New gemstone for determining kernel configs

docs/gemstones/view_kernel_conf.md

@@ -0,0 +1,82 @@
+---
+title: View Current Kernel Configuration
+author: David Hensley
+contributors:
+tested with: 8.5
+tags:
+  - kernel
+  - config
+  - modules
+  - kmod
+update: 09-Mar-2022
+---
+The Linux kernel stores running kernel information in two places via special filesystems located in memory:
+  - The older [procfs](https://man7.org/linux/man-pages/man5/procfs.5.html) which mounts `/proc` (verify via `mount -l -t proc`)
+  - The newer [sysfs](https://man7.org/linux/man-pages/man5/sysfs.5.html) which mounts `/sys` (verify via `mount -l -t sysfs`)
+
+[Concise summary](https://www.landoflinux.com/linux_procfs_sysfs.html) of them and what info they contain.
+
+Linux distributions store the config used to compile the kernel as an ASCII file in:
+```bash
+/lib/modules/<kernel-release>/build/.config
+```
+Configured builtin (statically compiled in) and loadable modules for the currently running kernel are listed by directories named for the modules in:
+```bash
+/sys/module/
+```
+See what your currently running "kernel release" version is with:
+
+`uname -r` and substitute its value in commands with `$(uname -r)`
+
+You can examine these files to make sure the currently running kernel was compiled with the functions you need:
+  - `cat /lib/modules/$(uname -r)/build/.config | grep -i <keyword>`
+  - `ls /sys/module/ | grep -i <keyword>`
+  - `sysctl -a | grep -i <keyword>`
+  - `lsmod | grep -i <keyword>`
+  - `modinfo <module>`
+
+You can check for kernel module dependencies in:
+```bash
+/lib/modules/<kernel-release>/modules.dep
+```
+but it is easier to read the output of the "Used-by" field in `lsmod`.
+
+RHEL and derivative distributions (Fedora, CentOS Stream, Scientific Linux, RockyLinux, Almalinux, et. al.) 
+also store the config used for bootable installed kernels in the `/boot` directory as ASCII files:
+```bash
+/boot/config-<kernel-release>
+```
+To check the currently running kernel config for a particular value:
+```bash
+cat /boot/config-$(uname -r) | grep -i <keyword>
+```
+Results will show 
+  - "=m" if compiled in as a kernel module
+  - "=y" if compiled statically into the kernel
+  - "is not set" if the setting exists but is not enabled (a boolean)
+If your search yields no results then the element you are looking for may depend on another config element which
+isn't set (check this with `lsmod`).
+
+Some distributions, like Gentoo and Arch, use `/proc/config.gz` by default instead:
+```bash
+zcat /proc/config.gz | grep -i <keyword>
+zgrep <keyword> /proc/config.gz
+```
+
+For any distribution, if your running kernel has set both
+```
+CONFIG_IKCONFIG
+CONFIG_IKCONFIG_PROC
+```
+and if
+```bash
+ls /sys/module/configs
+```
+exists and is executable (searchable in the case of a dir)
+then you can create `/proc/config.gz` with this command:
+```bash
+modprobe configs
+```
+### Reference:
+
+[sysctl](https://man7.org/linux/man-pages/man8/sysctl.8.html), [lsmod](https://man7.org/linux/man-pages/man8/lsmod.8.html), [modinfo](https://man7.org/linux/man-pages/man8/modinfo.8.html), [modprobe](https://man7.org/linux/man-pages/man8/modprobe.8.html), [depmod](https://man7.org/linux/man-pages/man8/depmod.8.html), [modules.dep](https://man7.org/linux/man-pages/man5/modules.dep.5.html), [procfs](https://man7.org/linux/man-pages/man5/procfs.5.html), [sysfs](https://man7.org/linux/man-pages/man5/sysfs.5.html), [uname](https://man7.org/linux/man-pages/man8/uname26.8.html)