init(1m) DG/UX 4.30 init(1m)
NAME
init, telinit - process control initialization
SYNOPSIS
/etc/init [0123456SsQqabc]
/etc/telinit [0123456SsQqabc]
DESCRIPTION
Init
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
are 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 /etc/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.
S Single User
A single user run state that is a safe state to
which the system can always be booted, assuming
the root (/) filesystem is intact. The root
filesystem is mounted, and the init and su
processes are running on the console.
0 Halt
A shutdown state where the system is shut down so
it is safe to halt the processor(s).
1 Admin
A limited user run state used for administrative
purposes without users on the system. The / and
/usr filesystems are mounted, the update daemon is
running, and getty processes are spawned on the
console and administrative terminals.
2 Multi-user, Network Connected
A multi-user run state which allows users to log
in and make use of all system services and some
network services. The system is connected to the
network and can access other hosts, but this
system's network services are not available to
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other hosts. Besides the services made available
in run state 1, all local filesystems are mounted,
various system service daemons like cron, lp, and
acct are started, all user terminal getty
processes are spawned, the network transport layer
is started, and yp lookup services are started.
3 Multi-user, Full Network
A multi-user run state that allows users to log in
and make full use of all system and network
services. Besides the services made available in
run state 2, all network daemons and services are
started. Remote mounted filesystems are mounted.
4 Customer Defined
A multi-user run state to be defined as an
alternate site-specific environment by the
customer. Not necessary for system operation.
5,6 Not currently defined.
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.
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
Next, init looks in /etc/inittab for the initdefault entry
(see inittab(4)). If there is one, init 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
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,
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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
/bin/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.
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.
In a multi-user environment, /etc/inittab is set up so that
init will create a getty process for each terminal that the
administrator sets up to respawn.
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.
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init(1m) DG/UX 4.30 init(1m)
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 5 seconds before
forcibly terminating these processes via the kill signal
(SIGKILL).
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.
telinit
telinit, which is linked to /etc/init, is used to direct the
actions of init. It takes a one-character argument and
signals init to take the appropriate action. telinit is the
AT&T version of BSD's init.
FILES
/etc/inittab
/etc/utmp
/etc/wtmp
/etc/ioctl.syscon
/dev/console
/dev/contty
SEE ALSO
getty(1M), shutdown(1M), gettydefs(4), inittab(4), utmp(4),
termio(7).
login(1), sh(1), stty(1), who(1) telinit(1M)
kill(2)
DIAGNOSTICS
If init finds that it is respawning an entry from
/etc/inittab more than 10 times in 2 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 5
minutes has elapsed or it receives a signal from a user-
spawned init (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.
WARNINGS
init and telinit can be run only by someone who is super-
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init(1m) DG/UX 4.30 init(1m)
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.
The change to /etc/gettydefs described in the WARNINGS
section of the gettydefs(4) manual page will permit
terminals to pass 8 bits to the system as long as the system
is in multi-user state (run level greater than 1). When the
system changes to single-user state, the getty is killed and
the terminal attributes are lost. To permit a terminal to
pass 8 bits to the system in single-user state, after you
are in single-user state, type: stty -istrip cs8 .
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