Create kernel_panic page

docs/guides/kernel_panic.md

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+---
+title: How to deal with a kernel panic
+author: Antoine Le Morvan
+contributors: Steven Spencer
+tested_with: 9.4
+tags:
+  - kernel
+  - kernel panic
+  - rescue
+---
+
+# How to deal with a kernel panic
+
+Sometimes a kernel installation goes wrong and you have to backtrack.
+
+There can be many reasons for this: insufficient space on the `/boot` partition, an interrupted installation or some kind of problem with a third-party application.
+
+Fortunately for us, there's always something we can do to save the day.
+
+## Try to reboot with the previous kernel
+
+First thing to try is to reboot with the previous kernel.
+
+* Restart the system. 
+* Once you have reached the GRUB 2 boot screen, move the selection to the menu entry corresponding to the previous kernel and press the `enter` key.
+
+Once the system has restarted, it can be repaired.
+
+If the system does not boot, try the **rescue mode** (see above).
+
+## Uninstall the broken kernel
+
+The easiest way to do this is to uninstall the kernel version that's not working and then reinstall it.
+
+!!! NOTE
+
+    You can't remove a kernel that you are running. 
+
+    To show the version of currently running kernel: 
+
+    ```bash
+    uname -r
+    ```
+
+You can check the list of installed kernels:
+
+```bash
+dnf list installed kernel\* | sort -V
+```
+
+but this command is perhaps more practical, since it only returns packages that have several versions installed:
+
+```bash
+dnf repoquery --installed --installonly
+```
+
+To remove a specific kernel, you can use `dnf`, specifying the kernel version you retrieved earlier:
+
+```bash
+dnf remove kernel-core-<version>
+```
+
+Example:
+
+```bash
+dnf remove kernel-5.14.0-427.20.1.el9_4.x86_64
+```
+
+or use the `dnf repoquery` command:
+
+```bash
+dnf remove $(dnf repoquery --installed --installonly --latest=1)
+```
+
+You can now  upgrade your system to try to reinstall the latest kernel version.
+
+```bash
+dnf update
+```
+
+Reboot and see if this time, the new kernel works!
+
+## Rescue mode
+
+Rescue mode corresponds to the old single-user mode.
+
+!!! NOTE
+
+    To enter in rescue mode, you have to provide the root password.
+
+To enter rescue mode, the easiest way is to select the line starting with `0-rescue-*` in the grub menu.
+
+Another way is to edit any line of the grub menu (pressing 'e' key) and add `systemd.unit=rescue.target` at the end of the line that starts with `linux` and then press `ctrl+x` to boot the system into rescue mode.
+
+!!! NOTE
+
+    You are then in qwerty mode.
+
+Once you are in rescue mode and you have enter the root password, you can then repair your system.
+
+For that, you may need to configure a temporary IP address thanks to `ip ad add ...` (see network chapter of our admin guide).
+
+## Last chance: Anaconda Rescue Mode
+
+If none of the above methods work, it's still possible to boot from the installation ISO and repair the system.
+
+This method is not covered by this documentation. 
+
+## System maintenance
+
+### Cleaning old kernel versions
+
+You can remove old installed kernel packages, keeping only latest version and version of running kernel:
+
+```bash
+dnf remove --oldinstallonly
+```
+
+### Limiting the number of installed kernels versions
+
+We can limit the number of kernel versions by editing the `/etc/yum.conf` file and setting the **installonly_limit** variable:
+
+```text
+installonly_limit=3
+```
+
+!!! NOTE
+
+    You should always keep at least the latest kernel version and a backup version.