init process
1、它有着多种实现,在 Operating-system-service-management
章节对这些implementation进行说明
wikipedia init
In Unix-based computer operating systems, init (short for initialization) is the first process started during booting of the computer system.
Init is a daemon process that continues running until the system is shut down.
It is the direct or indirect ancestor of all other processes and automatically adopts all orphaned processes.
NOTE: 1、它会收养"all orphaned processes",
Init is started by the kernel during the booting process; a kernel panic will occur if the kernel is unable to start it. Init is typically assigned process identifier 1.