init.1m (2010 09)
i
init(1M) init(1M)
NAME
init - process control initialization
SYNOPSIS
/sbin/init [012
3456SsQqa
bc]
DESCRIPTION
The
init daemon and command is a general process spawner. Its primary role is to create processes
from a script stored in the file
/etc/inittab (see inittab (4)). This file usually has init spawn a
getty on each line where users can log in. It also controls autonomous processes required by any partic-
ular system.
At boot time,
init is started as a system daemon.
While the system is running, a user-spawned
init directs the actions of the boot init. It accepts a
one-character argument and signals the boot
init with the kill() system call to perform the appropri-
ate action.
The arguments have the following effect:
0−6 Place the system in one of the run levels
0 through 6.
abc Process the inittab entries that have the special "run level"
a, b,orc, without chang-
ing the numeric run level.
Qq Re-examine the inittab entries without changing the run level.
Ss Enter the single-user environment. When this level change occurs, the logical system
console
/dev/syscon is changed to the terminal from which the command was exe-
cuted.
Boot
init considers the system to be in a run level at any given time. A run level can be viewed as a
software configuration of the system, where each configuration allows only a selected group of processes
to exist. The processes spawned by boot init for each of these run levels are defined in the
inittab
file. Boot init can be in one of eight run levels, 0−6, and
S or s. The run level is changed by having a
privileged user run the
init command. This user-spawned init sends appropriate signals to the boot
init.
Boot
init is invoked inside the HP-UX system as the last step in the boot procedure. Boot
init first
performs any required machine-dependent initialization, such as setting the system context. Next, boot
init looks for the inittab file to see if there is an entry of the type
initdefault (see inittab (4)). If
an
initdefault entry is found, boot init uses the run level specified in that entry as the initial run
level to enter. If this entry is not in inittab,orinittab is not found, boot
init requests that the
user enter a run level from the logical system console,
/dev/syscon.IfS or s
is entered, boot init
goes into the single-user level. This is the only run level that does not require the existence of a prop-
erly formatted inittab file. If inittab does not exist, then by default the only legal run level that
boot init can enter is the single-user level.
In the single-user level, the logical system console terminal
/dev/syscon is opened for reading and
writing, and the command /usr/bin/su, /usr/bin/sh,or/sbin/sh is invoked immediately. To
exit from the single-user run level, one of two options can be selected:
• If the shell is terminated with an end-of-file, boot
init reprompts for a new run level.
• User
init can signal boot init and force it to change the current system run level.
When attempting to boot the system, some processes spawned by boot
init may send display messages
to the system console (depending on the contents of inittab). If messages are expected but do not
appear during booting, it may be caused by the logical system console (/dev/syscon) being linked to a
device that is not the physical system console (/dev/systty). If this occurs, you can force boot init to
relink /dev/syscon to /dev/systty by pressing the DEL (delete) key (ASCII 127) on the physical
system console.
When boot
init prompts for the new run level, you can only enter one of the digits 0 through 6 or the
letter S or s. If you enter S, boot init operates as previously described in single-user mode with the
additional result that /dev/syscon is linked to the user’s terminal line, thus making it the logical sys-
tem console. A message is generated on the physical system console, /dev/systty, identifying the new
logical system console.
HP-UX 11i Version 3: September 2010 − 1 − Hewlett-Packard Company 1