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Linux Booting. A Typical PC boot. POST (Power on self test) Boot loader (grub, lilo) Kernel Init RC startup scripts. What a Kernel Does?. Logins, Gettys and shells. A getty is a program that spawns a login program. Gettys are “generally” spawned from init.

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a typical pc boot
A Typical PC boot
  • POST (Power on self test)
  • Boot loader (grub, lilo)
  • Kernel
  • Init
  • RC startup scripts
logins gettys and shells
Logins, Gettys and shells
  • A getty is a program that

spawns a login program.

  • Gettys are “generally”

spawned from init.

  • A shell is the program that the

users interact directly with.

  • A shell provides the user with a

command prompt.

slide5
init
  • When it starts up, init reads the /etc/inittab configuration file. While the system is running, it will
  • re−read it, if sent the HUP signal (kill −1 1 ); this feature makes it unnecessary to boot the system to makechanges to the init configuration take effect.
  • The /etc/inittab file is a bit complicated. We'll start with the simple case of configuring getty lines.
general syntax of inittab
General Syntax of inittab
  • id:runlevels:action:process
  • 1:2345:respawn:/sbin/getty 9600 tty1
  • Id-This identifies the line in the file. For getty lines, it specifies the terminal it runs on (the characters after /dev/tty in the device file name). For other lines, it doesn't matter, but it should be unique.
  • Runlevels-The run levels the line should be considered for. The run levels are given as single digits, without
  • delimiters.
general syntax of inittab con t
General Syntax of inittab Con’t
  • Action- What action should be taken by the line, IE), respawn to run the command in the next field again, when it exits, or once to run it just once.
  • Process- The command to run.
linux run levels
Linux Run Levels
  • 0 Halt the system.
  • 1 Single−user mode (for special administration).
  • 2 Local Multiuser with Networking but without network service.
  • 3 Full Multiuser with Networking
  • 4 Not Used
  • 5 Full Multiuser with Networking and X (GUI)
  • 6 Reboot.
rc startup scripts
RC Startup Scripts
  • In each run−level you will find a series of scripts that are run on boot up. The location of these scripts will vary between Linux distributions Generally the first script that is executed is
  • rc.K or rc.S.
rc startup scripts slackware etc rc d
rc.0@

rc.4*

rc.6*

rc.K*

rc.M*

rc.S*

rc.acpid*

Rc.alsa*

rc.atalk

rc.bind

rc.cups

rc.dnsmasq

rc.font.new*

rc.hotplug*

rc.httpd

rc.inet1*

rc.inet1.conf

rc.inet2*

rc.inetd*

rc.ip_forward

rc.local*

rc.modules*

rc.mysqld

rc.nfsd*

rc.pcmcia*

rc.portmap

RC Startup scripts (Slackware) /etc/rc.d/

rc.samba

rc.saslauthd

rc.sendmail*

rc.serial*

rc.sshd*

rc.syslog*

rc.sysvinit*

rc.udev

rc.wireless*

rc.wireless.conf

rc.yp*

select important scripts
rc.0- Runlevel 0

rc.4- Runlevel 4

rc.6- Runlevel 6

rc.K- Single User

rc.M- Multi-user

rc.S- System

rc.bind- DNS Server

rc.cups-Print Server

rc.inet1-Network Config

rc.inet2-Network Service

rc.nfsd- Network File System

rc.pcmcia-PC support

rc.syslog- System log

Select “Important” Scripts