134

I accidentally deleted my .config for my kernel configuration on Linux, and seem to remember there was a way to retrieve the kernel configuration via the proc filesystem somehow.

Is this still possible, and if so how would I do it?

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132

Depending on your system, you'll find it in any one of these:

  1. /proc/config.gz
  2. /boot/config
  3. /boot/config-$(uname -r)

and possibly more places.

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  • 4
    On some distros (Fedora/Redhat) it's /boot/config-2.6.18-194.el5 or similar, with the kernel release string appended. – Phil May 23 '11 at 15:50
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    @Phil I run a distro (Zenwalk) where those filenames are symlinked by the latest kernel package to /boot/config. I'll go ahead and add these to the list - thanks for reminding me. – new123456 May 23 '11 at 20:15
  • in /boot/config-$(uname -r) for amazon linux and likely RHEL – aeb0 Nov 27 '16 at 23:47
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    Not existing such files on Ubuntu Mate or Kali Linux for RaspBerry Pi. – Sopalajo de Arrierez Oct 5 '17 at 23:23
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    You should mention that your first item (/proc) is only available if module "configs" is loaded – Andy Feb 27 '18 at 7:41
66

For an actual running kernel, one way to get the config file this is to

cat /proc/config.gz | gunzip > running.config

or,

zcat /proc/config.gz > running.config

Then running.config will contain the configuration of the running linux kernel.

However this is only possible if your running linux kernel was configured to have /proc/config.gz. The configuration for this is found in

  • General setup
    • [*] Kernel .config support
      • [*] Enable access to .config through /proc/config.gz

Most distributions do not have this configuration set. They provide kernel config files in their kernel packages and is usually found in /boot/ directory.

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    These are known as CONFIG_IKCONFIG and CONFIG_IKCONFIG_PROC, if you're grepping for them. – chronospoon Mar 26 '15 at 18:34
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    zcat /proc/config.gz works fine. – Quanlong Aug 22 '16 at 4:15
  • less /proc/config.gz also works fine – nocnokneo Aug 6 at 10:53
43

A Little bit late but maybe it helps someone. I didn't have /proc/config.gz nor /boot/config nor /boot/config-$(uname -r) on my Computer. I had to run modprobe configs as root. Then, /proc/config.gz was present

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  • Can confirm on Intel MIC embedded Linux (BusyBox), this is necessary and works. – Mark Lakata Feb 23 '16 at 18:59
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    Same for Raspbian on Raspberry Pi 2 – Drew McGowen Mar 24 '16 at 2:39
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    FATAL: Module configs not found. on OMV 2.2 (Debian Wheezy) so glad they provided it in /boot/config-$(uname -r) – tuk0z Apr 12 '16 at 11:42
  • You sir, saved my day. Have a +1 – Christian Jan 14 '18 at 10:26
  • 'modprobe configs' is very helpful I had tests that automatically probe kconfig that were failing on a Raspberry Pi 3, but now work. Thanks for the tip!! – Tim Bird Jan 3 '19 at 0:40
10

If you couldn't find kernel configuration in /boot/ nor in /proc/config.gz, you can try extracting this information from the kernel itself.

Inside any kernel source code there is a script for extracting config located in scripts/extract-ikconfig, pass the kernel you want its configuration as parameter to this script.

This solution will only work if Kernel .config support was enabled in the compiled kernel.

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  • 2
    This was extremely helpful and helped me to obtain plenty of configs I didn't expect to ever see. Thanks! – selurvedu Oct 2 '17 at 14:16
8

Independently of the distribution, you can run: cat /lib/modules/$(uname -r)/build/.config

Source: https://linux.die.net/man/5/proc (search for /proc/config).

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1

For RedHat-based distributions, the .config file of the off-the-shelf kernel can be found with the command cat /lib/modules/$(uname -r)/build/.config that's available after the package kernel-devel is installed using the command: 

yum -y install kernel-devel

Note that with the real Red Hat Enterprise Linux distribution, you will need to enable the source-repository to get this package. On RHEL8, use the following command to do that:

subscription-manager repos --enable=rhel-8-for-x86_64-baseos-source-rpms
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0

If you can't find any of the suggested files and you are able to modprobe you should almost always be able to get a copy of the current config this way.

modprobe configs # might need `sudo modprobe configs`

# This will create /proc/config.gz
zcat /proc/config.gz

# Or if you are looking for whether a specific option was set
zgrep USBIP /proc/config.gz
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  • Interesting idea, but I'm not sure enough kernels ship with the configs module available. I couldn't find it on the Ubuntu 18.04 or 20.04 systems I had handy. – Greg Smith Sep 8 at 0:40
  • I found it useful specifically on ChromeOS where they don't include the compressed configs but do include the module to export the running config if so desired. – dragon788 Sep 8 at 3:02

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