286 lines
4.8 KiB
HTML
286 lines
4.8 KiB
HTML
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
|
|
<HTML
|
|
><HEAD
|
|
><TITLE
|
|
>init comes first</TITLE
|
|
><META
|
|
NAME="GENERATOR"
|
|
CONTENT="Modular DocBook HTML Stylesheet Version 1.7"><LINK
|
|
REL="HOME"
|
|
TITLE="Linux System Administrators Guide"
|
|
HREF="index.html"><LINK
|
|
REL="UP"
|
|
TITLE="init"
|
|
HREF="init-intro.html"><LINK
|
|
REL="PREVIOUS"
|
|
TITLE="init"
|
|
HREF="init-intro.html"><LINK
|
|
REL="NEXT"
|
|
TITLE="Configuring init to start
|
|
getty: the
|
|
/etc/inittab file"
|
|
HREF="config-init.html"></HEAD
|
|
><BODY
|
|
CLASS="SECT1"
|
|
BGCOLOR="#FFFFFF"
|
|
TEXT="#000000"
|
|
LINK="#0000FF"
|
|
VLINK="#840084"
|
|
ALINK="#0000FF"
|
|
><DIV
|
|
CLASS="NAVHEADER"
|
|
><TABLE
|
|
SUMMARY="Header navigation table"
|
|
WIDTH="100%"
|
|
BORDER="0"
|
|
CELLPADDING="0"
|
|
CELLSPACING="0"
|
|
><TR
|
|
><TH
|
|
COLSPAN="3"
|
|
ALIGN="center"
|
|
>Linux System Administrators Guide: </TH
|
|
></TR
|
|
><TR
|
|
><TD
|
|
WIDTH="10%"
|
|
ALIGN="left"
|
|
VALIGN="bottom"
|
|
><A
|
|
HREF="init-intro.html"
|
|
ACCESSKEY="P"
|
|
>Prev</A
|
|
></TD
|
|
><TD
|
|
WIDTH="80%"
|
|
ALIGN="center"
|
|
VALIGN="bottom"
|
|
>Chapter 9. <B
|
|
CLASS="COMMAND"
|
|
>init</B
|
|
></TD
|
|
><TD
|
|
WIDTH="10%"
|
|
ALIGN="right"
|
|
VALIGN="bottom"
|
|
><A
|
|
HREF="config-init.html"
|
|
ACCESSKEY="N"
|
|
>Next</A
|
|
></TD
|
|
></TR
|
|
></TABLE
|
|
><HR
|
|
ALIGN="LEFT"
|
|
WIDTH="100%"></DIV
|
|
><DIV
|
|
CLASS="SECT1"
|
|
><H1
|
|
CLASS="SECT1"
|
|
><A
|
|
NAME="INIT-PROCESS"
|
|
></A
|
|
>9.1. <B
|
|
CLASS="COMMAND"
|
|
>init</B
|
|
> comes first</H1
|
|
><P
|
|
><B
|
|
CLASS="COMMAND"
|
|
>init</B
|
|
> is one of those programs that
|
|
are absolutely essential to the operation of a Linux system,
|
|
but that you still can mostly ignore. A good Linux distribution
|
|
will come with a configuration for <B
|
|
CLASS="COMMAND"
|
|
>init</B
|
|
>
|
|
that will work for most systems, and on these systems there is
|
|
nothing you need to do about <B
|
|
CLASS="COMMAND"
|
|
>init</B
|
|
>. Usually,
|
|
you only need to worry about <B
|
|
CLASS="COMMAND"
|
|
>init</B
|
|
> if you hook
|
|
up serial terminals, dial-in (not dial-out) modems, or if you
|
|
want to change the default run level.</P
|
|
><P
|
|
>When the kernel has started itself (has been loaded
|
|
into memory, has started running, and has initialized all
|
|
device drivers and data structures and such), it finishes its
|
|
own part of the boot process by starting a user level program,
|
|
<B
|
|
CLASS="COMMAND"
|
|
>init</B
|
|
>. Thus, <B
|
|
CLASS="COMMAND"
|
|
>init</B
|
|
> is always
|
|
the first process (its process number is always 1).</P
|
|
><P
|
|
>The kernel looks for <B
|
|
CLASS="COMMAND"
|
|
>init</B
|
|
>
|
|
in a few locations that have been historically used
|
|
for it, but the proper location for it (on a Linux
|
|
system) is <TT
|
|
CLASS="FILENAME"
|
|
>/sbin/init</TT
|
|
>. If the
|
|
kernel can't find <B
|
|
CLASS="COMMAND"
|
|
>init</B
|
|
>, it tries to run
|
|
<TT
|
|
CLASS="FILENAME"
|
|
>/bin/sh</TT
|
|
>, and if that also fails, the startup
|
|
of the system fails.</P
|
|
><P
|
|
>When <B
|
|
CLASS="COMMAND"
|
|
>init</B
|
|
> starts, it finishes the
|
|
boot process by doing a number of administrative tasks, such
|
|
as checking filesystems, cleaning up <TT
|
|
CLASS="FILENAME"
|
|
>/tmp</TT
|
|
>,
|
|
starting various services, and starting a <B
|
|
CLASS="COMMAND"
|
|
>getty</B
|
|
>
|
|
for each terminal and virtual console where users should be able
|
|
to log in (see <A
|
|
HREF="log-in-and-out.html"
|
|
>Chapter 10</A
|
|
>).</P
|
|
><P
|
|
>After the system is properly up, <B
|
|
CLASS="COMMAND"
|
|
>init</B
|
|
>
|
|
restarts <B
|
|
CLASS="COMMAND"
|
|
>getty</B
|
|
> for each terminal
|
|
after a user has logged out (so that the next user can log
|
|
in). <B
|
|
CLASS="COMMAND"
|
|
>init</B
|
|
> also adopts orphan processes: when
|
|
a process starts a child process and dies before its child, the
|
|
child immediately becomes a child of <B
|
|
CLASS="COMMAND"
|
|
>init</B
|
|
>.
