Contrary to open-source folklore, it is mostly paid developers who are building the Linux kernel.
Kernel development follows a time-based release model with a new release occurring every two to three months. This is designed to help speed the development for all Linux distributions so that each one doesn’t need to make kernel-specific updates or changes. More than 6,100 individual developers from more 600 different companies have contributed to the kernel since 2005, according the report.
