When these preparatory activities have been completed, the kernel creates another process that will run the Process 0, if it exists, is really part of the kernel itself.
Process 0 is often the scheduler (controls which processes execute at what time under BSD) or the swapper (moves process memory pages to and from swap space under System V).
However, some systems assign PID 0 to a different process, and others do not have a process 0 at all.
), you might wonder how either one can be running before the corresponding filesystem has been checked.
The boot program is stored in a standard location on a bootable device.
For a normal boot from disk, for example, the boot program might be located in block 0 of the root disk or, less commonly, in a special partition on the root disk.
The system administrator must then take whatever steps are necessary to resolve the problem.
Once this is done, booting may continue to multiuser mode by entering CTRL-D, terminating the single-user mode shell: . Single-user mode represents a minimal system startup. Urizen Ur-Unix 9.1 on hamlet The hostname is hamlet. and clearing /tmp, for instancebut we've retained them for nostalgia's sake.Another situation in which the system might enter single-user mode automatically occurs if there are any problems in the boot process that the system cannot handle on its own.Examples of such circumstances include filesystem problems that cannot fix in its default mode and errors in one of the system initialization files.These files are organized very differently under System V and BSD, but they accomplish the same purposes.They are described in detail later in this chapter.Other systems use different boot programs depending on the type of boot. When the power comes on or the system is reset, the BIOS starts the master boot program, located in the first 512 bytes of the system disk.