I need btrfs filesystem support. I followed the wiki article and rebuilt the kernel, adding btrfs as a built-in kernel object. When I boot the new kernel and try to manually mount a btrfs filesystem, I get "mount: unknown filesystem type 'btrfs'". I have double-checked the config, and btrfs is definitely selected with an "*", as the wiki instructs.

However, my question concerns the new kernel itself. There is only one kernel file in /boot, the one I created on Mar 25. However, if I run "uname -a", it reports that the kernel was built on Mar 20, which is probably the day I originally installed Gentoo. It seems that the original kernel is the one being used, even though it apparently no longer exists.

Here is the boot line from the grub2 configuration:

linux /boot/kernel-genkernel-x86_64-3.12.13-gentoo root=/dev/sdb13
initrd /boot/initramfs-genkernel-x86_64-3.12.13-gentoo

/boot is not on a separate partition. Here is the requested output of ls -l:

lrwxrwxrwx 1 root root      42 Mar 25 14:57 System.map -> System.map-genkernel-x86_64-3.12.13-gentoo
-rw-r--r-- 1 root root 2101526 Mar 25 18:44 System.map-genkernel-x86_64-3.12.13-gentoo
lrwxrwxrwx 1 root root      41 Mar 25 14:58 initramfs -> initramfs-genkernel-x86_64-3.12.13-gentoo
-rw-r--r-- 1 root root 3481260 Mar 25 18:45 initramfs-genkernel-x86_64-3.12.13-gentoo
lrwxrwxrwx 1 root root      38 Mar 25 14:57 kernel -> kernel-genkernel-x86_64-3.12.13-gentoo
-rw-r--r-- 1 root root 3600976 Mar 25 18:44 kernel-genkernel-x86_64-3.12.13-gentoo

What am I missing?

Grub menu entry:

menuentry 'Gentoo Base System release 2.2 (on /dev/sdb13)' --class gnu-linux --class gnu --class os $menuentry_id_option 'osprober-gnulinux-simple-1e68823f-eec6-45b9-9563-a673ec07f4e3' {
        insmod part_gpt
        insmod ext2
        set root='hd1,gpt13'
        if [ x$feature_platform_search_hint = xy ]; then
          search --no-floppy --fs-uuid --set=root --hint-bios=hd1,gpt13 --hint-efi=hd1,gpt13 --hint-baremetal=ahci1,gpt13  1e68823f-eec6-45b9-9563-a673ec07f4e3
          search --no-floppy --fs-uuid --set=root 1e68823f-eec6-45b9-9563-a673ec07f4e3
        linux /boot/kernel-genkernel-x86_64-3.12.13-gentoo root=/dev/sdb13
        initrd /boot/initramfs-genkernel-x86_64-3.12.13-gentoo
  • Is /boot on a separate partition? Can you post the output of ls -l /boot?
    – casey
    Mar 26, 2014 at 16:36
  • Thanks for your response. I have edited the original post.
    – Tim
    Mar 26, 2014 at 16:38
  • Where is your grub config located at? I would expect to see the grub directory in that listing.
    – casey
    Mar 26, 2014 at 21:03
  • casey, I control grub from my main system (Debian) on another partition.
    – Tim
    Mar 26, 2014 at 21:06
  • That is probably your issue then, your /boot is not the /boot that grub is looking for. You need to put this kernel with your others within the partition that grub is configured to look in. Alternatively if you want to keep the kernel there, you need to modify the root= line in the grub config to point to this partition.
    – casey
    Mar 26, 2014 at 21:08

1 Answer 1


Ok, the problem was solved following advice given in Gentoo forums. That advice was to make the kernel manually instead of using genkernel. This worked perfectly, the first time.

cd /usr/src/linux
make menuconfig
make && make modules_install
cp arch/x86_64/boot/bzImage /boot
mv /boot/bzImage /boot/whatever_kernel_filename
genkernel --install initramfs

I am still confused as to why genkernel with --menuconfig does not seem to work as advertised. But I doubt that I will be trying it again. The manual way is not difficult.

  • Condense two lines into one with cp arch/x86_64/boot/bzImage /boot/whatever_kernel_filename rather than cp the kernel image and then mv it.
    – slackline
    Sep 26, 2014 at 6:30
  • What is meant by "whatever_kernel_filename" ? Example?
    – 에이바
    Mar 10, 2015 at 13:46
  • Thanks for posting the answer! It would be great of you could remember to accept it so the question can be marked as answered.
    – terdon
    Jun 15, 2015 at 17:17

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