Information Systems SecurityInformation Systems SecurityLinux IntroductionSupplemental Notes

Command Line InterfacesCommand Line InterfacesVirtual Terminals

◦ CTL-ALT-F#◦ Consoles 1-6 are command line interfaces◦ Console 7 is the graphical interface◦ Each console is independent of the others

Terminal Window (Konsole)◦ Accessed as a shell window in the graphical

interface.◦ Provides an emulation of a virtual console.

2

Linux Help ResourcesLinux Help Resources man pages

◦ online reference manuals◦ example: man man◦ Uses less pager for navigation (man less)

info pages◦ more sophisticated navigation than man pages

(info info) Release notes

◦ /usr/share/doc/release-notes Howto files (Linux Documentation Project)

◦ /usr/share/doc/howto/en/html or txt Package help files

◦ /usr/share/doc/packages/package-name

3

YaST Management UtilityYaST Management UtilityYet another Setup UtilityWorks with command line or graphical

environmentAllows management of

◦ Software packages◦ User & Group Accounts◦ Printer Configuration◦ View Hardware Configuration◦ X Windows configuration

4

Linux Filesystem StructureLinux Filesystem Structure Hierarchical

◦ Tree-structured directories Paths

◦ Absolute Paths always start from / /home/username/.bashrc ~/.bashrc

◦ Relative Paths always start from current directory ../../tmp/test.txt ./bin/test.sh .bashrc

5

Important DirectoriesImportant Directories/ Root directory --- highest layer of file system tree

/bin/ Important executable files required when no other systems are mounted.

/boot/ Static boot loader files, backed up master boot record, kernel files

/dev/ Device files for system hardware components.

/etc/ System configuration files and shell scripts.

/home/ User (home) directories.

/media/ Mount points for removable media

/opt/ Static files for installed applications.

/root/ The home directory for the system administrator.

/sbin/ System binaries. Important programs for system administration.

/tmp/ Temporary files.

/usr/ Application programs, graphical interface files, libraries, shared documentation

/var/ Variable files that can be modified while the system is running.

/proc/ Process files generated dynamically by the kernel. A virtual file system.6

Useful Commands for Useful Commands for DirectoriesDirectories

Command What it does

ls

ls -a

ls -l

ls -R

Lists files

Lists "all" filesLists files in "long" format

Lists files recursively

cd newdir

cd ..

cd -

Change directory to specified directory

Change to parent directory

Change to last directory

pwd Display absolute path for the present working directory

7

Commands to Create and Commands to Create and View FilesView Files

Command What it does

touch filename Creates a new (empty) file, or updates the timestamp on an existing file.

cat filename Displays the content of the specified (text) file(s) on the screen.

less filename Display the contents of a file one page at a time.

head filenamehead -5 filename

Displays the first 10 lines of a file.

Displays the first (5) lines of a file.

tail filename

tail -15 filename

tail -f filename

Displays the last 10 lines of a file.

Displays the last (15) lines of a file.

Displays continuously updated view of the last lines of the file.

8

Commands to Manage Files and Commands to Manage Files and DirectoriesDirectories

Command What it does

cp source dest

cp -R source dest

Copies a file from source to destination

Recursively copies files

mv source dirmv source dest

Moves files from source to destination directory

Renames a file from source to destination

mkdir newdir Creates a new directory named newdir

rmdir dir Removes an EMPTY directory

rm filesrm -r dir

Removes specified files

Recursively removes the content of directories.

9

Linux File System Wild Linux File System Wild CardsCards

Wild cards can be used to represent one or more characters in a path or filename.◦ ? can be used to represent 1 character◦ * can be used to represent a string of 0 or more

characters.Examples:

◦ ls test?.txt lists files like test0.txt, test1.txt, testA.txt, etc.

◦ ls test*.txt lists files like test.txt, test0.txt, test01.txt, testA.txt,

test3X.Y.txt, etc.

10

Commands to Find FilesCommands to Find Files

Command What it does

find path criteria action Dynamic search for files on the command line, starting from "path" to meet specified "criteria" and perform an "action"

locate Search for files using system database of files. Use updatedb command to update the database.

whereis Returns location of binary files (-b), manual pages (-m), or source code (-s) for specified command.

which Returns the full path of the specified command based on a complete search of the PATH variable.

type Determines whether the specified command is a shell built-in command or an external command.

