/boot is full? Remove old kernels on Ubuntu, Debian, Fedora and RHEL

In a hurry? whyfull checks for this and every other common cause in one command.

Every kernel update installs a new kernel next to the old ones. Each kernel uses space in /boot (the kernel image and initramfs) and in /lib/modules, often 300 MB or more in total. When /boot is a small separate partition, a few updates are enough to fill it, and then the next update fails.

Remove old kernels with the package manager, never by deleting files from /boot by hand. That leaves the package database pointing at files that don't exist.

First, see what you're running

uname -r

Keep the running kernel and the newest installed one. Everything older can usually go.

Ubuntu and Debian

List installed kernels:

dpkg --list 'linux-image-*' | grep '^ii'

Remove the ones apt considers unused:

sudo apt autoremove --purge

If old kernels are still listed afterwards, they were installed manually. Purge them by name, for example:

sudo apt purge linux-image-6.8.0-31-generic linux-modules-6.8.0-31-generic

When apt fails because /boot is already full: apt can't finish anything until it has room, including the removal. Purge the oldest kernel directly with dpkg, then let apt fix the rest:

sudo dpkg --purge linux-image-6.8.0-31-generic
sudo apt --fix-broken install
sudo apt autoremove --purge

Fedora, RHEL, Rocky and AlmaLinux

dnf keeps a set number of kernels (installonly_limit, 3 by default). Remove all but the newest ones:

sudo dnf remove --oldinstallonly

To keep fewer from now on, set installonly_limit=2 in /etc/dnf/dnf.conf.

openSUSE

sudo zypper purge-kernels

Which kernels it keeps is set by multiversion.kernels in /etc/zypp/zypp.conf.

Arch Linux

Arch replaces the kernel on each update rather than keeping old versions, so old kernels don't pile up. If /boot is full there, look for extra kernels you installed (linux-lts, linux-zen) or leftover fallback images.