Tribblix: manual page: init.8

INIT(8) Maintenance Commands and Procedures INIT(8)

NAME

init, telinit - process control initialization

SYNOPSIS

/sbin/init [0123456abcQqSs]

/etc/telinit [0123456abcQqSs]

DESCRIPTION

init is the default primordial user process. (Options given to the
kernel during boot may result in the invocation of an alternative
primordial user process, as described on kernel(8)). init initiates
the core components of the service management facility,
svc.configd(8) and svc.startd(8), and restarts these components if
they fail. For backwards compatibility, init also starts and restarts
general processes according to /etc/inittab, as desribed below.

The run levels and system booting descriptions given below are
provided for compatibility purposes only, and otherwise made obsolete
by the service management facility, smf(7).

init Failure
If init exits for any reason other than system shutdown, it will be
restarted with process-ID 1.

Run Level Defined

At any given time, the system is in one of eight possible run levels.
A run level is a software configuration under which only a selected
group of processes exists. Processes spawned by init for each of
these run levels are defined in /etc/inittab. init can be in one of
eight run levels, 0-6 and S or s (S and s are identical). The run
level changes when a privileged user runs /sbin/init.

init and System Booting
When the system is booted, init is invoked and the following occurs.
First, it reads /etc/default/init to set environment variables. This
is typically where TZ (time zone) and locale-related environments
such as LANG or LC_CTYPE get set. (See the FILES section at the end
of this page.) init then looks in /etc/inittab for the initdefault
entry (see inittab(5)). If the initdefault entry:

exists

init usually uses the run level specified in that entry as the
initial run level to enter only if the options/milestone property
has not been specified for svc.startd(8).

does not exist

The service management facility, smf(7), examines its
configuration specified in svc.startd(8), and enters the
milestone specified by the options/milestone property.

The initdefault entry in /etc/inittab corresponds to the following
run levels:

S or s

init goes to the single-user state. In this state, the system
console device (/dev/console) is opened for reading and writing
and the command /sbin/su, (see su(8)), is invoked. Use either
init or telinit to change the run level of the system. Note that
if the shell is terminated (using an end-of-file), init only re-
initializes to the single-user state if /etc/inittab does not
exist.

0-6

init enters the corresponding run level. Run levels 0, 5, and 6
are reserved states for shutting the system down. Run levels 2,
3, and 4 are available as multi-user operating states.

If this is the first time since power up that init has entered a run
level other than single-user state, init first scans /etc/inittab for
boot and bootwait entries (see inittab(5)). These entries are
performed before any other processing of /etc/inittab takes place,
providing that the run level entered matches that of the entry. In
this way any special initialization of the operating system, such as
mounting file systems, can take place before users are allowed onto
the system. init then scans /etc/inittab and executes all other
entries that are to be processed for that run level.

To spawn each process in /etc/inittab, init reads each entry and for
each entry that should be respawned, it forks a child process. After
it has spawned all of the processes specified by /etc/inittab, init
waits for one of its descendant processes to die, a powerfail signal,
or a signal from another init or telinit process to change the
system's run level. When one of these conditions occurs, init re-
examines /etc/inittab.

inittab Additions
New entries can be added to /etc/inittab at any time; however, init
still waits for one of the above three conditions to occur before re-
examining /etc/inittab. To get around this, init Q or init q command
wakes init to re-examine /etc/inittab immediately.

When init comes up at boot time and whenever the system changes from
the single-user state to another run state, init sets the ioctl(2)
states of the console to those modes saved in the file
/etc/ioctl.syscon. init writes this file whenever the single-user
state is entered.

Run Level Changes

When a run level change request is made, init or a designate sends
the warning signal (SIGTERM) to all processes that are undefined in
the target run level. A minimum interval of five seconds is observed
before init or its designate forcibly terminates these processes by
sending a kill signal (SIGKILL). Additionally, init informs
svc.startd(8) that the run level is changing. svc.startd(8) then
restricts the system to the set of services which the milestone
corresponding to the run-level change depends on.

When init receives a signal telling it that a process it spawned has
died, it records the fact and the reason it died in /var/adm/utmpx
and /var/adm/wtmpx if it exists (see who(1)). A history of the
processes spawned is kept in /var/adm/wtmpx.

If init receives a powerfail signal (SIGPWR) it scans /etc/inittab
for special entries of the type powerfail and powerwait. These
entries are invoked (if the run levels permit) before any further
processing takes place. In this way init can perform various cleanup
and recording functions during the powerdown of the operating system.

Environment Variables in /etc/default/init
You can set default values for environment variables, for such items
as timezone and character formatting, in /etc/default/init. See the
FILES section, below, for a list of these variables.

telinit
telinit, which is linked to /sbin/init, is used to direct the actions
of init. It takes a one-character argument and signals init to take
the appropriate action.

SECURITY

init uses pam(3PAM) for session management. The PAM configuration
policy, listed through /etc/pam.conf, specifies the session
management module to be used for init. Here is a partial pam.conf
file with entries for init using the UNIX session management module.

init session required pam_unix_session.so.1

If there are no entries for the init service, then the entries for
the "other" service will be used.

OPTIONS

0

Go into firmware.

1

Put the system in system administrator mode. All local file
systems are mounted. Only a small set of essential kernel
processes are left running. This mode is for administrative tasks
such as installing optional utility packages. All files are
accessible and no users are logged in on the system.

This request corresponds to a request for smf(7) to restrict the
system milestone to svc:/milestone/single-user:default.

2

Put the system in multi-user mode. All multi-user environment
terminal processes and daemons are spawned. This state is
commonly referred to as the multi-user state.

This request corresponds to a request for smf(7) to restrict the
system milestone to svc:/milestone/multi-user:default.

3

Extend multi-user mode by making local resources available over
the network.

This request corresponds to a request for smf(7) to restrict the
system milestone to svc:/milestone/multi-user-server:default.

4

Is available to be defined as an alternative multi-user
environment configuration. It is not necessary for system
operation and is usually not used.

5

Shut the machine down so that it is safe to remove the power.
Have the machine remove power, if possible.

6

Stop the operating system and reboot to the state defined by the
initdefault entry in /etc/inittab.

On x86 systems, service svc:/system/boot-config:default is
enabled by default. When the config/fastreboot_default property
is set to true, init 6 will bypass the firmware.

a,b,c

Process only those /etc/inittab entries having the a, b, or c run
level set. These are pseudo-states, which may be defined to run
certain commands, but which do not cause the current run level to
change.

Q,q

Re-examine /etc/inittab.

S, s

Enter single-user mode. This is the only run level that doesn't
require the existence of a properly formatted /etc/inittab file.
If this file does not exist, then by default, the only legal run
level that init can enter is the single-user mode. When in
single-user mode, the filesystems required for basic system
operation will be mounted. When the system comes down to single-
user mode, these file systems will remain mounted (even if
provided by a remote file server), and any other local
filesystems will also be left mounted. During the transition
down to single-user mode, all processes started by init or init.d
scripts that should only be running in multi-user mode are
killed. In addition, any process that has a utmpx entry will be
killed. This last condition insures that all port monitors
started by the SAC are killed and all services started by these
port monitors, including ttymon login services, are killed.

This request corresponds to a request for smf(7) to restrict the
system milestone to svc:/milestone/single-user:default.

FILES

/dev/console

System console device.

/etc/default/init

Contains environment variables and their default values. For
example, for the timezone variable, TZ, you might specify
TZ=US/Pacific. The variables are:

TZ

Either specifies the timezone information (see ctime(3C)) or
the name of a timezone information file
/usr/share/lib/zoneinfo.

Refer to the TIMEZONE(5) man page before changing this
setting.

CMASK

The mask (see umask(1)) that init uses and that every process
inherits from the init process. If not set, init uses the
mask it inherits from the kernel. Note that init always
attempts to apply a umask of 022 before creating a file,
regardless of the setting of CMASK

LC_CTYPE

Character characterization information

LC_MESSAGES

Message translation

LC_MONETARY

Monetary formatting information

LC_NUMERIC

Numeric formatting information

LC_TIME

Time formatting information

LC_ALL

If set, all other LC_* environmental variables take-on this
value.

LANG

If LC_ALL is not set, and any particular LC_* is also not
set, the value of LANG is used for that particular
environmental variable.

/etc/inittab

Controls process dispatching by init.

/etc/ioctl.syscon

ioctl states of the console, as saved by init when single-user
state is entered.

/etc/svc/volatile/init.state

init state necessary to recover from failure.

/var/adm/utmpx

User access and administration information.

/var/adm/wtmpx

History of user access and administration information.

/var/run/initpipe

A named pipe used for internal communication.

DIAGNOSTICS

If init finds that it is respawning an entry from /etc/inittab more
than ten times in two minutes, it assumes that there is an error in
the command string in the entry and generates an error message on the
system console. It then refuses to respawn this entry until either
five minutes has elapsed or it receives a signal from a user-spawned
init or telinit command. This prevents init from eating up system
resources when someone makes a typographical error in the inittab
file, or a program is removed that is referenced in /etc/inittab.

NOTES

init and telinit can be run only by a privileged user.

The S or s state must not be used indiscriminately in /etc/inittab.
When modifying this file, it is best to avoid adding this state to
any line other than initdefault.

If a default state is not specified in the initdefault entry in
/etc/inittab, state 6 is entered. Consequently, the system will loop
by going to firmware and rebooting continuously.

If the utmpx file cannot be created when booting the system, the
system will boot to state "s" regardless of the state specified in
the initdefault entry in /etc/inittab. This can occur if the /var
file system is not accessible.

When a system transitions down to the S or s state, the /etc/nologin
file (see nologin(5)) is created. Upon subsequent transition to run
level 2, this file is removed.

init uses /var/run/initpipe, a named pipe, for internal
communication.

The pam_unix(7) module is no longer supported. Similar functionality
is provided by pam_unix_session(7).

September 2, 2009 INIT(8)