387 lines
5.8 KiB
HTML
387 lines
5.8 KiB
HTML
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
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<HTML
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><HEAD
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><TITLE
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>Configuring init to start
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getty: the
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/etc/inittab file</TITLE
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><META
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NAME="GENERATOR"
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CONTENT="Modular DocBook HTML Stylesheet Version 1.7"><LINK
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REL="HOME"
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TITLE="Linux System Administrators Guide"
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HREF="index.html"><LINK
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REL="UP"
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TITLE="init"
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HREF="init-intro.html"><LINK
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REL="PREVIOUS"
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TITLE="init comes first"
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HREF="init-process.html"><LINK
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REL="NEXT"
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TITLE="Run levels"
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HREF="run-levels-intro.html"></HEAD
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><BODY
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CLASS="SECT1"
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BGCOLOR="#FFFFFF"
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TEXT="#000000"
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LINK="#0000FF"
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VLINK="#840084"
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ALINK="#0000FF"
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><DIV
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CLASS="NAVHEADER"
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><TABLE
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SUMMARY="Header navigation table"
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WIDTH="100%"
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BORDER="0"
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CELLSPACING="0"
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><TR
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><TH
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COLSPAN="3"
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ALIGN="center"
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>Linux System Administrators Guide: </TH
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></TR
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><TR
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><TD
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WIDTH="10%"
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ALIGN="left"
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VALIGN="bottom"
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><A
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HREF="init-process.html"
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ACCESSKEY="P"
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>Prev</A
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></TD
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><TD
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WIDTH="80%"
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ALIGN="center"
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VALIGN="bottom"
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>Chapter 9. <B
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CLASS="COMMAND"
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>init</B
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></TD
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><TD
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WIDTH="10%"
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ALIGN="right"
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VALIGN="bottom"
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><A
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HREF="run-levels-intro.html"
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ACCESSKEY="N"
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>Next</A
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></TD
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></TR
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></TABLE
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><HR
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ALIGN="LEFT"
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WIDTH="100%"></DIV
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><DIV
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CLASS="SECT1"
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><H1
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CLASS="SECT1"
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><A
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NAME="CONFIG-INIT"
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></A
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>9.2. Configuring <B
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CLASS="COMMAND"
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>init</B
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> to start
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<B
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CLASS="COMMAND"
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>getty</B
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>: the
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<TT
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CLASS="FILENAME"
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>/etc/inittab</TT
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> file</H1
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><P
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>When it starts up, <B
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CLASS="COMMAND"
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>init</B
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> reads the
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<TT
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CLASS="FILENAME"
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>/etc/inittab</TT
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>
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configuration file. While the system is running, it will
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re-read it, if sent the HUP signal (<B
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CLASS="COMMAND"
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>kill -HUP 1</B
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>);
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this feature makes it unnecessary to boot the system to make
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changes to the <B
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CLASS="COMMAND"
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>init</B
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> configuration take
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effect.</P
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><P
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>The <TT
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CLASS="FILENAME"
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>/etc/inittab</TT
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> file is
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a bit complicated. We'll start with the simple case
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of configuring <B
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CLASS="COMMAND"
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>getty</B
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> lines. Lines in
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<TT
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CLASS="FILENAME"
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>/etc/inittab</TT
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> consist of four colon-delimited
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fields:
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<TABLE
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BORDER="1"
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BGCOLOR="#E0E0E0"
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WIDTH="100%"
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><TR
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><TD
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><FONT
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COLOR="#000000"
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><PRE
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CLASS="SCREEN"
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>id:runlevels:action:process</PRE
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></FONT
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></TD
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></TR
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></TABLE
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>
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The fields are described below. In addition,
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<TT
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CLASS="FILENAME"
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>/etc/inittab</TT
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> can contain empty lines, and
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lines that begin with a number sign (`<TT
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CLASS="LITERAL"
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>#</TT
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>');
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these are both ignored.
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<DIV
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CLASS="GLOSSLIST"
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><DL
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><DT
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><B
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>id</B
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></DT
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><DD
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><P
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> This identifies the line in the file. For
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<B
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CLASS="COMMAND"
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>getty</B
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> lines, it specifies the terminal
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it runs on (the characters after <TT
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CLASS="FILENAME"
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>/dev/tty</TT
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>
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in the device file name). For other lines,
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it doesn't matter (except for length restrictions),
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but it should be unique.
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</P
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></DD
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><DT
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><B
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>runlevels</B
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></DT
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><DD
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><P
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> The run levels the line should be considered
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for. The run levels are given as single digits,
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without delimiters. (Run levels are described
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in the next section.)
