A fork bomb from the Linux shell

. (){ .|.  &};. Or:() {:|:&};:

These 13 characters by Jaromil, in 2002 designed the most streamlined implementation of a fork bomb.

. () Note the following to define a function, the function name is a decimal point, no optional parameters;
{denotes the beginning of the function body;
.|. & represents what the function body really wants to do, first it recursively uses this function, and then Li Yonggui the pipeline to invoke a new process (the thing it does is to call this function recursively) and put it in the background.
} Indicates the end of the function body;
; Does not perform any operations that are used to separate two commands from the command line. Overall, it shows that the program consists of two parts, first defining a function, and then invoking the function;
. Represents the call to this function.

This recursive function can call itself, constantly generate new processes, resulting in a denial of service attack, the function called the former & the child process into the background. This dangerous code will branch out a lot of processes and is called a fork bomb.

You can avoid this bomb by modifying the configuration file/etc/security/limits.conf to limit the maximum number of processes that can be generated.