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Welcome to Securing Linux Intro to Linux. WK 1 Objectives. Syllabus Intro to Linux ppt Basic commands, Directory structure, & File permissions Remotely log into the Linux network Class Project, Homework. Course Text. Additional Linux Books. Distro types.

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Welcome to Securing Linux Intro to Linux

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Welcome to securing linux intro to linux

Welcome to Securing Linux Intro to Linux

Wk 1 objectives

WK 1 Objectives


  • Intro to Linux ppt

  • Basic commands, Directory structure, & File permissions

  • Remotely log into the Linux network

  • Class Project, Homework

Course text

Course Text

Additional linux books

Additional Linux Books

Distro types

Distro types

  • Installable versions installed to a disk

  • Live versions – bootable cd /dvd

  • VirtualBox – is a virtual engine you can run Linux under VB on windows

  • Unetbootin –

    • utility to make a bootable usb key

  • Embedded versions - DSL embedded

    Download to windows runs on top of windows in a virtual session

Welcome to securing linux intro to linux


  • 1973 Richard Stallman proposed the idea of a free Unix, started the GNU project

  • Started the Free Software Foundation and formulated the General Public License (GPL)

  • Hackers began assisting on projects

  • Became know as the Open Source Movement



  • What does Open Source mean to you?

Linux highlights

Linux Highlights

  • Based on TEXT! Everything treated as a file!

  • ONE Hierarchical file system verse many in Window & DOS

  • Security, file attributes, users groups, privileges, permissions, etc

  • Multi-processing

  • Safe, Stable & Strong!

What is linux

What is Linux

  • Short answer = like UNIX

  • Long answer = a REVOLUTION

Linux is like unix so what is unix

Linux is like UNIX ... So, what is UNIX?

  • developed by Ken Thompson at Bell Labs in 1969

  • was joined Dennis Ritchie (founder of C language)

  • MULTICS had a strong influence on UNIX

  • Ran on PDP-7, PDP-11

  • Both completely rewritten in 1973 using the C programming language (making it portable)

  • due to legal issues, UNIX could not be sold – so AT&T distributed it to educational and research communities

  • once the legal issues were settled, several commercial versions appeared

  • http://plan9.bell-labs.com/who/dmr/

Welcome to securing linux intro to linux


  • a true multi-user and multi-tasking environment

  • designed by programmers for programmers

  • small enough to understand, algorithms based on simplicity, kernel, shell, and library structure is easily expandable yet powerful

  • UNIX was intimately involved with the development of the Internet

  • UNIX erred regarding the desktop PC market

    • Could be as bad as IBM & Microsoft blunder

Unix s strength

Unix’s strength

  • Logical Volume Manager (LVM)

  • Low Cost, Simple, Stable, Scalable, Customizability, Minimalistic and Purpose-built

  • Internet subset of tools

    • TCP/IP

    • FTP

    • Rlogin Slogin

    • Send Mail

    • Telnet

Linux kernel

LINUX kernel

  • In 1991 Linus Torvalds a student rewrote the UNIX kernel and publish it on the Internet (Minix)

  • His instructor said it would never take off

  • Small kernel ran on Intel’s 386 (32-bit cpu)

  • GNU Libraries + Linux kernel = Full functional operating system

  • The rest is history!

Linux kernel poster

Linux kernel Poster

  • http://www.linuxdriver.co.il/kernel_map_poster

Pro s


  • $$$$$$$$ FREE $$$$$$$$$$

  • TCP/IP subset = Internet

  • LVM

  • Low Cost, Simple, Stable, Scalable, Customizability, Minimalistic and Purpose-built

  • Supports many file systems

  • Portable – runs on gas pumps

  • Transferable to routers, sans, PDA’s, Phones, etc

  • Example: Google’s 450,000 RedHat servers

  • Open Source more Secure?

Con s


  • Too Many Variant's (maybe 315)????

  • Welcome to the dark side

  • Concurrence not yet there in driver package.

  • Open Source less Secure?

