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How do I check what options are compiled into a Linux kernel without looking at /boot/config-* and if I don't have access to the /boot/config-* file that's left over?

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Unless your kernel was built with CONFIG_IKCONFIG_PROC, which would make the config available in /proc as sysadmin1138 mentioned above, you're pretty much out of luck. Debian and RH based kernel packages do, however, generally install a config-$version file in /boot. So unless it's a custom kernel, it should be available there.

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I believe /proc/config.gz contains the .config file the kernel was compiled with.

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    That's only available if CONFIG_IKCONFIG_PROC was set when the kernel was built. Doesn't seem to be there by default on RHEL or Ubuntu.
    – Insyte
    Commented Aug 6, 2009 at 17:19
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    As of writing, this is enabled by default on Arch :)
    – Navin
    Commented Apr 25, 2013 at 0:33
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    to read (or grep) the current settings from config.gz you can unzip it with $cat /proc/config.gz | gunzip > mykernel.conf as suggested by Jarl on superuser.com.
    – xaa
    Commented Oct 29, 2015 at 10:59
  • It is the case on Arch Linux as CONFIG_IKCONFIG_PROC=y.
    – Terry Wang
    Commented Jan 4, 2018 at 5:11
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    @xaa Or you can use the single command alternatives zcat or zless, the latter of which is more convenient as it is a pager which allows you to scroll and search as well.
    – comfreak
    Commented Aug 28, 2019 at 18:45

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