How do I build the kernel in tmpfs?

Message

leyvi · Post by **leyvi** » Mon Oct 27, 2025 7:06 pm

Just the build directory, obviously.
Where do I mount tmpfs?

Post by Hu » Mon Oct 27, 2025 7:40 pm

Mount it wherever you like, and point the kernel build system to it by setting $KBUILD_OUTPUT to that path.

leyvi · Post by **leyvi** » Mon Oct 27, 2025 10:27 pm

Hu wrote:Mount it wherever you like, and point the kernel build system to it by setting $KBUILD_OUTPUT to that path.

Cool, thanks. Is that an environment variable or a make variable?

Post by Hu » Tue Oct 28, 2025 12:15 am

It is normally put in the environment.

mutiny · Post by **mutiny** » Sat Nov 01, 2025 5:29 pm

Out of curiosity, if portage is configured for tmpfs, does it build gentoo-kernel in tmpfs automatically with $KBUILD_OUTPUT or otherwise itself?

leyvi · Post by **leyvi** » Sat Nov 01, 2025 5:59 pm

Hu wrote:It is normally put in the environment.

This doesn't work for me. It says the build is messed up, and tells me to run a make thing called mrproper or something like that.

Post by Hu » Sat Nov 01, 2025 6:25 pm

mutiny wrote:Out of curiosity, if portage is configured for tmpfs, does it build gentoo-kernel in tmpfs automatically with $KBUILD_OUTPUT or otherwise itself?

As I read the eclass, it includes O= with appropriate values, in each invocation of make. As I read Documentation/admin-guide/README.rst, this should have the same effect. If I recall correctly, O= is only respected when set on the make command line. KBUILD_OUTPUT is respected when put in the process environment.

leyvi wrote:
Hu wrote:It is normally put in the environment.
This doesn't work for me. It says the build is messed up, and tells me to run a make thing called mrproper or something like that.

This has worked for me for years. Without further details of what you did, there is nothing I can do to debug your environment.

DaggyStyle · Post by **DaggyStyle** » Sat Nov 01, 2025 6:37 pm

something like this

Code: Select all

mount -t tmpfs -o size=2G tmpfs ${MNT_POINT}
zcat /proc/config.gz > ${MNT_POINT}/.config
make mrproper -C ${KERNEL_SRC_PATH}
make -C ${KERNEL_SRC_PATH} O=${MNT_POINT} oldconfig
make -C ${KERNEL_SRC_PATH} ${MAKEOPTS} O=${MNT_POINT}
make -C ${KERNEL_SRC_PATH} ${MAKEOPTS} O=${MNT_POINT} modules_install
umount ${MNT_POINT}

Post by **NeddySeagoon** » Sat Nov 01, 2025 7:34 pm

DaggyStyle,

Not quite like that. mrproper wipes out the .config file too, so that should be the first command .
It's probably not required though.

It would be a good idea to install the bzImage before umount too.