now to test device driver, I need to build kernel module and I have to do it on my x86_64 ubuntu 20.04 machine.
Inside the VM, the uname -r command gives me 5.4.0-77-generic. I learned that I need the kernel source for this version(or is only the kernel header enough? this says I need kernel source.) . I have had trouble downloading a specific kernel version in the past and now I'm not sure how I should get this version.
From https://launchpad.net/ubuntu/focal/+source/linux-signed I can see some 5.4.0-77.86 versions under security and main but I'm not sure how these versions are different from 5.4.0-77-generic. Please anyone tell me how I can get this 5.4.0-77-generic kernel version source. Step by step instruction will be appreciated but any comment is welcome. Thanks! (The kernel.org site shows only some selected or recent versions.)

ADD :
After apt-cache search 5.4.0 I tried sudo apt install linux-cloud-tools-5.4.0-77-generic and it installs

/. /usr /usr/lib /usr/lib/linux-tools /usr/lib/linux-tools/5.4.0-77-generic /usr/share /usr/share/doc /usr/share/doc/linux-cloud-tools-5.4.0-77-generic /usr/share/doc/linux-cloud-tools-5.4.0-77-generic/copyright /usr/lib/linux-tools/5.4.0-77-generic/hv_fcopy_daemon /usr/lib/linux-tools/5.4.0-77-generic/hv_kvp_daemon /usr/lib/linux-tools/5.4.0-77-generic/hv_vss_daemon /usr/lib/linux-tools/5.4.0-77-generic/lsvmbus /usr/share/doc/linux-cloud-tools-5.4.0-77-generic/changelog.Debian.gz

I don't think this contains the kernel source.

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To build a standalone kernel driver, you only need your kernel's header. It can be installed throught the linux-headers-5.4.0-77-generic package. Don't mind about what is on repository, just:

  1. Make sure your package database is up-to-date by running as root apt update
  2. Install the required package with, still as root, apt install linux-headers-5.4.0-77-generic.

Usually, on ubuntu based distros, you'll have:

  • linux-image-<version> : The kernel by itself.
  • linux-headers-<version> : Kernel's header.
  • linux-source-<version> : Kernel's whole sources.
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  • Ah, thanks for the very succinct and clear answer! Commented Jul 13, 2021 at 13:14
  • But how come in my ubuntu 20.04 machine, I see linux-headers-5.4.0-77-generic and linux-image-5.4.0-77-generic for apt install candidates and not linux-source-5.4.0-77-generic? I see a candidate linux-source-5.4.0 - Linux kernel source for version 5.4.0 with Ubuntu patches which is the only source containing 5.4.0 pattern. (I understand I don't need the source). Commented Jul 13, 2021 at 13:22
  • I can't tell why the sources don't follow the same naming convention, nevertheless, linux-source-5.4.0 actually fetch 5.4.0.77 sources as you can see there: packages.ubuntu.com/focal/linux-source-5.4.0 Commented Jul 13, 2021 at 13:27
  • Oh, thanks so much again. I learned also that I have to check the package info at least :). Commented Jul 13, 2021 at 15:21
  • After installing the headers for 5.4, how do I boot into it? Commented Sep 23, 2021 at 3:58

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