7/18/2019 Module 03 - Change Runlevels and Shut Down or Reboot System

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Module 03

Change Runlevels

and Shut Down or RebootSystem

7/18/2019 Module 03 - Change Runlevels and Shut Down or Reboot System

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Objectives

Boot the System Boot-time Kernel Parameters

Introduction to Kernel Module Configuration

Change Runlevels and Shut Down or Reboot System Single-ser Mode

!verview of the "etc Directory #ree and the init Process

Setting the Default Runlevel

Determining $our System%s Runlevel

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Boot the System

It is the &ob of a boot loader' such as (I(! )(inu* (oader+

or ,RB ),Rand nified Bootloader+' to launch the (inu*

ernel at boot time

Boot-time Kernel Parameters Set in your boot loader%s configuration file )"etc"lilo.conf or

"boot"grub"menu.lst' and "boot"grub"grub.conf+

/owever' the (inu* ernel also has the ca0ability to acce0t

information at boot time from a ernel command-line interface

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Boot the System

Introduction to Kernel Module Configuration (inu* ernels are modular )modules of code traditionally com0iled into the

ernel )a sound driver+ are loaded as needed

Can be inserted and removed by the su0eruser if necessary )using insmod

and rmmodcommand+

Kernel boot-time messages

1 2s the (inu* ernel boots' it gives detailed status of its 0rogress in theform of console messages3

4 Kernel identification

4 Memory and CP information

4 Information on detected hardware3 mice' diss5

4 6etwor initiali7ation4 Kernel module out0ut for modules that load at boot time

1 #o view messages from the last boot se8uence3 # dmesg | more

Reviewing system logs3

1 found in the system logfiles such as "var"log"messages

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Change Runlevels and Shut Down or Reboot System

Runlevel S0ecifies different ways to use a system by controlling which

services are running

Runlevels are s0ecified by the integers 9 through :

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Change Runlevels and Shut Down or Reboot System

Runlevel 3

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Change Runlevels and Shut Down or Reboot System

Single-ser Mode 3 Runlevel ;' the single-user runlevel' is a bare-bones o0erating

environment intended for system maintenance

Remote logins are disabled' networing is disabled' and most

daemons are not started

!ne common reason you might be forced to use single-user mode

is to correct 0roblems with a corru0t filesystem that the system

cannot handle automatically

#o switch into single-user mode from another runlevel3

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Change Runlevels and Shut Down or Reboot System

!verview of the "etc Directory #ree and the init Process3

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Change Runlevels and Shut Down or Reboot System

!verview of the "etc Directory #ree and the init Process3 "etc"rc3

1 #his file is a scri0t that is used to change between runlevels

"etc"init.d3

1 #his directory contains individual startu0"shutdown scri0ts for

each service on the system1 Exp3 the scri0t/etc/initd/httpd 0erforms some checs before

starting or sto00ing the 20ache web server

1 =alid arguments 3 start! stop! restart! status! reload

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Change Runlevels and Shut Down or Reboot System

!verview of the "etc Directory #ree and the init Process3 #he directories "etc"rc9.d through "etc"rc:.d3

1 #he initiali7ation scri0ts in "etc"init.d are not directly e*ecuted

by the init 0rocess. Instead' each of the directories "etc"rc9.d

through "etc"rc:.d contains symbolic )soft+ lins to the scri0ts in

the "etc"init.d directory.

1

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Change Runlevels and Shut Down or Reboot System

Setting the Default Runlevel3 #o determine the default runlevel at boot time' init reads the

configuration file/etc/inittab

6 is a valid runlevel number' such as >

6ever change the default runlevel to 9 or :

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Change Runlevels and Shut Down or Reboot System

Determining $our System%s Runlevel3 se the runlevelcommand

It dis0lays the previous and current runlevel as integers'

se0arated by a s0ace

If no runlevel change has occurred since the system was booted'

the previous runlevel is dis0layed as the letter "

Exp$ a system that was in runlevel > and is now in runlevel ?' the

out0ut is3

2 system with a default runlevel of ? that has &ust com0leted

booting' the out0ut would be3

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Change Runlevels and Shut Down or Reboot System

Changing runlevels with init and telinit3 #he init or telinit command sends signals to the e*ecuting init

0rocess' instructing it to change to a s0ecified runlevel

#he telinitcommand may be used in 0lace of init.telinit is simplya

lin%to init' and the two may be used interchangeably

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Change Runlevels and Shut Down or Reboot System

System shutdown with shutdown3