Ubuntu's method for removing redundant kernels

Step 1: View the current kernel

rew $ uname -a
Linux rew 4.15.0-42-generic #45~16.04.1-Ubuntu SMP Mon Nov 19 13:02:27 UTC 2018 x86_64 x86_64 x86_64 GNU/Linux

The current version is 4.15.0-42-ES5en

Step 2: Look at all the kernels

rew $ dpkg --get-selections | grep linux
console-setup-linux           install
libselinux1:amd64            install
libselinux1:i386            install
linux-base               install
linux-firmware             install
linux-generic-hwe-16.04         install
linux-headers-4.15.0-42         install
linux-headers-4.15.0-39         install
linux-headers-4.15.0-39-generic     install
linux-headers-4.15.0-42-generic     install
linux-headers-generic-hwe-16.04     install
linux-image-4.15.0-39-generic      install
linux-image-4.15.0-42-generic      install
linux-image-generic-hwe-16.04      install
linux-libc-dev:amd64          install
linux-libc-dev:i386           install
linux-modules-4.15.0-39-generic     install
linux-modules-4.15.0-42-generic     install
linux-modules-extra-4.15.0-39-generic  install
linux-modules-extra-4.15.0-42-generic  install
linux-sound-base            install
pptp-linux               install
syslinux                install
syslinux-common             install
syslinux-legacy             install
util-linux               install

Step 3: Remove the redundant kernel

All 39 versions are redundant to me, delete:

rew $ sudo apt-get remove \
linux-headers-4.15.0-39 \
linux-headers-4.15.0-39-generic \
linux-image-4.15.0-39-generic \
linux-modules-4.15.0-39-generic \
linux-modules-extra-4.15.0-39-generic

Check again after unloading:

rew $ dpkg --get-selections | grep linux
console-setup-linux           install
libselinux1:amd64            install
libselinux1:i386            install
linux-base               install
linux-firmware             install
linux-generic-hwe-16.04         install
linux-headers-4.15.0-42         install
linux-headers-4.15.0-42-generic     install
linux-headers-generic-hwe-16.04     install
linux-image-4.15.0-39-generic      deinstall
linux-image-4.15.0-42-generic      install
linux-image-generic-hwe-16.04      install
linux-libc-dev:amd64          install
linux-libc-dev:i386           install
linux-modules-4.15.0-39-generic     deinstall
linux-modules-4.15.0-42-generic     install
linux-modules-extra-4.15.0-39-generic  deinstall
linux-modules-extra-4.15.0-42-generic  install
linux-sound-base            install
pptp-linux               install
syslinux                install
syslinux-common             install
syslinux-legacy             install
util-linux               install

deinstall is uninstalled. If you don't feel comfortable with it, you can use purge to completely delete it from the configuration file and clean up the kernel list

rew $ sudo apt-get purge \
linux-headers-4.15.0-39 \
linux-headers-4.15.0-39-generic \
linux-image-4.15.0-39-generic \
linux-modules-4.15.0-39-generic \
linux-modules-extra-4.15.0-39-generic

Step 4: Update the system boot

After removing the kernel, you need to update the grub to remove the failed boot item

rew $ sudo update-grub # Choose according to circumstances grub/grub2