How To - Fix Boot Partition Too Small Issue

The situation: apt upgrade is failing because the system is trying to install a new kernel, and there are already two kernels installed, and you made your damn /boot/ partition too small.

Further details:

• Debian (specifically Proxmox in this example)
• Using encrypted LVM with unencrypted /boot/ and /boot/efi/ partitions

Example Error:

update-initramfs: Generating /boot/initrd.img-6.8.4-3-pve
zstd: error 70 : Write error : cannot write block : No space left on device 
E: mkinitramfs failure zstd -q -9 -T0 70
update-initramfs: failed for /boot/initrd.img-6.8.4-3-pve with 1.
dpkg: error processing package initramfs-tools (--configure):
 installed initramfs-tools package post-installation script subprocess returned error exit status 1
Errors were encountered while processing:
 initramfs-tools

Solution:

1. Identify the installed kernels: ls /boot/

root@hostname:~# ls /boot/
config-5.15.107-2-pve  config-6.2.16-3-pve	  initrd.img-5.15.108-1-pve  initrd.img-6.8.4-3-pve	System.map-5.15.108-1-pve  System.map-6.8.4-3-pve  vmlinuz-6.2.16-20-pve
config-5.15.108-1-pve  config-6.8.4-3-pve	  initrd.img-6.2.16-12-pve   lost+found			System.map-6.2.16-12-pve   vmlinuz-5.15.107-2-pve  vmlinuz-6.2.16-3-pve
config-6.2.16-12-pve   grub			  initrd.img-6.2.16-20-pve   pve			System.map-6.2.16-20-pve   vmlinuz-5.15.108-1-pve  vmlinuz-6.8.4-3-pve
config-6.2.16-20-pve   initrd.img-5.15.107-2-pve  initrd.img-6.2.16-3-pve    System.map-5.15.107-2-pve	System.map-6.2.16-3-pve    vmlinuz-6.2.16-12-pve

1. Identify the running kernel: uname -r

root@hostname:~# uname -r
6.2.16-12-pve  

1. Find the package name for the non-running kernel: apt list --installed | grep pve-kernel

(NOTE: This example was done on a Proxmox machine; on most Debian systems, you'll need to search for 'linux-image' instead)

root@hostname:~# apt list --installed | grep pve-kernel

WARNING: apt does not have a stable CLI interface. Use with caution in scripts.

pve-kernel-5.15.107-2-pve/now 5.15.107-2 amd64 [installed,local]
pve-kernel-5.15.108-1-pve/now 5.15.108-1 amd64 [installed,local]
pve-kernel-5.15/now 7.4-4 all [installed,local]
pve-kernel-6.2.16-3-pve/stable,now 6.2.16-3 amd64 [installed,auto-removable]
pve-kernel-6.2/stable,now 8.0.5 all [installed,automatic]

1. Use apt purge to remove all versions of the non-running kernel. Don't worry if the first one fails with the same update-initramfs error; you may need to remove more than one older kernel to free enough space for the kernel to update.