Manjaro Kernels

Overview

As the name would imply, as with the kernel of a seed, the Linux kernel is the core of a Linux operating system. Every other element of a Linux-based operating system is built around the kernel, which acts as an interface between your computer's hardware and the applications that run on it. As hardware and software applications become more complex and sophisticated, so do the kernels to fully utilise them. As such, Linux kernels are continually under development, with new revisions and versions being regularly released. Further information on the very latest developments in kernel technology can be found at The Linux Kernel Archives

The first Linux kernel was originally developed by Linus Torvalds, the creator of Linux. As an open source project, although modern kernels now contain millions of lines of code generated by thousands of programmers, Linus Torvalds still has the final authority on their development and release.

Identifying the Kernel Being Used

If the existing Kernel being run in Manjaro is not immediately apparent (i.e. through the pre-installed Conky display on your desktop), then it can be shown by opening the terminal and then entering the following command:

mhwd-kernel -li

The above command not only shows which kernel is being used on my machine, it also lists any other kernels that are also installed, as shown in the following Terminal output:

[handy@jarmano ~]$ mhwd-kernel -li
Currently running: 3.10.1-1-MANJARO (linux310)
The following kernels are installed in your system:
   * linux310
   * linux38
   * linux39

As seen in the above example, Manjaro is running kernel 3.10.1-1-MANJARO. The information given here is not arbitrary; each part of the kernel name identifies something about that kernel:

• The 3 indicates the version
• The 10 indicates the major revision
• The 1 indicates the minor revision
• The 1 indicates bug fixing
• MANJARO indicates the specific distribution it is used for

Adding New Kernels

Tip

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mhwd-kernel will automatically update a newly installed kernel with any modules currently used in your existing kernel. For example, if you were to update from kernel 3.9 to 3.10, mhwd-kernel would automatically update 3.10 with any and all modules present in 3.9. How about that!

Manjaro not only supports the use of multiple kernels (selectable from the boot screen), but allows easy access to the very latest bleeding edge kernels as well. This is undertaken through use of Manjaro's own MHWD-kernel (Manjaro Hard-Ware Detection) command. The syntax of the command is as follows:

sudo mhwd-kernel [-i] [new kernel: linux(version)] [optional - remove the current kernel: rmc]

When listing a new kernel to be installed in the command, it is not necessary to write the entire version number. For example, any version of Kernel 3.9 can be listed simply as 'linux39', and any version of Kernel 3.10 can be listed as 'linux310', and so on.

The optional rmc (remove current) component is of vital importance. Using this will result in your existing kernel being deleted upon the installation of the new kernel. Otherwise, if it is not used, then the existing kernel will be kept, and will be selectable alongside the new kernel at the boot screen. It is recommended - especially if updating to the latest bleeding edge kernel - to keep your old one, even if only for a short time afterwards. This the safer option, and the old kernel can be easily removed when satisfied with the stability and functionality of the new one.

As an example, once the terminal is opened, the following command will install a new kernel (3.10) without deleting the existing kernel currently being used:

sudo mhwd-kernel -i linux310

Otherwise, the following command will install a new kernel (3.10) to replace the existing kernel, which will be deleted:

sudo mhwd-kernel -i linux310 rmc

Either way, Manjaro will automatically configure the new kernel for you, ready for immediate use. Once completed, close the terminal and re-boot the system for the change to take effect.

Removing Kernels

Warning

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DO NOT attempt to delete an existing kernel while it is actually being used by Manjaro at the time. You can first identify what kernel is running on your system by using the command mhwd-kernel -li in the terminal (see above).

Where multiple kernels are present on your system, pacman can be used to remove them in the terminal. It may be necessary to delete a total of three elements of the kernel in total to completely remove it:

1. The kernel itself
2. The kernel's headers
3. The kernel's extra modules

Whether or not the headers and extra modules must be deleted depends on whether or not they have been installed.

1. To remove a kernel use the following syntax:

sudo mhwd-kernel -R linux[version]

Here is an example for removing kernel 3.9.10-1

sudo mhwd-kernel -R linux39

2. To delete a kernel's headers, the syntax is:

sudo pacman -R linux[version]-headers

For example, to delete the headers of kernel version 3.9 from the system, the following command would be entered:

sudo pacman -R linux39-headers

3. To delete a kernel's extra modules, the syntax is:

sudo pacman -R linux[version]-extramodules

For example, to delete the extra modules of kernel version 3.9 from the system, the following command would be entered:

sudo pacman -R linux39-extramodules

4. To delete all elements of a kernel at the same time - where they are all present on your system - the syntax is:

sudo pacman -R linux[version] linux[version]-headers linux[version]-extramodules

For example, to completely remove all elements of kernel version 3.9, the following command would be entered:

sudo pacman -R linux39 linux39-headers linux39-extramodules

Please note however, that attempting to delete multiple elements at once if they are not present on your system will result in an error message before the operation itself is aborted. It is also worthwhile noting if Manjaro is being run in a virtual machine (e.g. Oracle Virtualbox), you may not be able to delete certain kernels if they contain elements important to the virtualisation process itself.

Selecting Kernels

All available kernels installed on your system will be presented upon booting up. As illustrated, this includes backup copies of each kernel version installed (which will also be automatically removed if or when a kernel version is deleted). To select a kernel, simply use the arrow keys to highlight the desired version, and then press <enter>.

Where a selection is not made, Manjaro will usually automatically select a kernel version after waiting five seconds for a key entry. The version automatically selected will usually be the one used previously.

Don't forget the mhwd-kernel -h command

As with most Linux commands that can be entered into the Terminal, typing the command followed by either -h or --help will print out the usage & available options to the Terminal for your reference. Here is the output of the mhwd-kernel -h command:

[handy@jarmano ~]$ mhwd-kernel -h
Usage: mhwd-kernel [option]
   -h  --help              Show this help message
   -i  --install           Install a new kernel        [kernel(s)] [optional: rmc = remove current kernel]
   -l  --list              List all available kernels
   -li --listinstalled     List installed kernels
   -r  --remove            Remove a kernel             [kernel(s)]

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