Ubuntu Practice and Configuration

Ubuntu Practice and Configuration
Post Installation Exercises
APRICOT 2008
Taipei, Taiwan

1. Get used to using sudo
2. Create an inst account
3. Learn how to install software
4. Update /etc/apt/sources.list
5. Install gcc and make
6. Learn how to control services
7. Use the ip tool
8. Create the locate database
9. So, you wanna be root...
10. Install Apache Web Server and PHP
11. Install Gnome 2.x
12. Configure XWindow

1.) Get used to using sudo

Ubuntu and Debian approach system administration a bit differently than other Linux distributions.
Instead of logging in as the “root” user to do system tasks, or becoming root by using the su command
you are encouraged to do your system administration using sudo. By default your user has privileges
to do this. Let's practice this by running some privileged commands from your user account.

First, log in if you have not done so. Once you are logged in you'll see something like this:

user@pcn:~$

We'll represent this prompt with the abbreviation “$”.

Now try to look at the system password file with actual encrypted passwords:

$ less /etc/shadow

The first time you attempt this it will fail. Instead do the following:

$ sudo less /etc/shadow

You will be prompted for a password. This is your user's password. Type it in and you should see the
contents of the protected file /etc/shadow (press “q” to exit the output on the screen).

If you wish to issue a command that requires system privileges, use the sudo command. For instance,

if you are interested in seeing what groups your account belongs to you can type:

$ sudo vigr

You are now in the vi editor (you have a handout to help you with this editor). Type:

/yourUserid

Then press the “n” key for “next” to see each group you belong to. Notice that you are in the “adm”
group. To exit vi type:

:q!

Get used to using “sudo” to do your system administration work. Exercise number 9, will give you a
couple of other options for using system privileged commands as well.

2.) Create an inst account

If you are used to many Linux distributions, then you think of the adduser and the useradd
commands as being equivalent. One is simply a link to the other. In Debian/Ubuntu this is not true.
They are distinct commands with different capabilities. If you are interested in the differences type:

$ man adduser
$ man useradd

As you can see the adduser command is considerably more powerful. This is what we will use to
add a new user and to manipulate user accounts later on.

At this point we would like you to create an account named inst with a password given in class. This
allows your instructors, your fellow students or yourself a way to access your system if necessary. To
do this type:

$ sudo adduser --shell /bin/bash inst

You may be be prompted for your user password to use the sudo command.

You will be prompted for a password. Use what the instructor gives in class. Please be sure to use this
password. Your session will look like this:

user@pcn:~# adduser --shell /bin/bash inst
Adding user ìnst' ...
Adding new group ìnst' (1001) ...
Adding new user ìnst' (1001) with group ìnst' ...
Creating home directory `/home/inst' ...
Copying files from `/etc/skel' ...
Enter new UNIX password: <ENTER pw given in class>
Retype new UNIX password: <ENTER pw given in class>
passwd: password updated successfully

Changing the user information for inst
Enter the new value, or press ENTER for the default cont: ==>
Full Name []: <Press ENTER for default>
Room Number []: <Press ENTER for default>
Work Phone []: <Press ENTER for default>
Home Phone []: <Press ENTER for default>
Other []: <Press ENTER for default>
Is the information correct? [y/N] y <Press ENTER for default>
user@pcn:~#

At this point you are done and the user inst now exists on your machine.

In order to allow the new inst user to use the sudo command it must be a member of the adm group.
To do this you can type:

$ sudo usermod -G adm inst

And, to verify that inst is now a member of the adm group:

$ groups inst

3.) Learn how to install software

This is a large topic. Your instructor should have discussed this with you previously. In general you can
use apt-get to install software, clean up software installs, remove software and update your
repositories. You can use aptitude as a meta-installer to control apt. The dpkg command extracts
and installs individual Debian packages and is called by apt. In addition, synaptic is a graphical
interface to apt that can be used in Gnome or KDE. Finally, apt-cache allows you to view
information about already installed packages.

We are going to concentrate on the apt-get method of software installation. But you should spend
some time reading about and learning about how apt (in general), aptitude, dpkg, apt-cache,
and synaptic work. To do this read the man pages for each:

$ man dpkg
$ man apt
$ man apt-get
$ man aptitude
$ man apt-cache

You don't need to read each man page in detail as this could take a while, but review them enough to
understand the basics of each command and how they differ.

After reading try a few commands:

$ dpkg
$ dpkg –help | more [space for next page, or CTRL-C to exit more screen]

$ apt-get | more
$ sudo apt-get check [what does the “check” option do?]
$ aptitude [Look around at what is installed.]
$ apt-cache | more
$ apt-cache stats
$ apt-cache search nagios2
$ apt-cache showpkg nagios2 | more

4.) Update /etc/apt/sources.list

When using apt, apt-get, aptitude and/or synaptic there is a master file that tells Ubuntu
where to look for software you wish to install. This file is /etc/apt/sources.list. You can update this file
to point to different repositories (third party, local repositories, remove the cdrom reference, etc...). In
our case we are now going to do this. We'll edit this file and we are going to edit out any reference to
the Ubuntu 7.10 cdrom, which is left from the initial install.

To edit the file /etc/apt/sources.list do:

$ sudo vi /etc/apt/sources.list

In this file we want to comment out any references to the Ubuntu cd-rom. You'll see the following lines
at the top of the file:
#
# deb cdrom:[Ubuntu-Server 7.10 _Gutsy Gibbon_ - Release i386 (20071016)]/ gutsy main restricted

deb cdrom:[Ubuntu-Server 7.10 _Gutsy Gibbon_ - Release i386 (20071016)]/ gutsy main restricted

Update this by simply commenting out the one line (see your vi reference sheet for help):
#


Now the apt command (apt-get) won't attempt to read your cd-rom drive each time you install
software.

