LPI 1.00 101 05-Boot Initialization Shutdown and Runlevels

8/12/2019 LPI 1.00 101 05-Boot Initialization Shutdown and Runlevels

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Linux Junior Level Administration - LPI 102

5 - 1 2004, SaigonCTT All rights reservedLast updated: 26 December 2003

Boot, InitializationShutdown and Runlevels

Chapter 5


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5 - 2 Last updated: 26 December 2003

Objectives

giving commands to the boot loader.

giving options to the kernel at boot time.

checking the events in the log files.

changing to single user mode. shutdown or rebooting the system.

alert users before switching runlevel.

setting the default runlevel.


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Boot stages

1. BIOS Stage

BIOS checks the system (POST - Power On Self Test)

2. Bootloader Stage

The bootloader loads the second stage into memory

3. Kernel Stage

The Kernel is loaded in to memory

4. Init Stage init load all services and user space tools and mounts all

from /etc/fstab


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Demo pictures

GRUB LILO


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Giving kernel options to the bootloader

The list of options supported by the current kernel can

be found in/usr/src/linux/Documentation/kernel-parameters.txt

The kernel options used are always readable from the

file/proc/cmdline

Example: options given to LILO bootloaders

LILO boot: linux aha152x=0x300,10,7

Means that the Adaptec SCSI adapter is at address 0x300 IRQ 10and SCSI-ID 7


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Giving kernel options to the bootloader

Kernel options that must always be used can be

entered in the bootloader's configuration file.

LILO

append=vga=791 hdc=ide-scsi splash=verbose acpi=off

GRUBkernel (hd0,2)/boot/vmlinuz.2.4.20 root=/dev/hda3

vga=791 splash=verbose


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/etc/modules.conf(or conf.modules)

Kernels can be of 2 types:

Monolithic: All device drivers are compiled into the kernel.

Modular: Some device drivers are compiled as loadablemodules.

Module configuration file: New name: /etc/modules.conf or/etc/modprobe.conf

Old name: /etc/conf.modules

In some other distributions,

find in the /etc/modprobe.d/ directory



Boot Log files

As the kernel boots it saves its log messages in an

internal buffer which is readable with the commanddmesg

most of the system messages including kernel

messages are stored in /var/log/messages

The command

tail -f /var/log/messages allows you to read the last 10 lines of the log file, refreshing it when

having new message(s).



LiLo configuration file

This file is read by the LiLo boot loader.

$cat /etc/lilo.conf

prompt

timeout=50

default=linux

boot=/dev/sda

map=/boot/map

image=/boot/vmlinuz-2.4.20-8

label=linux

initrd=/boot/initrd-2.4.20-8.img

read-only

append="root=LABEL=/"



Grub configuration file

This file is read by the Grub boot loader.

Location: /boot/grub/grub.conf

/etc/grub.conf

/boot/grub/menu.lst

$ cat /etc/grub.conf

default=0

timeout=10

splashimage=(hd0,0)/grub/splash.xpm.gztitle Red Hat Linux (2.4.20-8)

root (hd0,0)

kernel /vmlinuz-2.4.20-8 ro root=LABEL=/

initrd /initrd-2.4.20-8.img



Runlevels

Runlevel Description

0 Shutdown

1 Single user mode

2 Multi-user mode (without Network)

3 Full multi-user mode4 unused

5 Full multi-user and GUI mode (redhat)

6 Reboot

The default runlevel is defined in /etc/inittab

id:5:initdefault

Will start the system in runlevel 5



The /etc/rc#.ddirectory

rc.sysinit The startup script launched by init at boot time.

rc.localA script for local startup customizations, started

automatically after the system is running.

rc A script used to change runlevels.

rc[0-6].dDirectories containing symlinks to scripts in/etc/init.d



Displaying the current runlevel

Find the current and previous system runlevel.

Example

# runlevel

runlevelN3

The command runlevel displays the Previous ('N' if None) and thecurrent

The previous runlevel was None (After Booting) and present: 3

runlevel



Changing the runlevel

Changes the current runlevel.

In some dist. /sbin/telinitis linked to/sbin/init.

Example

# init 6

restart system.# init 1

change to single mode.

telinit



/etc/inittabfile format

Each line starting with '#' is a comment.

Each entry uses one line.

Each entry's syntax is as follows:

id:runlevels:action:process



Shutting down the system properly

Before the system is turned off, it needs:

shut down every current runlevel service properly;

unmount all filesystems

Shutdown

init 0

shutdown -hnow

halt

poweroff

Reboot

init 6

shutdown -rnow



shutdowncommand

bring the systemdown.

Options

shutdown [options] time

-c Cancels a shutdown

-f Will not run fsck on the reboot

-F This WILL run fsck on reboot

-h Halts system after shutdown

-k Sends warning / does not shutdown

-n Shuts down without calling init

-r Reboots, does not halt

-t {Seconds}Delay time after killing process (before init)



Summary

giving commands to the boot loader.

giving options to the kernel at boot time.

checking the events in the log files.

changing to single user mode. shutdown or rebooting the system.

alert users before switching runlevel.

setting the default runlevel.



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LPI 1.00 101 05-Boot Initialization Shutdown and Runlevels

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