NAME
init, telinit - process control initialization
SYNOPSIS
/sbin/init [0123456abcQqSs]
/etc/telinit [0123456abcQqSs]
AVAILABILITY
SUNWcsr
DESCRIPTION
init is a general process spawner. Its primary role is to
create processes from information stored in the file
/etc/inittab.
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. This sends
appropriate signals to the original init spawned by the
operating system at boot time, saying which run level to
invoke.
When the system is booted, init is invoked and the following
occurs. First, it reads /etc/default/init to set environ-
ment variables. This is typically where TZ (time zone) and
locale-related environments such as LANG or LC_CTYPE get
set.
init then looks in /etc/inittab for the initdefault entry
(see inittab(4)). If one exists, init usually uses the run
level specified in that entry as the initial run level to
enter. If there is no initdefault entry in /etc/inittab,
init asks the user to enter a run level from the virtual
system console. If an S or s is entered, init goes to the
single-user state. In this state, the virtual console ter-
minal is assigned to the user's terminal and is opened for
reading and writing. The command /sbin/su is invoked and a
message is generated on the physical console saying where
the virtual console has been relocated. 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.
If a 0 through 6 is entered, 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 init-
tab(4)). These entries are performed before any other pro-
cessing 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 descen-
dant 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.
New entries can be added to /etc/inittab at any time; how-
ever, 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 virtual console to
those modes saved in the file /etc/ioctl.syscon. This file
is written by init whenever the single-user state is
entered.
When a run level change request is made, init sends the
warning signal (SIGTERM) to all processes that are undefined
in the target run level. init waits five seconds before
forcibly terminating these processes by sending a kill sig-
nal (SIGKILL).
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/utmp and /var/adm/wtmp if it exists (see
who(1)). A history of the processes spawned is kept in
/var/adm/wtmp.
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.
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.
OPTIONS
0 Go into firmware.
1 Put the system in system administrator mode. All
file systems are mounted. Only a small set of
essential kernel processes are left running. This
mode is for administrative tasks such as instal-
ling optional utility packages. All files are
accessible and no users are logged in on the sys-
tem.
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.
3 Start the remote file sharing processes and dae-
mons. Mount and advertise remote resources. Run
level 3 extends multi-user mode and is known as
the remote-file-sharing state.
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 pos-
sible.
6 Stop the operating system and reboot to the state
defined by the initdefault entry in /etc/inittab.
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 com-
mands, but which do not cause the current run
level to change.
Q, q Re-examine /etc/inittab.
S, s Enter single-user mode. When this occurs, the
terminal which executed this command becomes the
system console. This is the only run level that
doesn't require the existence of a properly for-
matted /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
the system comes up to S or s, file systems for
users' files are not mounted and only essential
kernel processes are running. When the system
comes down to S or s, all mounted file systems
remain mounted, and all processes started by init
that should only be running in multi-user mode are
killed. In addition, any process that has a utmp
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 mon-
itors, including ttymon login services, are
killed. Other processes not started directly by
init will remain running. For example, cron
remains running.
FILES
/etc/inittab controls process dispatching by init
/var/adm/utmp accounting information
/var/adm/wtmp history of all logins since file was
last created
/etc/ioctl.syscon
/dev/console system console device
/etc/default/init environment variables.
Default values can be set for the fol-
lowing flags in /etc/default/init. For
example: TZ=US/Pacific
TZ Either specifies the
timezone information
(see ctime(3C)) or
the name of a
timezone information
file
/usr/share/lib/zoneinfo.
LC_CTYPE Character character-
ization 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 partic-
ular LC_* is also
not set, the value
of LANG is used for
that particular
environmental vari-
able.
SEE ALSO
login(1), sh(1), stty(1), who(1), shutdown(1M), ttymon(1M),
kill(2), ctime(3C), inittab(4), utmp(4), utmpx(4), termio(7)
DIAGNOSTICS
If init finds that it is respawning an entry from
/etc/inittab more than ten times in two minutes, assumes
that there is an error in the command string in the entry,
and generates an error message on the system console. It
will then refuse to respawn this entry until either five
minutes has elapsed or it receives a signal from a user-
spawned init or telinit. 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.
When attempting to boot the system, failure of init to
prompt for a new run level may be caused by the virtual sys-
tem console being linked to a device other than the physical
system console.
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 sys-
tem will loop by going to firmware and rebooting continu-
ously.
If the utmp 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.