VM Snapshots

One of the coolest features of VMs is the ability to take "snapshots". You are, in essence, saving the state of a VM at that instant in time -- this includes what is loaded in memory, shown on the screen, etc. You can then roll back changes to a previous known state whenever needed.

Check out this video about snapshots

For CTF competitions, a workflow I see quite a bit is:

1. Create a VM and tweak with all the tools you will need.
2. Snapshot the VM.
3. Start a challenge. This may require you to install new software, add new packages to Python, add temporary entries to /etc/hosts, download binaries for reverse engineering, etc.
4. Complete the challenge.
5. Rollback the VM to the pre-challenge snapshot. On to the next challenge!