Welcome to securing linux intro to linux




  • Red Hat most popular

  • SuSE most popular in Europe

  • Debian most popular with hackers

  • Standard $30-$50

  • Professional $60-$100

  • Enterprise $100-$200

  • Linux is FREE! You pay for distribution integration the OS, software & support

Linux kernel1

Linux kernel

  • Numbering conventions

  • Even stable 2.0, 2.2, 2.4, 2.6

  • Developmental 2.1, 2.3, 2.5, 2.7

Welcome to securing linux intro to linux


  • Like DOS

  • [doSomething] [how] [toFiles]

  • [doSomething] [how] [sourceFile] [destinationFile]



  • [doSomething] [how] < [inputFile] > [outputFile]



  • [doSomething] [how] | [doSomething] [how] | [doSomething] [how] > [outputFile]



  • Wildcards : * and ?

  • >> redirect to append file



  • Terminals emulators = xterm, konsole, etc

  • Virtual terminals

  • [alt]-[F1], … [alt]-[F6], [alt]-[F7] is GUI

  • [ctrl]-[alt]-[F1], … [ctrl]-[alt]-[F6] from GUI to Virtual terminal

  • Exiting Linux

  • [main menu] - [logout] from KDE

  • Exit or [ctrl]- D from text mode

Getting help

Getting Help

  • man command

  • info command

  • −−help (command --help)



  • [/] forward slash means from root dir

  • [/] = absolute pathing

  • [.] means current directory

  • [..] means parent directory

  • [./] explicitly means look here!

Gui desktops

GUI desktops

  • CDE : Common Desktop Environment, commercial

  • KDE: K Desktop Environment utilities begin with “k” or “kde”

  • GNOME: GNU Network Object Model Environment, utilities begin with “g” or “gnome”

Distribution installation

Distribution Installation

  • SuSE utilizes YAST: Yet Another Software Tool

  • Red Hat utilizes RPM: Red Hat Package Manager

  • Debian utilizes dpkg: Debian Package Manager

Users and groups

users and groups

  • users are identified in the file /etc/passwd

    • user name and user id (uid)

  • groups are identified in the file /etc/group

    • group name and group id (gid)

  • important linux commands:

    • display uid and gidsid

Users and groups1

users and groups

  • root useruid = 0

  • regular useruid >= 500 ?

  • system user0 < uid < 500

    • typically runs daemons (services)

    • does not login

Users and groups2

users and groups

  • root user / system administrator / superuser

    • limit time as root user

    • it is too easy to do great damage!

      • example:rm -r *

  • becoming root user

    • at login

    • su (switch user) command

Users and groups3

users and groups

  • regular user

    • unique account for each user

    • specify a default home directory

      • example:/home/joecool

    • specify a default shell

      • example:/bin/bash

Users and groups4

users and groups

  • system user

    • typically does not require a home directory

    • typically does not require a default shell

  • a secure system should reflect this

    • /etc/passwd

Users and groups5

users and groups

groups represent collections of users

having common needs

an individual user may belong to several groups


Users and groups6

users and groups

  • as a general rule: if a user requires access to certain files and/or to certain devices, then

    • it is better to add the user to the group that is permitted access than to modify the file access rights

File access rights

file access rights

  • the following command is essential in UNIX

  • ls -l

  • read – write – execute triplesr w x

  • user – group – other triplesu g o

  • chown command

  • chgrp command

  • chmod command

File permissions

file permissions

File access rights1

file access rights

  • octal notation is least ambiguous

    • readr4

    • writew2

    • execute x1

  • example:

    • rwx r-x r--equivalent to7 5 4 octal

File attributes

file attributes

  • file attributes are an extension to file access rights

  • limited to linux native file systems: ext2 and ext3

  • basic commands:

    • to display attributes

      • lsattr

    • to set or modify attributes

      • chattr

File attributes1

file attributes

  • important attributes:

    • immutable+i

      • can not be modified, deleted, renamed, nor linked to

      • ideal for system files

    • append+a

      • only additions at the end of the file are permissible

      • ideal for log files

    • scrub+s

      • all blocks zeroed out when deleted

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