11

Search File Content using Search File Content using grepgrep

Syntax: grep pattern filename(s) Searches the specified file(s) for the given pattern. Patterns may be specified as:

◦ simple patterns (text)◦ regular expressions (symbolic patterns)◦ extended regular expressions (symbolic patterns (use egrep

instead of grep)◦ Use quotation marks to prevent the shell from interpreting special

characters such as ? or *◦ See man 7 regex for more information about regular expressions.

grep examples...◦ grep "root" /etc/*

12

Commands for Archiving and Commands for Archiving and Compressing FilesCompressing FilesCommand What it does

tar cvzf new.tgz dir Creates a zipped (gzip), archive file for the specified directory

tar xvzf new.tgz Extracts a zipped (gzip), archive file into the current directory using a relative directory structure.

gzip -r dir Recursively compresses (zips) all files in the specified directory and its subdirectories.

gzip -d file Uncompresses (unzips) the specified zipped file.

13

•Archiving combines multiple files into a single file.

•Compressing (zipping) a file reduces its size by removing unneeded characters.

•In Linux/UNIX, archiving and compressing a file are two separate steps.

Command ShellsCommand Shells The command shell program provides the command line

interface in a nongraphical environment.◦ Accepts commands entered by the user on the

command line.◦ Runs the specified command and displays the result on

the screen.◦ Also called the command interpreter.

Linux supports a variety of shells:◦ bash - the Bourne Again SHell, default Linux shell◦ sh - the Bourne SH, the original UNIX shell◦ csh - the c shell◦ ksh - the Korn shell◦ zsh - the z shell

14

Using the Command LineUsing the Command LineStart a shell window (Konsole)Using commands --- previous examples...Pipes and redirection

◦ cat /etc/passwd | less (pipe)◦ cat /etc/passwd > mypasswd.txt (redirect)◦ cat /etc/group >> mypasswd.txt

(append)

15

File Ownerships and File Ownerships and PermissionsPermissions All files have a user owner, a group owner, and a set of

permissions. Three permission types: (r)ead, (w)rite, and e(x)ecute Three access classes: (u)ser owner, (g)roup owner, and (o)ther To view ownerships and permissions: ls -l Modifying permissions: chmod

16

Directory Ownerships and Directory Ownerships and PermissionsPermissions

Directories are also files, and have a user owner, a group owner, and a set of permissions.

Read permissions allow a user to list the contents of a directory. Write permissions allow a user to add or remove files in the directory. Execute permissions allow a user to access a file within the directory. Directory permissions are modified with the chmod command.

17

Permissions for Files and Permissions for Files and DirectoriesDirectories

Permissions Regular File Directory

(r)ead View the file View the directory listing

(w)rite Modify the file Add or remove files in the directory

e(x)ecute Run the file Access the directory

18

File and Directory File and Directory PermissionsPermissionsPermissions control access to and use of files

and directories in UNIX/Linux.Use ls -l to view permissions for files.Use chmod to change the permissions for

files.Syntax:

◦ Symbolic: chmod [ugoa][+-=]rwx file(s)◦ Octal: chmod nnn files(s)

19

chmod Symbolic Notationchmod Symbolic Notation chmod [ugoa] [+ - =] [rwx] file(s)

◦ ugoa --- to whom does the change apply? u = user (owner), g = group, o = others, a = all

◦ + - = --- is the change relative or absolute? + => add the specified permission - => remove the specified permission = => set exactly the specified permissions

◦ rwx --- what permissions are being applied? r = permission to read the file or directory w = permission to write to the file or directory x = permission to execute (run) the file or access the directory.

20

chmod exampleschmod examples[elvis@station elvis]$ ls -l foo

-rw-rw-r-- 1 elvis elvis 42 Jan 16 08:09 foo

What is the effect of the following commands? chmod o-r foo chmod g-w foo chmod ug+x foo chmod o+w foo chmod go-rwx foo chmod a-w foo chmod uo-r foo chmod go=rx foo

21

chmodchmod Octal Notation Octal Notation

We've seen symbolic notation with chmod:$ chmod og-r diary

Symbolic notation allows you to add or subtract permissions relative to the current permissions.

We can also use octal notation with chmod:$ chmod 600 diary

Octal notation allows you to easily set all permissions with one command.

