How to Delete Old Unused Kernels in Debian and Ubuntu

In our last article, we’ve explained how to delete old unused kernels in CentOS/RHEL/Fedora. In this article, we will explain how to delete old unused kernels in Debian and Ubuntu systems, but before moving...

In our last article, we’ve explained how to delete old unused kernels in CentOS/RHEL/Fedora. In this article, we will explain how to delete old unused kernels in Debian and Ubuntu systems, but before moving further, you may want to install the latest version in order to take advantage of: security fixes, new kernel functions, updated drivers and so much more.

To upgrade your kernel to latest version in Ubuntu and Debian, follow this guide:

  1. How to Upgrade Kernel to Latest Version in Ubuntu

Important: It is advisable to keep at least one or two old kernels to fall back to in case there is a problem with an update.

To find out the current version of Linux kernel running on your system, use the following command.

$ uname -sr
Linux 4.12.0-041200-generic


To list all installed kernels on your system, issue this command.

$ dpkg -l | grep linux-image | awk '{print$2}'
linux-image-4.12.0-041200-generic
linux-image-4.8.0-22-generic
linux-image-extra-4.8.0-22-generic
linux-image-generic

Remove Old Unused Kernels on Debian and Ubuntu

Run the commands below to remove a particular linux-image along with its configuration files, then update grub2 configuration, and lastly reboot the system.

$ sudo apt remove --purge linux-image-4.4.0-21-generic
$ sudo update-grub2
$ sudo reboot

Removing Old Kernel in Ubuntu

[sudo] password for tecmint: Reading package lists... Done
Building dependency tree Reading state information... Done
The following additional packages will be installed:
linux-generic linux-headers-4.8.0-59 linux-headers-4.8.0-59-generic linux-headers-generic linux-image-4.8.0-59-generic linux-image-extra-4.8.0-59-generic linux-image-generic
Suggested packages:
fdutils linux-doc-4.8.0 | linux-source-4.8.0 linux-tools
Recommended packages:
thermald
The following packages will be REMOVED:
linux-image-4.8.0-22-generic* linux-image-extra-4.8.0-22-generic*
The following NEW packages will be installed:
linux-headers-4.8.0-59 linux-headers-4.8.0-59-generic linux-image-4.8.0-59-generic linux-image-extra-4.8.0-59-generic
The following packages will be upgraded:
linux-generic linux-headers-generic linux-image-generic
3 upgraded, 4 newly installed, 2 to remove and 182 not upgraded.
Need to get 72.0 MB of archives.
After this operation, 81.7 MB of additional disk space will be used.
Do you want to continue? [Y/n] y
Get:1 http://us.archive.ubuntu.com/ubuntu yakkety-updates/main amd64 linux-headers-4.8.0-59 all 4.8.0-59.64 [10.2 MB]
Get:2 http://us.archive.ubuntu.com/ubuntu yakkety-updates/main amd64 linux-headers-4.8.0-59-generic amd64 4.8.0-59.64 [811 kB] Get:3 http://us.archive.ubuntu.com/ubuntu yakkety-updates/main amd64 linux-generic amd64 4.8.0.59.72 [1,782 B] Get:4 http://us.archive.ubuntu.com/ubuntu yakkety-updates/main amd64 linux-headers-generic amd64 4.8.0.59.72 [2,320 B] Get:5 http://us.archive.ubuntu.com/ubuntu yakkety-updates/main amd64 linux-image-4.8.0-59-generic amd64 4.8.0-59.64 [23.6 MB] Get:6 http://us.archive.ubuntu.com/ubuntu yakkety-updates/main amd64 linux-image-extra-4.8.0-59-generic amd64 4.8.0-59.64 [37.4 MB] Get:7 http://us.archive.ubuntu.com/ubuntu yakkety-updates/main amd64 linux-image-generic amd64 4.8.0.59.72 [2,348 B] Fetched 72.0 MB in 7min 12s (167 kB/s) Selecting previously unselected package linux-headers-4.8.0-59.
(Reading database ... 104895 files and directories currently installed.)
Preparing to unpack .../0-linux-headers-4.8.0-59_4.8.0-59.64_all.deb ...
Unpacking linux-headers-4.8.0-59 (4.8.0-59.64) ...
Selecting previously unselected package linux-headers-4.8.0-59-generic.
Preparing to unpack .../1-linux-headers-4.8.0-59-generic_4.8.0-59.64_amd64.deb ...
Unpacking linux-headers-4.8.0-59-generic (4.8.0-59.64) ...
Preparing to unpack .../2-linux-generic_4.8.0.59.72_amd64.deb ...
Unpacking linux-generic (4.8.0.59.72) over (4.8.0.22.31) ...
Preparing to unpack .../3-linux-headers-generic_4.8.0.59.72_amd64.deb ...
Unpacking linux-headers-generic (4.8.0.59.72) over (4.8.0.22.31) ...
Selecting previously unselected package linux-image-4.8.0-59-generic.
Preparing to unpack .../4-linux-image-4.8.0-59-generic_4.8.0-59.64_amd64.deb ...
Done.
Removing linux-image-4.8.0-22-generic (4.8.0-22.24) ...
Examining /etc/kernel/postrm.d .
run-parts: executing /etc/kernel/postrm.d/initramfs-tools 4.8.0-22-generic /boot/vmlinuz-4.8.0-22-generic
update-initramfs: Deleting /boot/initrd.img-4.8.0-22-generic
run-parts: executing /etc/kernel/postrm.d/zz-update-grub 4.8.0-22-generic /boot/vmlinuz-4.8.0-22-generic
Generating grub configuration file ...
Found linux image: /boot/vmlinuz-4.12.0-041200-generic
Found initrd image: /boot/initrd.img-4.12.0-041200-generic
Found linux image: /boot/vmlinuz-4.8.0-59-generic
done
...

Although this method works just fine, it is more reliable and efficient to use a handy script called “byobu” that combines all the commands above into a single program with useful options such as specifying number of kernels to keep on the system.

Install byobu script package which provides a program called purge-old-kernels used for removing old kernels and header packages from the system.

$ sudo apt install byobu

Then remove old kernels like so (the command below allows 2 kernels to be kept on the system).

$ sudo purge-old-kernels --keep 2

You may also like to read these following related articles on Linux kernel.

  1. How to Load and Unload Kernel Modules in Linux
  2. How to Change Kernel Runtime Parameters in a Persistent and Non-Persistent Way

In this article, we have described how to remove old unused kernel images on Ubuntu and Debian systems. You can share any thoughts via the feedback from below.

Posted by wiredgorilla