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</P
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></DD
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><DT
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><B
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>action</B
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></DT
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><DD
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><P
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> What action should be taken by the line, e.g.,
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<TT
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CLASS="LITERAL"
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>respawn</TT
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> to run the command in the
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next field again, when it exits, or <TT
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CLASS="LITERAL"
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>once</TT
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>
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to run it just once.
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</P
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></DD
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><DT
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><B
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>process</B
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></DT
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><DD
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><P
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> The command to run.
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</P
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></DD
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></DL
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></DIV
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>
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To start a <B
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CLASS="COMMAND"
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>getty</B
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> on the first virtual terminal
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(<TT
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CLASS="FILENAME"
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>/dev/tty1</TT
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>), in all the normal multi-user
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run levels (2-5), one would write the following line:
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<TABLE
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BORDER="1"
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BGCOLOR="#E0E0E0"
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WIDTH="100%"
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><TR
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><TD
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><FONT
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COLOR="#000000"
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><PRE
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CLASS="SCREEN"
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>1:2345:respawn:/sbin/getty 9600 tty1</PRE
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></FONT
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></TD
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></TR
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></TABLE
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>
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The first field says that this is the line for
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<TT
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CLASS="FILENAME"
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>/dev/tty1</TT
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>.
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The second field says that it applies to run levels 2, 3, 4,
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and 5. The third field means that the command should be run
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again, after it exits (so that one can log in, log out, and
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then log in again). The last field is the command that runs
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<B
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CLASS="COMMAND"
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>getty</B
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> on the first virtual terminal.</P
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><P
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>Different versions of <B
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CLASS="COMMAND"
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>getty</B
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> are run
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differently. Consult your manual page, and make sure it is
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the correct manual page.</P
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><P
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>If you wanted to add terminals or dial-in modem lines to a
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system, you'd add more lines to <TT
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CLASS="FILENAME"
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>/etc/inittab</TT
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>,
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one for each terminal or dial-in line. For more details, see the
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manual pages <B
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CLASS="COMMAND"
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>init</B
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>, <TT
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CLASS="FILENAME"
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>inittab</TT
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>,
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and <B
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CLASS="COMMAND"
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>getty</B
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>.</P
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><P
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>If a command fails when it starts,
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and <B
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CLASS="COMMAND"
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>init</B
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> is configured to
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<TT
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CLASS="LITERAL"
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>restart</TT
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> it, it will use a lot of
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system resources: <B
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CLASS="COMMAND"
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>init</B
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> starts it,
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it fails, <B
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CLASS="COMMAND"
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>init</B
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> starts it, it fails,
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<B
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CLASS="COMMAND"
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>init</B
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> starts it, it fails, and so on, ad
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infinitum. To prevent this, <B
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CLASS="COMMAND"
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>init</B
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> will keep
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track of how often it restarts a command, and if the frequency
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grows to high, it will delay for five minutes before restarting
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again. </P
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></DIV
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><DIV
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CLASS="NAVFOOTER"
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><HR
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ALIGN="LEFT"
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WIDTH="100%"><TABLE
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SUMMARY="Footer navigation table"
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WIDTH="100%"
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BORDER="0"
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CELLPADDING="0"
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CELLSPACING="0"
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><TR
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><TD
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WIDTH="33%"
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ALIGN="left"
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VALIGN="top"
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><A
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HREF="init-process.html"
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ACCESSKEY="P"
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>Prev</A
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></TD
|
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><TD
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WIDTH="34%"
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ALIGN="center"
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VALIGN="top"
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><A
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HREF="index.html"
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ACCESSKEY="H"
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>Home</A
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></TD
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><TD
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WIDTH="33%"
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ALIGN="right"
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VALIGN="top"
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><A
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HREF="run-levels-intro.html"
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ACCESSKEY="N"
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>Next</A
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></TD
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></TR
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><TR
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><TD
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WIDTH="33%"
|
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ALIGN="left"
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VALIGN="top"
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><B
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CLASS="COMMAND"
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>init</B
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> comes first</TD
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><TD
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WIDTH="34%"
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ALIGN="center"
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VALIGN="top"
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><A
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HREF="init-intro.html"
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ACCESSKEY="U"
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>Up</A
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></TD
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><TD
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WIDTH="33%"
|
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ALIGN="right"
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VALIGN="top"
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>Run levels</TD
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></TR
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></TABLE
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></DIV
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></BODY
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></HTML
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> |