Init

init (abbreviation of Initialization) is the program under Unix which launches all the other tasks. It is carried out like a data-processing demon and typically it has a Identifiant of process (PID) of 1.

The functionalities of the program init diverge considerably between BSD and System V.

The majority of the distributions Linux are compatible with the program init of Unix System V ; but there are exceptions : certain distributions as the Slackware use a program init which is close to that of Unix BSD others as the distribution Gentoo have a personalized program init . There are also several other alternative diagrams for this phase of initialization (for example, for Mac OS X 10.4 (TIGER), to also see the external references to the bottom of this page). The distribution Ubuntu (version 6.10) uses a task called Upstart instead of init , but this task in its current version (January 2007) is very close to the init System V.

With the boot

The Charger of starting load the Core Linux (and possible a Initrd), then the core assembles the Filing system root (the " /"), then it initializes the initial console. Then, it launches the first task: " init ".

The program init is at the same time the first task which the Linux core carries out when one Boot E a computer and the last task presents before the stop of the Ordinateur.

init of Unix BSD

With the Boot, the program init of Unix BSD carries out Shell S of initialization located in /etc/rc , then puts in place the various virtual terminals, text mode or graphic mode (X or other).

The large difference between the init of BSD and that of System V, it is that there is no levels of operation (runlevel) in Unix BSD. On these operating systems, in fact the files of /etc/rc determine how this initialization is carried out.

init of Unix System V

With the boot, the program init of Unix System V reads the file /etc/inittab , the field initdefault in this file determines which is the level of operation per defect. If this field is absent, the user must go on the console system to indicate manually which is the level of operation (Run level) selected.

The other lines of the file inittab indicate to the program init which are the tasks with launching and on which virtual terminal, according to the level of required operation.

To exceed the safety measures of Unix while avoiding passing by the task init

The program init is not the only option suggested when one boote a computer under Unix. On the majority of the chargers of starting (bootloader) modern (such LILO or GRUB), you can change the name of the program which is launched at the end of initialization by the core (by defect, it is /sbin/init ).

In general, this functionality is used to launch simple a Interpréteur of orders (HS, bash or Zsh, etc) in the place of the program init. It is enough, for example, to type init=/bin/sh with prompt of the charger of starting. That makes it possible a system administrator to correct the problems in certain extreme cases.

It is not even necessary to type a password. To mitigate this gap, it is possible to parameterize BIOS so that a password is required before the boot.

See too

Initng, a process of starting faster than init
Upstart of Ubuntu

External references

man page for init

alternative Diagrams for this phase of initialization :

boot-scripts
runit
svscan
minit

Random links: