pxelinux.cfg/

The pxelinux.cfg/ directory is a key component in a PXE (Preboot Execution Environment) boot setup. It contains configuration files that dictate how PXE clients (computers booting over the network) behave during the boot process. Here’s an overview of pxelinux.cfg/ and its purpose:

Purpose of pxelinux.cfg/

1. Configuration Storage:

   • pxelinux.cfg/ is a directory typically located on the TFTP (Trivial File Transfer Protocol) server used for PXE booting.

   • It stores configuration files that determine which boot options are available to PXE clients and how those options are configured.

2. File Naming Convention:

   • Configuration files within pxelinux.cfg/ follow a specific naming convention:

     • The filename can be based on either the MAC address of the PXE client’s network interface card (NIC) or the IP address of the client.

     • Alternatively, a default configuration file named default can be used to define global settings or fallback options for all PXE clients.

3. Configuration Options:

   • Each configuration file in pxelinux.cfg/ specifies various boot parameters, such as:

     • Kernel Image (KERNEL): Specifies the kernel file (vmlinuz) that the client should load.

     • Initial RAM Disk (INITRD): Specifies the initial RAM disk file (initrd.img) used during boot.

     • Kernel Arguments (APPEND): Provides additional arguments to be passed to the kernel during boot, such as root filesystem location, network settings, and other boot parameters.

     • Labels (LABEL): Defines different boot options or configurations within the same configuration file.

4. Default Configuration (default file):

   • The default file within pxelinux.cfg/ is used when no specific configuration file matches the client’s MAC address or IP address.

   • It can define a default boot option or menu structure that applies to all PXE clients unless overridden by a specific configuration file.

5. Customization:

   • Administrators can customize pxelinux.cfg/ to tailor boot options based on the requirements of different systems or network segments.

   • This customization allows for flexibility in deploying different operating systems, configurations, or rescue environments over the network.

Example Configuration

Here’s an example of what a pxelinux.cfg/ directory structure might look like:

pxelinux.cfg/
├── default
├── 01-23-45-67-89-ab-cd
├── 192.168.1.100
└── 192.168.1.101

• default: Contains the default boot configuration for all PXE clients.

• 01-23-45-67-89-ab-cd: Configuration file based on the MAC address of a specific client.

• 192.168.1.100 and 192.168.1.101: Configuration files based on the IP addresses of specific clients.

Configuration File Example

# Example configuration for a specific client (01-23-45-67-89-ab-cd)
LABEL linux
    KERNEL vmlinuz
    APPEND initrd=initrd.img root=/dev/nfs nfsroot=192.168.1.10:/path/to/nfs/root ip=dhcp

In this example:

• LABEL linux: Defines a label for the boot option.

• KERNEL vmlinuz: Specifies the kernel file to load.

• APPEND initrd=initrd.img root=/dev/nfs nfsroot=192.168.1.10:/path/to/nfs/root ip=dhcp: Appends additional boot parameters passed to the kernel.

Conclusion

pxelinux.cfg/ plays a crucial role in PXE boot environments by storing configuration files that determine how PXE clients boot over the network. Understanding and properly configuring pxelinux.cfg/ allows administrators to manage and deploy operating systems, recovery tools, and other utilities efficiently across networked computers.