Kernel Command Line Parameters

This guide explains how to configure Lunar Linux's device node handling at boot time using kernel command line parameters passed through your bootloader.

Background: Device Node Management

Every Linux system requires device nodes to communicate with hardware. There are two main approaches to creating these nodes:

Static Device Nodes

• Device nodes exist permanently on a real filesystem (ext3, XFS, ReiserFS, etc.)
• All nodes are pre-created or manually created with mknod
• Nodes persist across reboots
• Managed with tools like makedev

Dynamic Device Nodes

Nodes are created automatically from hotplug events as hardware is detected.

devfs (Deprecated)

• Device nodes created in kernel space
• Uses a virtual filesystem
• Part of the kernel tree
• Used primarily with 2.4 kernels
• Status: Removed from modern kernels

udev (Modern Standard)

• Device nodes created in userspace
• Created by a userland application
• Lives outside the kernel tree
• Can exist on any filesystem (typically tmpfs/ramfs)
• Standard for 2.6+ kernels

Current Status

• 2.4 kernels: Primarily use devfs
• 2.6+ kernels: Use udev exclusively
• Static nodes: Still supported but less common

The dev= Parameter

Lunar Linux uses the dev= kernel parameter to specify device node handling:

dev=static    # Use static device nodes
dev=devfs     # Use devfs (2.4 kernels only)
dev=udev      # Use udev (2.6+ kernels)

Behavior on 2.4 Kernels

Valid options:

• dev=devfs
• dev=static

Automatic fallback behavior:

If no dev= parameter is specified or an invalid value is used:

1. Test for devfs and attempt to use it if available
2. Fall back to static device nodes if devfs is unavailable

Note: Using dev=udev on 2.4 kernels displays a warning and falls back to normal 2.4 behavior.

Behavior on 2.6+ Kernels

Valid options (tested in this order):

• dev=udev
• dev=devfs
• dev=static

Automatic detection:

If no dev= parameter is specified, Lunar tests for udev, then devfs, then static nodes in that order.

Configuring Bootloaders

LILO Configuration

Add kernel parameters using the append directive in /etc/lilo.conf:

image=/boot/vmlinuz
    label=awesomekernel
    root=/dev/hda2
    append="dev=udev video=radeonfb:1152x864-16@60"

Multiple parameters can be space-separated within the quotes.

Interactive mode:

If you have prompt set in lilo.conf, you can type parameters at boot time:

boot: awesomekernel dev=udev

After modifying /etc/lilo.conf, always run:

lilo

GRUB Configuration

Add parameters directly after the kernel path in /boot/grub/grub.conf or /boot/grub/menu.lst:

title Awesome Kernel
    root (hd0,1)
    kernel /boot/vmlinuz root=/dev/hda1 dev=udev video=radeonfb:1152x864-16@60

Interactive mode:

Press e to edit the kernel line at boot time, add your parameters, and press b to boot.

GRUB changes take effect immediately without running any additional commands.

GRUB2 Configuration

For modern systems using GRUB2, edit /etc/default/grub:

GRUB_CMDLINE_LINUX="dev=udev"

Then regenerate the configuration:

grub-mkconfig -o /boot/grub/grub.cfg

Common Use Cases

Force Static Device Nodes

# LILO
append="dev=static"

# GRUB
kernel /boot/vmlinuz root=/dev/hda1 dev=static

Specify udev Explicitly

# LILO
append="dev=udev"

# GRUB
kernel /boot/vmlinuz root=/dev/hda1 dev=udev

Combine with Other Parameters

Device parameters can be combined with other kernel options:

# LILO
append="dev=udev quiet splash acpi=off"

# GRUB
kernel /boot/vmlinuz root=/dev/hda1 dev=udev quiet splash acpi=off

Troubleshooting

System Won't Boot with udev

Symptoms:

• Kernel panic about missing root device
• Unable to mount root filesystem

Solutions:

1. Boot with dev=static parameter temporarily
2. Verify udev is installed: lin udev
3. Check that udev is enabled in your kernel configuration
4. Verify /etc/udev/ directory exists and is properly configured

devfs Not Found

Symptoms:

• Warning messages about missing devfs
• System falls back to static nodes

Solutions:

1. Verify devfs is compiled into your kernel (2.4 only)
2. Use dev=udev instead (for 2.6+ kernels)
3. Use dev=static if you prefer static nodes

Module Loading Issues

If hardware modules aren't loading automatically:

1. Ensure udev is installed and running
2. Check /etc/udev/rules.d/ for custom rules
3. Verify hotplug support in kernel
4. Review dmesg output for errors

Verifying Your Configuration

Check Current Device System

# Check if udev is running
ps aux | grep udev

# Check mounted filesystems
mount | grep dev

# View device node creation method
ls -la /dev

Test Different Configurations

You can test different device systems without permanently modifying your bootloader by using interactive mode at boot time.

Additional Kernel Parameters

While this guide focuses on device management, other useful boot parameters include:

• root=/dev/sda1 - Specify root filesystem
• ro / rw - Mount root read-only or read-write
• quiet - Reduce kernel messages during boot
• splash - Enable graphical boot splash
• single - Boot into single-user mode
• init=/bin/bash - Override init (useful for recovery)

See Also

• Complete Installation Guide
• Software RAID Installation
• Kernel Configuration
• man bootparam
• Linux Kernel Parameters List

Copyright: Copyleft Jaime Buffery, 2004-2005 nestu AT lunar-linux DOT org