Check GCC Search Path for Kernel Headers in GNU/Linux

To check if GCC searches for kernel headers in /usr/src/kernels/ (common for kernel module development), use:

gcc -E -Wp,-v - </dev/null 2>&1 | grep "/usr/src/kernels"

Explanation

  • gcc -E -Wp,-v - </dev/null - -E: Stop after preprocessing (shows include paths). - -Wp,-v: Pass verbose flag to the preprocessor. - </dev/null: Empty input (avoids waiting for stdin).

  • 2>&1: Redirects stderr to stdout (GCC outputs paths to stderr).

  • grep "/usr/src/kernels": Filters output to show only matching paths.

Expected Output

If GCC includes /usr/src/kernels, the output will resemble:

/usr/src/kernels/5.15.0-78-generic/include

If no output appears, GCC does not search there.

View All Include Paths

To list all GCC header search paths:

gcc -E -Wp,-v - </dev/null 2>&1 | grep "^ "

Purpose of /usr/src/kernels

  • Required for compiling kernel modules (e.g., #include <linux/module.h>).

  • Typical locations:

    • Debian/Ubuntu: /usr/src/linux-headers-$(uname -r)/

    • RHEL/Fedora: /usr/src/kernels/

Install Missing Headers

  • Debian/Ubuntu:

    sudo apt install linux-headers-$(uname -r)

  • RHEL/Fedora:

    sudo dnf install kernel-devel