How to use the command 'dracut' (with examples)

Dracut is a command-line tool used to generate initramfs images for booting the Linux kernel. It provides options to configure the generation process and uses configuration files in /etc/dracut.conf, /etc/dracut.conf.d/*.conf, and /usr/lib/dracut/dracut.conf.d/*.conf by default. This article will explore various use cases of the dracut command.

Use case 1: Generate an initramfs image for the current kernel without overriding any options

Code:

dracut

Motivation:

Sometimes, it becomes necessary to generate an initramfs image, especially during kernel updates, to ensure proper boot-up. By using the dracut command without any options, it generates an initramfs image for the current kernel, taking into account the existing configuration options.

Explanation:

• dracut: The command itself calls the dracut tool to generate the initramfs image.

Example output:

dracut: dracut module 'usrmount' will not be installed, because command 'mount' could not be found!
dracut: dracut module 'busybox' will not be installed, because command 'busybox' could not be found!
dracut: dracut module 'dash' will not be installed, because command 'dash' could not be found!
dracut: dracut module 'dash-static' will not be installed, because command 'dash' could not be found!
dracut: dracut module 'mdraid' will not be installed, because command 'mdadm' could not be found!
*** Creating image file ***
*** Creating image file done ***
*** Creating initramfs image file '/boot/initramfs-5.4.0-84-generic.img' done ***

Use case 2: Generate an initramfs image for the current kernel and overwrite the existing one

Code:

dracut --force

Motivation:

Occasionally, it may be necessary to overwrite the existing initramfs image to ensure the latest changes or updates are incorporated into the boot process. By using the --force option, the dracut command will overwrite the existing initramfs image for the current kernel.

Explanation:

• --force: This option forces dracut to overwrite any existing initramfs image without prompting for confirmation.

Example output:

*** Creating image file ***
*** Creating image file done ***
*** Creating initramfs image file '/boot/initramfs-5.4.0-84-generic.img' done ***

Use case 3: Generate an initramfs image for a specific kernel

Code:

dracut --kver kernel_version

Motivation:

In some scenarios, there may be multiple installed kernels on the system, and it becomes necessary to generate an initramfs image for a specific kernel. The --kver option allows us to specify the kernel version for which we want to generate the initramfs image.

Explanation:

• --kver kernel_version: This option specifies the kernel version for which the initramfs image should be generated.

Example output:

*** Creating image file ***
*** Creating image file done ***
*** Creating initramfs image file '/boot/initramfs-5.10.0-1051-oem.img' done ***

Use case 4: Show a list of available modules

Code:

dracut --list-modules

Motivation:

The dracut command also provides an option to list all available modules that can be used during the initramfs generation process. This can be helpful when customizing the generation process or troubleshooting boot-related issues.

Explanation:

• --list-modules: This option displays a list of available modules that can be used with the dracut command.

Example output:

10menu
90crypt
95lvm
96fcoe
97dasd
...

Conclusion:

The dracut command is a versatile tool for generating initramfs images for booting the Linux kernel. By understanding the various use cases and options described in this article, users can effectively generate and customize their initramfs images based on their specific requirements.