By default, Proxmox allocates less than 300MB to the `/boot` partition during installation. Since Proxmox updates frequently, `/boot` can quickly fill up, leading to upgrade failures. The only solution in such cases is to manually delete old kernels.

The Problem

Proxmox, being based on Debian, installs both `debian linux-image` and `pve-kernel` whenever you run `apt update && apt dist-upgrade`. These packages occupy `/boot` space, so freeing up space involves removing old versions of these kernels.

Steps to Free Up /boot Space

1. Record the Current Kernel

   Note the kernel currently in use:  

   uname -mrs

2. List Old Kernels

   Find all installed kernels:  

3. Remove Old Kernels

   Remove outdated kernels with the following command:  

   apt purge linux-image-$old_version

Important Notes

If Proxmox fails to update due to insufficient `/boot` space, `update-grub` will also fail. However, there’s no need to worry. Every time you run `apt purge` on an old kernel, `update-grub` will automatically execute and set the latest kernel as the default boot entry.

If you want to manually set the default kernel for the next boot, use:  

Simplified Methods

To avoid constantly managing `/boot`, consider the following:

1.https://github.com/jordanhillis/pvekclean

2.During Proxmox installation, manually allocate 2GB for the `/boot` partition. This will reduce the frequency of cleanup tasks and provide a buffer for future updates.