Installation guide

on an automatic boot. With an automatic boot, the system begins the
initialization process and continues until completion or failure.
Manual intervention may be required if the automatic boot fails for
some reason, for example, if the fsck command fails.
In a manual boot, the system controls the initial operation, turns
control of the procedure over to you, then reinstates control to complete
the operation. When you boot the system to single-user mode, you are
relying on a manual boot. In an automatic or a manual boot, the
operation either succeeds or fails:
– If the boot operation succeeds, the system is initialized. In
single-user mode, the system displays the root prompt (#) on the
console or on the terminal screen. In multiuser mode, the system
displays the login prompt or a startup display. The prompt or
startup display differs according to hardware capability and
available startup software.
– If the boot operation fails, the system displays an error message
followed by a console firmware prompt (>>>). In the worst case, the
system hangs without displaying a console prompt.
• The system boots to either single-user or multiuser mode.
– In a boot to single-user mode, the software loads the kernel and
proceeds through the initialization tasks associated with process 0
(initialization) and process 1 (init). The init program creates a
Bourne shell (sh), turns control over to you, and waits for you to
exit from the shell with the exit command or Ctrl/d before
continuing with its startup tasks.
Because init does not invoke the startup script prior to turning
control over to you, the root file system is mounted read only,
startup of the network and other daemons does not occur, file
checking and correction are not enabled, and other operations
necessary for full system use are not automatically available to you.
Usually you boot to single-user mode to perform specific
administrative tasks that are best accomplished without the threat
of parallel activity by other users. You perform these tasks
manually before exiting from the Bourne shell. For example, you
might check new hardware, mount and check aberrant file systems,
change disk partitions, or set the system clock. When you finish
your work, you return control to the system, and init continues
with its startup tasks and boots to multiuser mode.
– In a boot to multiuser mode, the system loads the kernel and moves
through various phases such as hardware and virtual memory
initialization, resource allocation, scheduling, configuration, module
3–2 Starting Up and Shutting Down the System