Chapter 3 Study Guide

CNT-2311-Chapter 3

Exploring Linux Filesystems

Objectives

• Comparison of Windows and Linux filesystems
• Navigate the directory structure using relative and absolute pathnames
• Types of files
• View filenames and file types
• Use shell wildcards
• Display contents of files
• Search files for regular expressions using grep
• Use vi to modify text files
• Alternatives to vi
• File Hierarchy
• Comparison of Windows v. Linux filesystems�

 

Navigate the directory structure using relative and absolute pathnames 

start in home dir

 use ~ to reference home directories

present dir = pwd

/home/randy/

change dir = cd

cd /etc - change directory to /etc

relative path name = path to the file in relation to the current working directory

".." references the next higher up dir

tab-completion!

 

Types of files

Text, Binary, Executable

Directory = still just a file

Linked = reference other files, shortcut

Special device files = reference hard disks or ports, contained in /dev

Named pipes = communication between process in memory

Created using mkfifo or mknod One process is a reader other is a writer Sockets = named pipes between remote computers Filenames Filename facts 255 max characters alphanumeric, _ -  .   may or may not have extension to denote type Lots of different extensions 

Links

• http://learn.clemsonlinux.org/wiki/File_extensions 
• http://www.debianhelp.co.uk/fileext.htm 
• http://filext.com/alphalist.php?extstart=%5EL  (not limited to linux) 

Commands to view filenames and file types

pwd - Show current directory

pwd - /home/randy

ls -ltr   - Show listing and give color codes to information

listing including file permissions, ownership and date/time stamp.

Executable files: Green

Normal file : Normal

Directory: Blue

Symbolic link : Cyan

Pipe: Yellow

Socket: Magenta

Block device driver: Bold yellow foreground, with black background

Character device driver: Bold yellow foreground, with black background

Orphaned syminks : Blinking Bold white with red background

Missing links ( - and the files they point to) : Blinking Bold white with red background

Archives or compressed : Red (.tar, .gz, .zip, .rpm

Image files : Magenta (.jpg, gif, bmp, png, tif)

View filenames and file types

•  ls -F = gives file type, special character is listed on the left of the name = Metacharacters=

• @ = linked file

• = exe

• / = subdirectory

• = is a socket

• | = named pipe

Other files do not have special character appended to them - they can be anything not listed above

• ls -l = ls long listing

When listing files/directories a special character on the left indicates what type of file it is

• d = dir
• L = linked
• b & c = special device files
• n = named pipe
• s = socket
• - = other - txt, bin

Display contents of files

• vi - editing a file
• emas - alternative to vi
• cat - concatenation - similar to "type" in DOS/Windows.
• tac - reverse concatenation - types file in reverse
• head - displays the top ten lines of a file
• tail - displays the bottom ten lines of a file
• more - displays file page by page
• less - similar to more but allow line by line manipulation

Key Terms

  The tab completion feature is something your really going to like, it makes life much easier for you, rather than typing every single command you type the first character or two and hit the tab key and it finishes it for you.

• ~ metacharacter = represent user's home dir
• Absolute pathname - full path to a file or starting from /
• Binary data file - contains machine language (1 or 0)
• cat - display file contents
• cd - change directory
• Command mode - vi mode for text editing
• Concatenation - joining of text
• egrep = grep -E
• emacas = ediotr macros editor, think of as word pad
• fgrep = grep -F
• Gedit = GUI text editor
• Head - displays first 10 lines, can specify # of lines
• Insert mode - vi mode only allows text into file, no other options
• less command - display file pg. by pg. cursor navigation
• Linked file - file that represents another file
• ll command = ls -l
• more command = displays file pg. by pg. & line by line
• Named pipe file - temp connection that sends info from 1 cmd or process in memory to another, *can represent a file
• Nano editor - terminal text editor, uses ctrl keys for functions and navigation
• od command - displays file contents in octal format
• Parent dir - one dir level up
• Regular expressions - special metacharacters
• Relative pathname - path to a folder relative to the pwd
• Socket file = named pipe between 2 computers
• Special device file - files to identify hardware
• Strings command - search & display text in a bin file
• Tab-completion - press tab to complete path in the shell
• tac command = cat backwards
• Tail cmd = display last 10 lines
• Text tools = program to create, modify, & search txt files
• Wildcard metacharacters = used to match certain characters 