22

Interpreting Octal Interpreting Octal NotationNotation In octal notation, each permission has a

specific value: r = 4 w = 2 x = 1The octal permission value for u, g, o is the

sum of the specific permission values:

7 = 4 + 2 + 1 = rwx (all) permissions6 = 4 + 2 = rw- permissions5 = 4 + 1 = r-x permissions4 = 4 = r-- permissions3 = 2 + 1 = -wx permissions2 = 2 = -w- permissions1 = 1 = --x permissions0 = 0 = --- permisssions

23

Octal Notation ExamplesOctal Notation Examples

What is the meaning of the permission values in the following examples?

$ chmod 755 ./project

$ chmod 644 .plan

$ chmod 600 schedule

$ chmod 777 ./bin

$ chmod 750 ./cent297c

24

Text EditorsText EditorsNeeded for editing Linux configuration files,

which are usually ASCII text files.Graphical text editors

◦ gedit, kedit, kate, etc....◦ Work fine as long as there is a GUI...

Terminal based text editors◦ vi, emacs, pico◦ MUST be used in a command-line environment

such as a virtual console as there is no support for graphical text editors.

25

Overview of Terminal Based Text Overview of Terminal Based Text EditorsEditors vi or vim

◦ Most commonly used by system administrators◦ Moderately complex and powerful tool.◦ Installed by default on ALL UNIX/Linux systems --- so it's

always available emacs

◦ Frequently used by programmers.◦ Very complex to learn and use and very powerful.◦ NOT installed by default and is not always available.

pico◦ Simple, menu-driven text editor◦ Easy to learn and use.◦ Not very powerful.◦ May not always be installed, but usually is.

26

vim introvim intro

vivisual editorcommonly used Unix text editor

vimvi improvedupdated version of vi that’s somewhat easier to usedefault version of vi provided with Linux

27

vim basicsvim basics

vim filenamecreates and new file and opens it for editing

vi modescommand mode --- used for entering commands, saving files, and quitting viinsert mode --- used for entering text

The following file includes a summary of vi commands 01_vi.pdf

28

Shell ScriptsShell Scripts

A shell script in Unix is essentially the same thing as a batch file in DOS

A file that contains a sequence of commands that the Unix operating system can interpret and run

To create a Unix scriptCreate the script file using vi or vimSave the fileSet the permissions of the file to make it executable

29

Example of a shell scriptExample of a shell script

prompt% vim myscript.shi (change to insert mode)#! /bin/bash# display the default shellecho $SHELL# display the terminal typeecho $TERMESC (exit insert mode/return to command mode):wq (save file and exit)

30

Setting permissions Setting permissions prompt% ls -l myscript

(displays permissions)

prompt% chmod u+x myscript

uses chmod to make the file myscript executable by adding execute (x) permission to the user (u) permissions.

31

Running the scriptRunning the script

prompt% ./myscript

Note: the filename myscript is preceded by the symbols ./ to indicate that the file is located in the current directory.

In Unix/Linux, the current directory is frequently not in the default search path, so entering myscript without ./ would result in an error message that the command was not found.

32

Sending output to a fileSending output to a fileprompt% ./myscript > myscript.out

As in DOS, the symbol > can be used to redirect the output of a command to a file.

The symbols >> can be used to append the output of a command to an existing (or new) file.

33

If . (or any other path) is not If . (or any other path) is not in your path:in your path:

For bash shell: ◦Edit the .bashrc file: vi ~/.bashrc◦Add the line: export

PATH=$PATH:/addedpath◦set (instead of export) works too◦Source the file: source ~/.bashrc

For csh or tcsh:◦Edit .cshrc file or .tcshrc◦Add line: set PATH = ($PATH addedpath) ◦Source the file

34

How will you know if it’s not How will you know if it’s not in your path?in your path?You won’t be able to run the

command

Use “which” command to find out where the command is◦which ifconfig◦If it is not found, you got to find it and

add it’s path to your PATH variableRun: $PATH to find out what your

path is

35

Networking commands Networking commands and filesand files

http://www.reallylinux.com/docs/admin.shtml Basic commands for sys admins (everything, not only networking)

http://www.yolinux.com/TUTORIALS/LinuxTutorialNetworking.html#CONFIGFILES

http://www.yolinux.com/TUTORIALS/LinuxTutorialNetworking.html Comprehensive sys admin tutorial

36