You can easily limit the amount of processes that can be spawned in Ubuntu and most other Linux distributions by modifying
Then add this line to the bottom of that file:
* hard nproc nnn
The above command will list all processes for all users including threads, sum them up and list the user name with the largest amount of processes. To be on the safe side, open as many applications as you normally need before running the above command and then double that number for safety.
After this limit is put into place, you'll need to reboot, but it will affect each user on the system. So if a fork bomb is executed as any user (root included) it'll have that hard limit.
If you're not looking to restart any time soon, you can use
sudo ulimit -u 800 which will place the restriction only on the running session but can be easily circumvented by a fork bomb with
After restart, whatever is in
/etc/security/limits.conf will then be used.
Some additional information about fork bombs: They aren't malware or anything dreadful. They typically consist of something as basic as a script that calls itself twice - thereby growing its presence on the machine exponentially. Even though they have a small memory footprint given the rapid pace they multiple they quickly fill all available RAM and the machine freezes or reboots. The only danger is loosing unsaved information. I would classify a forkbomb much more as a prank than malicious software.
An important reminder:
You should rarely ever execute anything in command line when you aren't 98% certain of its action. If you can't read the commands you're executing - don't do it. This applies double to unreadable chunks of hex/base64 characters, which can be used to obscure all sorts of nastiness. If you're uncertain of a command you can always search for it's actions in the Ubuntu Manpages and be extra cautions when using
sudo since that will execute as the root user.