Key Commands

We have some of the key commands listed alphabetically here but the cat command is much like the tac command where cat is used to display the entire contents of a text file the tac command begins with the last line of a file and ends with the the first line of the file. (Just like the word cat backwards is tac)   The " global regular expression print" or grep command searches files for patterns of characters using regular expressions. The egrep & fgrep are other variants of grep that we will talk about later. The print working directory is a useful command to see where you are in a current directory in the tree. And ls command is another useful used for listing files in a given directory.

• cat 
• cd (change directory)
• egrep
• grep
• file
• grep
• head
• less
• ls
• more
• pwd (print working directory)
• strings
• tac
• tail

Regular Expressions

Search files for regular expressions using grep

• grep allows you to search through a file for text argument.

 

• grep "localhost" /etc/hosts

    return lines that include localhost in the file /etc/hosts

• grep -v "localhost" /etc/hosts

    return lines that DONT include localhost in the file /etc/hosts

• grep -l "LOCALHOST" /etc/hosts

    return lines that include localhost in the file /etc/hosts that is not case-sensitive      

Commands to Display Contents of Binary Files

• strings = searching binary file for text
• od = displays file in octal format
• od -x = displays contents in hex

Searching for Text within Files

Tools: grep, awk, sed, vi, emacs, ex, ed, C++, PERL, tcl

Regular expressions

Wildcard metacharacters are interpreted by the shell

Regular expressions are interpreted by text tool program

Wildcard metacharacters match characters in file & dir names

Regular expressions match charters within file

Wildcard metacharacters typically have different definitions than regular expressions

metacharacters

There are more regular expression metacharacters than wildcard metacharacters

===Emacs===
Not installed by default in Fedora 13.

Can run in a GUI environment.

More GUI than vi.

 Written in C and Emacs Lisp.

 Licensed GNU GPL

 Users can combine commands into macros to automate task.

Summary

• Linux file system is a hierarchy,  series of directories

paths are absolute or relative

• Many types of files - text, scripts, executable, dirs, linked, special device
• ls - view file names and many options to modify view
• Wildcard metacharacters help to select multiple files
• Regular expression metacharacters are used in many ways.
• Text files can be viewed differently with commands such as, head, tail, cat, tac, more and less.
• vi is the most common text editor however GUI options exits  

References

• Anatomy of the Linux File System

http://www.ibm.com/developerworks/linux/library/l-linux-filesystem/

• File extensions

http://learn.clemsonlinux.org/wiki/File_extensions

http://www.debianhelp.co.uk/fileext.htm

• Linux/Unix/BSD Post-Exploitation Command List

https://docs.google.com/document/d/1ObQB6hmVvRPCgPTRZM5NMH034VDM-1N-EWPRz2770K4/edit?hl=en_US

• vi tutorial

http://www.unix-manuals.com/tutorials/vi/vi-in-10-1.html

• VI Cheatsheet

 http://www.atmos.albany.edu/deas/atmclasses/atm350/vi_cheat_sheet.pdf

• Learning the vi and Vim Editors

http://www.amazon.com/Learning-Vim-Editors-Arnold-Robbins/dp/059652983X/ref=sr_1_1?s=books&ie=UTF8&qid=1326846342&sr=1-1 

• Command Guides

http://wiki.ihcnt.net/w/Linux_command_guide

http://wiki.ihcnt.net/w/Linux-command-list 

• Emac Guide

http://sean.wenzel.net/docs/emacs/quick_reference/ 

• 15 Practical examples of ls commands

http://www.thegeekstuff.com/2009/07/linux-ls-command-examples/

• 50 Most Frequently Used UNIX / Linux Commands http://www.thegeekstuff.com/2010/11/50-linux-commands/