Scribd
Upload
172 views4 pages

1 System Initialization

The document discusses the Linux boot sequence and system initialization process. It begins with the BIOS initializing peripherals and selecting the boot device. Next the boot loader loads and specifies the kernel location. The kernel then initializes devices, mounts the root filesystem, and loads the init process. Init reads the run level configuration and starts scripts to mount filesystems, configure services, and start the graphical display if applicable. System shutdown or reboot is triggered through commands like shutdown, halt, or changing the run level.

Uploaded by

Vignesh Babu
Copyright
© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
Available Formats
Download as PDF, TXT or read online on Scribd
172 views4 pages

1 System Initialization

The document discusses the Linux boot sequence and system initialization process. It begins with the BIOS initializing peripherals and selecting the boot device. Next the boot loader loads and specifies the kernel location. The kernel then initializes devices, mounts the root filesystem, and loads the init process. Init reads the run level configuration and starts scripts to mount filesystems, configure services, and start the graphical display if applicable. System shutdown or reboot is triggered through commands like shutdown, halt, or changing the run level.

Uploaded by

Vignesh Babu
Copyright
© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
Available Formats
Download as PDF, TXT or read online on Scribd
You are on page 1/ 4

RED HAT LINUX SYSTEM ADMINISTRATION

SYSTEM INITIALIZATION

BOOT SEQUENCE OVERVIEW:

BIOS Initialization

Boot Loader

Kernel initialization

init starts and enters desired run level by executing:

/etc/rc.d/rc.sysinit

/etc/rc.d/rc and /etc/rc.d/rc?.d/

/etc/rc.d/rc.local

X Display Manager if appropriate

- BIOS Initialization

peripherals detected, bootdevice selected

- Boot Loader

1st stage- resides in MBR

2nd stage- loaded from boot partition

Minimum specifications for Linux:

Label, kernel location, OS root filesystem and location of the initial ramdisk (initrd)

Minimum specification for other OS:

boot device, label

GRUB and grub.conf

GRUB GRand Unified Bootloader

Supports MD5 password protection

/boot/grub/grub.conf
Changes to grub.conf take effect immediately

If MBR on /dev/hda is corrupted, reinstall the first stage bootloader with:

/sbin/grub-install /dev/hda

- kernel Initialization

Device detection

Device driver initialization

Mounts root filesystem read only

Loads the init process

- init process

/etc/inittab

Run Levels

init defines run levels 0-6, S, emergency

The run level is selected by either

the default in /etc/inittab at boot

passing an argument from the boot loader

using the command init new_runlevel

Show current and previous run levels

/sbin/runlevel

0 - halt

1 - Single user mode

2 - Multiuser, without NFS (The same as 3, if you do not have networking)

3 - Full multiuser mode

4 - unused

5 - X11

6 - reboot

- /etc/rc.d/rc.sysinit
Activate udev and selinux

Sets kernel parameters in /etc/sysctl.conf

Sets the system clock

Enables swap partitions

Sets hostname

Root filesystem check and remount

Activate RAID and LVM devices

Enable disk quotas

Check and mount other filesystems

- /etc/rc.d/rc and /etc/rc.d/rc?.d/

Start and kill scripts of that particular runlevel is going to be happen

Ex: ll /etc/rc.d/rc3.d/

ll /etc/rc.d/rc5.d/

- /etc/rc.d/rc.local

This script will be executed after all the other init scripts

Ex: echo " welcome to \n " >> /etc/issue

- X display

- Controlling services

CONTROL SERVICES MANUALLY:

service: immediately start or stop a standalone service

service network restart

chkconfig: immediately starts and stops xinetd-managed services

chkconfig telnet on

CONTROL DEFAULT SERVICE STARTUP:

system-config-services

ntsysv

ntsysv --level 35
chkconfig

chkconfig --list
chkconfig <service> --list

chkconfig <service> --level 35 on/off

Ex: chkconfig network on

it enables network service on runlevel 2,3,4 & 5.

chkconfig sendmail --level 35 on

it enables sendmail on runlevel 3 and 5

- System Shutdown

shutdown -h now

halt

poweroff

init 0

- System Reboot

shutdown -r now

reboot

reboot -f ==> skipping checking .autofsck

init 6

You might also like