init(1M) DG/UX 5.4.2 init(1M)
NAME
init, telinit - process control initialization
SYNOPSIS
/sbin/init [0i123456SsQqabc]
/sbin/telinit [0i123456SsQqabc]
DESCRIPTION
init is a general process spawner. Its primary role is to create
processes from information stored in the file /etc/inittab [see
inittab(4)].
At any given time, the system is in one of eight possible run levels.
A run level is a software configuration of the system under which
only a selected group of processes exist. The processes spawned by
init for each of these run levels is defined in /etc/inittab. init
can be in one of eight run levels, 0-6 and S or s (run levels S and s
are identical). The run level changes when a privileged user runs
/sbin/init. This user-spawned init sends appropriate signals to the
original init spawned by the operating system when the system was
booted, telling it which run level to change to.
The following are the arguments to init.
0 shut the machine down so it is safe to remove the
power. Have the machine remove power if it can.
i put the system in installation mode. All local file
systems are mounted and a small set of essential kernel
processes are running. The installman(1M) program is
invoked to perform initial installation steps.
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 installing optional
utility packages. All files are accessible and no
users are logged in on the system.
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 daemons.
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.
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5 Stop the system and go to the firmware monitor.
Bringing the system to this state is functionally
equivalent to bringing it to init state s then entering
the halt(1M) command.
6 Stop the system and reboot to the state defined by the
initdefault entry in /etc/inittab. Bringing the system
to this state is functionally equivalent to bringing it
to init state s then entering the reboot(1M) command.
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. These
pseudo-levels are not executed at run level S. That
are only executed at level 1 or higher.
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 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 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 monitors, including ttymon login
services, are killed. Other processes not started
directly by init will remain running. For example,
cron remains running.
When a DG/UX system is booted, init is invoked and the following
occurs. First, init attempts to fsck and mount /usr using the /usr
entry in /etc/fstab. If there is no /etc/fstab but there is an
/etc/fstab.proto, init copies /etc/fstab.proto to /etc/fstab and then
attempts the mount operation. The sequence is equivalent to:
if [ ! -f /etc/fstab ] &&
[ -f /etc/fstab.proto ]
then
cp /etc/fstab.proto /etc/fstab
fi
mount -f /
fsck -xq /usr
mount /usr
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Next, init looks in /etc/inittab for the initdefault entry [see
inittab(4)]. If there is one, init will usually use the run level
specified in that entry as the initial run level to enter. If there
is no initdefault entry in /etc/inittab, init requests that the user
enter a run level from the virtual system console. If an S or s is
entered, init goes to the single-user state. If /usr was not mounted
successfully, then single-user state is entered regardless of the
initdefault setting in inittab. In the single-user state the virtual
console terminal 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 signal init to
change the run level of the system. Note that if the shell is
terminated (via an end-of-file), init will only re-initialize to the
single-user state if the /etc/inittab file does not exist.
If a 0 through 6 is entered, init enters the corresponding run level
if /usr is mounted. init will not permit a state change if /usr is
not mounted. 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(4)]. 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. 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 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 via the kill signal (SIGKILL).
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The shell running on each terminal will terminate when the user types
an end-of-file or hangs up. When init receives a signal telling it
that a process it spawned has died, it records the fact and the
reason it died in /etc/utmp and /etc/wtmp if it exists [see who(1)].
A history of the processes spawned is kept in /etc/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, 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.
FILES
/etc/inittab
/etc/utmp
/etc/wtmp
/etc/ioctl.syscon
/dev/console
SEE ALSO
installman(1M), ttymon(1M), shutdown(1M), inittab(4), utmp(4),
termio(7).
login(1), sh(1), stty(1), who(1).
kill(2).
DIAGNOSTICS
If init finds that it is respawning an entry from /etc/inittab more
than ten times in two minutes, it will assume that there is an error
in the command string in the entry, and generate 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 because the virtual system console is 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 the
/etc/inittab file. A good rule to follow when modifying this file is
to avoid adding this state to any line other than the initdefault.
If a default state is not specified in the initdefault entry in
/etc/inittab, state ``s'' is entered.
If the utmp file cannot be created when booting the system, the
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system will boot to state ``s'' regardless of the state specified in
the initdefault entry in /etc/inittab. This can happen if the root
filesystem is not accessible.
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