Safest way to clean up boot partition - Ubuntu 14.04LTS-x64, Ubuntu 16.04LTS-x64

Reference

Case I: if /boot is not 100% full and apt is working

1. Check the current kernel version

$ uname -r 

It will shows the list like below:

3.19.0-64-generic

2. Remove the OLD kernels

2.a. List the old kernel

$ sudo dpkg --list 'linux-image*'|awk '{ if ($1=="ii") print $2}'|grep -v `uname -r`

You will get the list of images something like below:

linux-image-3.19.0-25-generic
linux-image-3.19.0-56-generic
linux-image-3.19.0-58-generic
linux-image-3.19.0-59-generic
linux-image-3.19.0-61-generic
linux-image-3.19.0-65-generic
linux-image-extra-3.19.0-25-generic
linux-image-extra-3.19.0-56-generic
linux-image-extra-3.19.0-58-generic
linux-image-extra-3.19.0-59-generic
linux-image-extra-3.19.0-61-generic

2.b. Now its time to remove old kernel one by one as

$ sudo apt-get purge linux-image-3.19.0-25-generic
$ sudo apt-get purge linux-image-3.19.0-56-generic
$ sudo apt-get purge linux-image-3.19.0-58-generic
$ sudo apt-get purge linux-image-3.19.0-59-generic
$ sudo apt-get purge linux-image-3.19.0-61-generic
$ sudo apt-get purge linux-image-3.19.0-65-generic

When you're done removing the older kernels, you can run this to remove ever packages you won't need anymore:

$ sudo apt-get autoremove

And finally you can run this to update grub kernel list:

$ sudo update-grub

Case II: Can't Use apt i.e. /boot is 100% full

NOTE: this is only if you can't use apt to clean up due to a 100% full /boot

1. Get the list of kernel images

Get the list of kernel images and determine what you can do without. This command will show installed kernels except the currently running one

$ sudo dpkg --list 'linux-image*'|awk '{ if ($1=="ii") print $2}'|grep -v `uname -r`

You will get the list of images somethign like below:

linux-image-3.19.0-25-generic
linux-image-3.19.0-56-generic
linux-image-3.19.0-58-generic
linux-image-3.19.0-59-generic
linux-image-3.19.0-61-generic
linux-image-3.19.0-65-generic
linux-image-extra-3.19.0-25-generic
linux-image-extra-3.19.0-56-generic
linux-image-extra-3.19.0-58-generic
linux-image-extra-3.19.0-59-generic
linux-image-extra-3.19.0-61-generic

2. Prepare Delete

Craft a command to delete all files in /boot for kernels that don't matter to you using brace expansion to keep you sane. Remember to exclude the current and two newest kernel images. From above Example, it's

sudo rm -rf /boot/*-3.19.0-{25,56,58,59,61,65}-*

3. Clean up what's making apt grumpy about a partial install.

sudo apt-get -f install

4. Autoremove

Finally, autoremove to clear out the old kernel image packages that have been orphaned by the manual boot clean.

sudo apt-get autoremove

5. Update Grub

sudo update-grub

6. Now you can update, install packages

sudo apt-get update