1. Learning Linux – Part 2
CentOS 6.2

2. Topics
• Command-Line Basics
• Permissions
• Using the man Command
• Hard and Soft Links
• Network settings
• Creating RPMs
• Repositories and working with YUM
• Kernel Modes
• Resizing Partitions

3. Command-line Interfaces
Ctrl + Alt + <F2 - F6> (multiple logins simultaneously)

4. Navigating Files and Directories
man <command> manuals lists information about the command
ls list lists all non-hidden contents of a directory
cd <directory> change directory moves into a directory located within
current directory
cat <file> concatenate files print file contents to screen
cp <file1> <file2> copy creates a new file2 with file1 contents
rm <file name> remove removes the file
mv <file1> <new filename> move renames file1
mv <file1> <location> move moves file1 to a new location
cd .. change directory moves up a folder
mkdir <new directory name> make directory makes a new directory
pwd print working directory lists pathname of the current directory
cd ~<username> change directory move into the home directory of user
cd <directory path> change directory moves into the directory
rm -r <directory name> remove recursively removes a directory and its contents

5. Tar Archiving and Gzip Compression
Archiving - grouping multiple files together in a single file to save space
and make it easier to transfer the files around
Compressing - replacing a single file with a smaller/compressed
version to save space
Tar - a type of archiver most common to Linux
Gzip - a type compressor most common to Linux
To extract .tar.gz files:
tar -xvzf <filename>
tar -xvzf example.tar.gz
To create a new .tar.gz file:
tar -cpzf <filename> <foldername>
tar -cpzf newArchive.tar.gz images

6. Users and Groups
Command Definition Purpose
su substitute Similar to logging into your computer
user as administrator
useradd <username> user add adds a new user
passwd <username> password changes or creates new password
groupadd <groupname> group add creates new group
usermod <options> <username> user modify modifies the user
Ex. adding user to group
userdel <username> user delete deletes a user
groupdel <groupname> group delete deletes a group

7. Permissions Format
• A permission has a total of 10 characters.
• There are no empty spaces
ugo
Permission Format
u - user/owner
g - users of the owning
group
o - any other user

8. Permissions Characters
Identifier categories
• - file identifier
• d directory identifier
rwx categories
• r read (able to open/view files as well as view contents of folders)
• w write (able to edit/rename/save files and folders)
• x execute (able to run a program)
• - place holder (does not have the privilege)

9. Permissions Commands
• Changing permissions can be done with the command chmod in the terminal
Command Definition Purpose
ls -lh list lists a long humanly
readable list of all files
chmod <u,g,o> <+,-,=> <r,w,x> change mode changes permissions of
files
• chmod can be used with multiple modifiers
Modifier Purpose
+ adds to current permissions
- takes away from current
permissions
= erases previous permissions and
sets new ones

10. Permissions
• You can set who can access specific files by changing user
and group owner
• The superuser (root) has full access and can change any
permission, even for files that don't belong to the root
account.
Command Definition Purpose
chown <username> <filename> change owner changes the owner of a file
chgrp <groupname> <filename> change group changes the group owner
of a file

11. The man command
• The Linux man pages are the most helpful
tool to the for the test.
• The above is a manual page for the ls
command

12. Strategies and Use
• The manual pages are organized in the order:
– Name, Synopsis, Description, and Options
• The options are organized into subcategories:
– User Commands, System Calls, C Library Functions,
Devices and Special Files, File Formats and
Conventions, Games, Miscellanea, System
Administration.
• If you know what you are looking for and where to look it
saves a lot of time
• Syntax for the command is as follows:
man <command> <options>
man –k <something> | less

13. Strategies and Use
• Once you are in a man page, there are other ways
to help narrow down what you are looking for.
• By typing /<search parameter> and hitting Enter,
you can search for key words within the manual.
Sequentially typing / and hitting Enter bring up the
next occurrences of your search.

14. Strategies and Use
• When searching, pressing the space bar will take
you down one page and help ensure you don’t
miss anything
• To close a manual page, type q or hit ctrl-c which
is the stop current command hot key
• One other method for finding the correct command
is through /sbin where all the executable
commands are stored. Scrolling through the list
with | less can help jog a person’s memory

15. Hard and Soft Links
• Every file has two parts, a data structure and file
name structure.
• The data structure is associated with an inode.
• The file structure is the name and the associated
inode number that references where the data is
stored.
• A hard link refers to more than one file with the
same inode number.
• A soft link is a reference to another file or directory
with a different inode number than the original file.

16. Hard and Soft Links
• ls –lia Shows inode numbers of files
Create hard links
• ln <source-filename> <link-filename>
Create soft Links
• ln –s <source-filename> <link-filename>

17. Network Settings
To display the current network settings, use the command:
ifconfig
This will list all the different interfaces. Choose the one you want and
use the command:
ifconfig <interface> <ip address> netmask <netmask> up
To set the default connection, use the command
route add default gw <default gateway>
To set the DNS, modify the /etc/resolv.conf with the vi or grep text
editor.
It should resemble nameserver <DNS Address>
To configure network with DHCP, run the command dhclient –r which
will release the current client. After run dhclient to obtain a new IP.

18. Creating RPMs
RPM is the package management system used by Red Hat
Enterprise Linux and many other Linux distributions.
Basic Usage:
$ rpm -ivh demofile-1.0.0-i386.rpm
i for install, v for verbose, h for process hash
$ rpm -ql demofile
q for query, l for list files
$ rpm -e demofile
e for erase
Setup:
$ mkdir -p ~/rpmbuild/{BUILD,RPMS,SOURCES,SPECS,SRPMS}
$ mkdir -p ~/rpmbuild/RPMS/{noarch,i386,i686}

19. YUM Repositories
Yellowdog Updater Modified
Package manager for .rpm files that allows the installation of new packages, removal of old packages, and
automatic system updates
yum install <application>
yum install nano
yum update <application>
yum update flash-plugin
yum update (no other parameters)
yum remove <application>
yum remove vim
yum list

20. Kernel Modes
• Within every Linux operating system there are the
six basic runlevels.
• The runlevel is the state of the machine after boot.
• A typical computer boots into runlevel 5. This
usually contains a GUI and networking.

21. Kernel Modes
• These runlevels can be accessed in three main
ways
– With the init command
– Modifying the /etc/inittab file that controls what
the computer boots into
– Changing command sent by the GRUB
Bootloader
**Note when running init command or modifying
innitab file, you need root privileges.**

22. Kernel Modes
• When you start up a computer, press any key to
load the grub menu when the loading screen
appears
• It will then take you to the GRUB menu
• Once in the menu, you can scroll up and down to
chose which version of Linux you would like to
load.

23. Kernel Modes
• You also have the option to open the grub
command line when you press c.
• To modify boot command, press e.
• To change the runlevel the computer boots into,
add a space at the end of the command and type
the runlevel code (1-6) and hit Enter
• Once loaded into one of the runlevels you can
modify the root password with passwd
• To change runlevels after loading into a runlevel,
use init <runlevel id #> (Root only).

24. Kernel Modes
• How is this secure?
• You can establish a GRUB menu password with
the command grub-md5-crypt, but this has its
drawbacks.
– If you forget GRUB password, you may need to
backup your computer and reinstall the
operating system through the BIOS and wipe the
hard drive.

25. Summary
• Command-Line Basics
• Permissions
• Using the man Command
• Hard and Soft Links
• Network settings
• Creating RPMs
• Repositories and working with YUM
• Kernel Modes
• Resizing Partitions

26. Questions?