|
|
This is important for various technical reasons, but it is good
|
|
to know it, since it makes it easier to understand process lists
|
|
and process tree graphs.
|
|
There are a few variants of <B
|
|
CLASS="COMMAND"
|
|
>init</B
|
|
>
|
|
available. Most Linux distributions
|
|
use <B
|
|
CLASS="COMMAND"
|
|
>sysvinit</B
|
|
> (written by Miquel
|
|
van Smoorenburg), which is based on the System V
|
|
<B
|
|
CLASS="COMMAND"
|
|
>init</B
|
|
> design. The BSD versions of Unix have
|
|
a different <B
|
|
CLASS="COMMAND"
|
|
>init</B
|
|
>. The primary difference
|
|
is run levels: System V has them, BSD does not (at least
|
|
traditionally). This difference is not essential. We'll look
|
|
at <B
|
|
CLASS="COMMAND"
|
|
>sysvinit</B
|
|
> only. </P
|
|
></DIV
|
|
><DIV
|
|
CLASS="NAVFOOTER"
|
|
><HR
|
|
ALIGN="LEFT"
|
|
WIDTH="100%"><TABLE
|
|
SUMMARY="Footer navigation table"
|
|
WIDTH="100%"
|
|
BORDER="0"
|
|
CELLPADDING="0"
|
|
CELLSPACING="0"
|
|
><TR
|
|
><TD
|
|
WIDTH="33%"
|
|
ALIGN="left"
|
|
VALIGN="top"
|
|
><A
|
|
HREF="init-intro.html"
|
|
ACCESSKEY="P"
|
|
>Prev</A
|
|
></TD
|
|
><TD
|
|
WIDTH="34%"
|
|
ALIGN="center"
|
|
VALIGN="top"
|
|
><A
|
|
HREF="index.html"
|
|
ACCESSKEY="H"
|
|
>Home</A
|
|
></TD
|
|
><TD
|
|
WIDTH="33%"
|
|
ALIGN="right"
|
|
VALIGN="top"
|
|
><A
|
|
HREF="config-init.html"
|
|
ACCESSKEY="N"
|
|
>Next</A
|
|
></TD
|
|
></TR
|
|
><TR
|
|
><TD
|
|
WIDTH="33%"
|
|
ALIGN="left"
|
|
VALIGN="top"
|
|
><B
|
|
CLASS="COMMAND"
|
|
>init</B
|
|
></TD
|
|
><TD
|
|
WIDTH="34%"
|
|
ALIGN="center"
|
|
VALIGN="top"
|
|
><A
|
|
HREF="init-intro.html"
|
|
ACCESSKEY="U"
|
|
>Up</A
|
|
></TD
|
|
><TD
|
|
WIDTH="33%"
|
|
ALIGN="right"
|
|
VALIGN="top"
|
|
>Configuring <B
|
|
CLASS="COMMAND"
|
|
>init</B
|
|
> to start
|
|
<B
|
|
CLASS="COMMAND"
|
|
>getty</B
|
|
>: the
|
|
<TT
|
|
CLASS="FILENAME"
|
|
>/etc/inittab</TT
|
|
> file</TD
|
|
></TR
|
|
></TABLE
|
|
></DIV
|
|
></BODY
|
|
></HTML
|
|
> |