illumos: 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)