Creating a HackMyVM Virtualbox - Notes

Just a few notes (mainly for myself!)

After creating a new machine.... and running an export and checking the size - it looks larger than expected. I was using Virtualbox 6.1 and Debian 11 as the machine host, makes the install with Nginx & PHP around 330Mb.

Steps:

1. Keep the original backup (just in case!)

2. Remove any old\previous kernels. 

Find the current one with:

uname -sr

dpkg -l | grep linux-image | awk '{print$2}'

apt remove --purge <kernel name>

update-grub2

reboot

3. /var/logs

truncate -s 0 <logfile>

on any large logs.

4. Clean up apt

apt-get clean

and also delete the +100Mb in /var/lib/apt/lists (it will be recreated if you apt-get update)

reboot to check its still works and halt.

#Note if you export at this point it has not changed size :(

5.Attach the disk without mounting it (live Kali or Knoppix)

(if required)

apt-get install zerofree

(then assuming the disk is attached in /dev/sda1) 

zerofree -z /dev/sda1

it does a check and sets the bytes of deleted files to 00

6. Now do another export and the image has actually shrunk to a nice size!

References

https://www.tecmint.com/remove-old-kernel-in-debian-and-ubuntu/

https://computingforgeeks.com/how-to-empty-truncate-log-files-in-linux/

https://askubuntu.com/questions/179955/var-lib-apt-lists-is-huge#:~:text=These%20files%20are%20then%20stored,since%20the%20cache%20is%20empty).

https://askubuntu.com/questions/1253347/how-to-easily-remove-old-kernels-in-ubuntu-20-04-lts