Linux Intro

1
Linux Intro

• Linux, the do it yourself OS
• Linux, successor to MINIX
• Linux, Unix for the masses (PC users)
• History http//ragib.hypermart.net/linux/

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Linux Organization

• Central core of a Linux system is the kernel
• All CPU communication goes through the kernel
• Network devices are controlled via device drivers
  in the kernel
• The TCP/IP network protocol stack is built into
  the kernel

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Linux Kernel

• Can be modified by the user
• Handles device drivers as needed by hardware
• The kernel can be built for several different
  types of Linux applications

4
Linux Devices

• Devices communicate with the kernel through the
  /dev directory
• Each device has a node number associated with it
  to point to a location in the kernel

crw-rw---- 1 root tty 4, 64 Nov 26
1539 0 crw-rw---- 1 root tty 4,
65 Nov 27 1434 1 brw-------- 1 root root 8,
0 Oct 12 1340 hda0
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Linux File system

• Everything starts at the root (/) directory
• /bin binary executables are here
• /sbin system binary executables are here
• /usr libraries, include files, system files are
  here
• /tmp temporary storage
• /var system logs, spool files, mail, accounting
  here
• /lib library files
• /etc system control files here
• /dev devices
• /proc process storage
• /boot the boot files (kernel etc.) go here

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Linux File system

• Linux always mounts and dismounts all file
  systems.
• Floppies, Zips, Cdroms, and any other random
  access storage is mounted before use and
  dismounted after use.
• Dismounting insures that all writes have
  completed and files are closed before removal of
  the media.

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Linux Swap

• The swap partition is used for virtual memory and
  task swapping.
• Depending on the applications, throughput
  desired, and amount of RAM memory the swap space
  can be from 1 to 3 times the size of RAM.
• Swap space is unformatted disk space

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Linux Basics

• Single boot or Dual boot?
• Partitioning rules
• Format (FAT32, ext2, ext3, swap)
• Common disk partitions
• Install operating system
• Decide what features you need to add such as
  networking, server, development, ganes

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Linux Bootup

• The linux boot program (lilo Linux Loader or
  grub Grand Unified Boot loader) starts the
  linux system.
• After the kernel is loaded and the system can
  talk to its peripherals the initialization
  begins.
• The /etc/inittab file tells the system what to
  start up, the first is usually rc.sysinit.

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Linux Bootup

• rc.sysinit
• Starts logging
• Sets the hostname
• Prepares the network for startup
• Checks the clock
• Sets up the host computer hardware
• Sets up and mounts the filesystem

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Linux bootup

• Depending on the run level that the system is to
  run to, different rc files will be executed.
• Run level 0 is shutdown
• Run level 1 is single user
• Run level 2 is multiuser, no NFS
• Run level 3 is ready to use full multiuser
• Run level 4 is unused at present
• Run level 5 is GUI
• Run level 6 is reboot

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Linux Bootup

• You dont have the root password?

Boot the system in single user mode
Select command line mode from LILIO or GRUB
linux s or linux -single
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Linux bootup

• To keep the startup files organized, they are put
  into a directory /etc/rc.d/init.d
• Links to those programs are placed in the run
  level subdirectories back to init.d so changes
  are only needed in the init.d directory.

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Linux bootup

• To control the sequence of startup processes,
  each start program is start sequentially by the
  numbers before the start script.
• S98http (same as /etc/init.d/http start at
  sequence 98)
• At shutdown the process reverses
• K98http (same as /etc/init.d/http stop at
  sequence 98)
• Init 2, init 3, init 4, and init 5 run the
  Sname scripts
• Init 0, init 1 and init 6 run the Kname scripts

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Linux bootup last step

• Once linux boots and loads the appropriate
  drivers and files it executes login.
• Login provides a prompt for username, then
  prompts for a password.
• The username is stored in /etc/passwd and the
  password is stored in /etc/shadow.
• One the account is authenticated the user is
  given a command prompt ()

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Linux configuration

• Interfaces are configured using the linuxconf
  program (point and click) or command line
  programs.
• The default network interface is called eth0
• The hardware board device drivers is selected via
  the linuxconf program

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GUI configuration

• Linux uses the X window system for its graphical
  user interface
• GUIs are typically installed at system
  installation time.
• If the Linux box is in command line mode then the
  GUI can be installed with the Xconfigurator
  program.
• Linux will probe for the correct video board but
  may need to be told what display is being used.
• The GUI can be set up to start at boot time to
  provide a windows like login screen.

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Linux Networking

• Linux normally will install networking with DHCP
  (Dynamic Host Control Protocol) enabled to
  receive TCP/IP configuration parameters.
• Linux network programs are controlled either by
  starting the program and placing it in the
  background through the /etc/xinit.d dispatcher
  (httpd start) for CPU intensive programs, or by
  calling it as needed via /etc/xinetd.conf to save
  memory and CPU time.

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Linux Network apps

• Shared password file
• NIS (yellow pages) allows sharing of a single
  password file for a group of systems
• NFS (Network File system)
• Allows a group of systems to share a common disk
  farm.

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Linux Network Security

• Linux can filter incoming and/or outgoing ip
  packets to control access to its resources.
• The filter programs are called ipchains or
  iptables depending on the flavor of linux.
• The tables may allow or deny certain ip addresses
  or ports to control access.
• The xinetd program can control which services are
  available to the network

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Knoppix

• Knoppix is the easy way to start into Linux
• Knoppix boots from CD and starts a limited linux
  on any PC.
• Knoppix is free!

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Linux terminal interface

• Linux is ready to take requests from serial
  interfaces as soon as it boots.
• The serial devices use terminal emulators to log
  in to the system (command line mode)
• Modems use the serial ports to access the linux
  box and the system can also be used as a modem
  pool for PPP use.

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Interaction with Linux

• Login
• username user
• Password may not be needed
• Now what?
• ls list files, ls al list with attributes
• man help files
• man k search for key word in man
• ps ef processor status, what is running on the
  system
• df disk free, what disks are there and how much
  is left on them

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More Commands

• grep search files for a string
• paste put two files together
• cut pull a pattern from a file
• tr translate characters
• sort sort a file
• gt, lt, gtgt file redirection
• pipe (flow data between programs)
• grep csh /etc/passwd sort gt file.temp

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Examples

• sort lt file1 gt file2
• cut -d, -f4 file1
• paste file1 file2 gt file3

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Linux Intro
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