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I am trying to install a PREEMPT_RT kernel for my ubuntu distribution as this is a requirement for a robot I am working on. But no matter what I do I get errors when compiling the kernel. I've included the error messages in the question, and I have provided links for full terminal outputs. I am not very expreienced with linux, so I have been following setup-guides from the manufacturer with the following steps:

curl -SLO https://www.kernel.org/pub/linux/kernel/v5.x/linux-5.6.19.tar.xz
curl -SLO https://www.kernel.org/pub/linux/kernel/projects/rt/5.6/older/patch-5.6.19-rt12.patch.xz

xz -d linux-5.6.19.tar.xz
xz -d patch-5.6.19-rt12.patch.xz

tar xf linux-5.6.19.tar
cd linux-5.6.19
patch -p1 < ../patch-5.6.19-rt12.patch

make oldconfig

In the configuration I simply select Fully Preemptible Kernel (RT) (PREEMPT_RT_FULL) for the preemption model, and leave all the other settings at their default.

fakeroot make -j4 deb-pkg

dpkg-buildpackage: error: fakeroot -u debian/rules clean subprocess returned exit status 1 make2: *** [scripts/Makefile.package:77: deb-pkg] Error 1 make: *** [Makefile:1429: deb-pkg] Error 2

All terminal output here

If I instead try to use

sudo make -j4 deb-pkg

make3: *** [debian/rules:6: build] Error 2 dpkg-buildpackage: error: debian/rules build subprocess returned exit status 2 make2: *** [scripts/Makefile.package:77: deb-pkg] Error 2 make: *** [Makefile:1429: deb-pkg] Error 2

All termial output here

When that didn't work I tried following the steps given in the answer to this question

curl -SLO https://www.kernel.org/pub/linux/kernel/v5.x/linux-5.6.19.tar.gz
curl -SLO https://www.kernel.org/pub/linux/kernel/projects/rt/5.6/older/patch-5.6.19-rt12.patch.gz
tar xvzf linux-5.6.19.tar.gz
cd linux-5.6.19
gzip -cd ../patch-5.6.19-rt12.patch.gz | patch -p1 --verbose
make menuconfig

patch, menuconfig

make -j4
sudo make modules_install -j4

sudo make modules_install -j4 sed: can't read modules.order: No such file or directory make: *** [Makefile:1316: modinst] Error 2

make

sudo make modules -j4
sudo make modules_install -j4

When I use the make modules command it compiles for a long time and it terminates successfully, but once again when I run modules_install I get an error message:

cp: cannot stat 'modules.builtin': No such file or directory make: *** [Makefile:1317: modinst] Error 1

I am at a loss for what to try next. I have tried different kernel versions and different operating systems (Ubuntu 18.04 and 20.04), and I get the same error in all of them. The instructions I have been given seems so clear and direct, so I'm wondering if I'm doing something wrong, or if there is some hardware incompatibilites or something of that nature? For reference I am currently running Ubuntu 20.04.02, kernel 5.8.0-53-generic, hardware. Does anyone have any Idea what may cause this issue?

PS: this is my first question on this site, feedback on question format is appreciated (too much/to little/ relevance of information etc.) I just added all the information the terminal gave me, not sure what is or isn't useful

1

I was able to build the PREEMPT-RT kernel on Ubuntu 20.04 mostly based on this guide as follows:

sudo apt install build-essential git libssl-dev libelf-dev flex bison

Download kernel source and patch for that version:

wget https://mirrors.edge.kernel.org/pub/linux/kernel/v5.x/linux-5.4.143.tar.xz
wget https://mirrors.edge.kernel.org/pub/linux/kernel/projects/rt/5.4/patch-5.4.143-rt64-rc2.patch.xz

Unpack and apply patches:

tar -xf linux-5.4.143.tar.xz
cd linux-5.4.143
xzcat ../patch-5.4.143-rt64-rc2.patch.xz | patch -p1

Configure, and when asked for Preemption Model select the Fully Preemptible Kernel. Accept the default value for the rest:

cp /boot/config-5.4.0-81-generic .config
make oldconfig

Edit the .config file and change CONFIG_SYSTEM_TRUSTED_KEYS="debian/canonical-certs.pem" to CONFIG_SYSTEM_TRUSTED_KEYS=""

Build kernel:

make -j8 deb-pkg

Install the generated packages, and reboot your system.

sudo dpkg -i ../linux-headers-5.4.143-rt64-rc2_5.4.143-rt64-rc2-1_amd64.deb ../linux-image-5.4.143-rt64-rc2_5.4.143-rt64-rc2-1_amd64.deb ../linux-libc-dev_5.4.143-rt64-rc2-1_amd64.deb

After reboot you should be able to see something like this:

# uname -a
Linux vod 5.4.143-rt64-rc2 #1 SMP PREEMPT_RT Tue Sep 7 20:19:55 UTC 2021 x86_64 x86_64 x86_64 GNU/Linux

The guide suggests a few other steps but I haven't tested them yet.

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