# Debian Kernel and Modules

The kernel is Debian's core OS. Modules are pluggable drivers and features.

## Kernel Info

Show running kernel version:

```bash
uname -r
uname -a           # verbose
```

Check available kernel images:

```bash
dpkg -l | grep linux-image
```

## Kernel Upgrade

Check for newer kernel:

```bash
sudo apt update
apt search linux-image
```

Install new kernel:

```bash
sudo apt install linux-image-amd64     # meta-package (recommended)
```

Then reboot:

```bash
sudo reboot
```

After reboot, verify:

```bash
uname -r
```

Remove old kernels (frees space):

```bash
sudo apt autoremove
```

## Modules

Loadable kernel modules extend functionality without reboot. List loaded:

```bash
lsmod
lsmod | grep nvidia
```

Load module:

```bash
sudo modprobe e1000        # Ethernet driver
```

Unload module:

```bash
sudo rmmod e1000
```

Check module info:

```bash
modinfo e1000
```

## Module Configuration

Persist module loading in `/etc/modules-load.d/`:

```bash
echo "ip_forward" | sudo tee /etc/modules-load.d/ip-forward.conf
```

Or `/etc/modules` (older):

```bash
echo "ip_forward" | sudo tee -a /etc/modules
```

Module options in `/etc/modprobe.d/`:

```bash
echo "options e1000 debug=1" | sudo tee /etc/modprobe.d/e1000.conf
```

Apply:

```bash
sudo update-initramfs -u
```

## Boot Process

1. BIOS/UEFI loads bootloader
2. Bootloader (GRUB) loads kernel and initramfs
3. initramfs is tiny filesystem with essential modules/tools
4. Kernel extracts initramfs into RAM, mounts root, runs init
5. `systemd` (PID 1) starts services

Bootloader config:

```bash
sudo nano /etc/default/grub
sudo update-grub
```

Rebuild initramfs (after major changes):

```bash
sudo update-initramfs -u -k all
```

## Kernel Parameters

Set at boot via GRUB cmdline. Edit `/etc/default/grub`:

```
GRUB_CMDLINE_LINUX="quiet splash acpi_osi="
```

Apply:

```bash
sudo update-grub
```

View current parameters:

```bash
cat /proc/cmdline
```

## Common Issues

- Module not loading → check `journalctl`, verify hardware compatibility
- Kernel panic → likely hardware or driver issue
- High memory use → `htop` to identify processes
- Old kernel booting → check GRUB default in `/etc/default/grub`