Change your sources list:

We won't be doing this, but take a closer look at the file /etc/apt/sources.list. You should see multiple
entries along the line of “http://CC.archive.ubuntu.com/” where the “CC” is a country code. If you
installed and said that your location was Taiwan, then the entry would read,
“http://tw.archive.ubuntu.com/”, and so forth.

If you make changes to this file, then you should remember to run:

$ sudo apt-get update

To make sure that all your local repository lists are up to date.
5.) Install libc, gcc, g++ and make

Two items missing from a default Debian/Ubuntu installation are gcc and make plus their associated
bits and pieces. This can be quite disconcerting if you are used to compiling software under other
versions of Linux. Luckily there is an easy way to install all the bits and pieces you need to use gcc
and/or make. Simply do:

$ sudo apt-get install build-essential

and respond with a “Y” when asked if you “...want to continue”. Once the installation process finishes
you should have both gcc and make installed on your machine.

This is an example of installing software using a “meta-package.” If you type in the command:

$ sudo apt-cache showpkg build-essential

You will see a descriptive list of all the various pieces of software that are installed for this package.

6.) Learn how to control services

The first thing to remember is that if you install a new service, say a web server (Apache), then Ubuntu
will automatically configure that service to run when you reboot your machine and it will start the
service immediately!

This is quite different from the world of Red Hat, Fedora, CentOS, etc. In order to configure and
control services the core tool available to you is update-rc.d. This tool, however, may not be the
easiest to use. Still, you should read and understand a bit about how this works by doing:

$ man update-rc.d

There are a couple of additional tools available to you that you can install. These are sysvconfig
and rcconf. Both of these are console-based gui tools. To install them do:

$ sudo apt-get install sysvconfig rcconf

Did you notice that we specified two packages at the same time? This is a nice feature of apt-get.
Try both these commands out. You'll notice that the sysvconfig command is considerably more
powerful. Please don't make any changes to your services at this time.

$ sudo rcconf
$ sudo sysvconfig

Finally, there is a nice Bash script that has been written which emulates the Red Hat chkconfig
script. This is called rc-config. We have placed this script on our “noc” box. Let's download the

script and install it for use on your machine:

$ cd
$ wget http://noc/workshop/scripts/rc-config
$ chmod 755 rc-config
$ sudo mv rc-config /usr/local/bin

At this point the script is installed. You should be able to just run the script by typing:

$ rc-config

Try viewing all scripts and their status for all run-levels:

$ rc-config -l

Now trying viewing the status of just one script:

$ rc-config -ls anacron

You can see how this script works, if you understand enough of bash scripts, by taking a look at it's
code:

$ less /usr/local/bin/rc-config

7.) Use the ip tool

The ip command is a powerful network debugging tool available to you in Ubuntu. You may have
already used this tool in other Linux distributions. But, if not, start by reading:

$ man ip

As you can see this tool is designed to, “show/manipulate routing, devices, policy routing and tunnels.”

For instance, if you are wondering what your default route is (or are) you can simply type:

$ ip route

This is actually short for “ip route show”. Maybe you are wondering out which interface packets
will go to a certain address? A quick way to find out is:

$ ip route get 128.223.32.35

Clearly you can substitute any IP address you wish above. This is useful for boxes that have multiple
network interfaces defined.

Maybe you want to be able to sniff packets coming across an interface on your box. To do this you may
wish to place your interface in promiscuous mode. Often this requires updating a kernel parameter.

With the ip command you can do:

$ sudo ip link set eth0 promisc on

Note the use of “sudo” here as setting an interface requires admin privileges. Now you can snoop the
packets on the eth0 interface by doing:

$ sudo tcpdump -i eth0

Be sure to read the man page for tcpdump if you want further information.

8.) Create the locate database

One of the easiest ways to find files on your system is to use the locate command. For details, as
usual, read the man pages:

$ man locate

We assume you are familiar with this command, but building the locate database is a bit different on
different Linux and Unix versions.

Locate uses a hashed database of f filenames and directory paths. the command searches the database
instead of the file system to find files. While this is much is much more efficient it has two downsides:
1. If you create the locate database as root then users can see files using locate that they
otherwise would not be able to see. This is considered a potential security hole.
2. The locate command is only as precise as the locate database. If the database has not been
recently updated, then newer files will be missed. Many systems use an automated (cron) job to
update the locate database on a daily basis.

To create an initial locate database, or update the current one do:

$ sudo updatedb

Once this process completes (it may take a few minutes) try using the command:

$ locate ssh

Quite a few files go past on the screen. To find any file with “ssh” in it's name or it's path and which
has the string “conf” you can do:

$ locate ssh | grep conf

Read about “grep” using “man grep” for more information. The locate command is very
powerful and useful. For a more exacting command you can consider using “find”. This is harder to
use and works by brute-force. As usual do “man find” for more information.

9.) So, you wanna be root...

As you have noticed Ubuntu prefers that you do your system administration from a general user
account making use of the sudo command.

If you must have a root shell to do something you can do this by typing:

$ sudo bash

This is useful if you have to look for files in directories that would otherwise be unavailable for you to
see. Remember, be careful. As root you can move, rename or delete any file or files you want.

What if you really, really want to log in as root? OK, you can do this as well. First you would do:

$ sudo passwd root

Then you would enter in a root password – definitely picking something secure and safe, right?! Once
you've set a root password, then you can log in as root using that password if you so desire. That's a
controversial thing to do in the world of Ubuntu and Debian Linux.

10.) Install Apache Web Server and PHP

During the week we will be using the Apache Web server (version 2.x) as well as the PHP scripting
language. In order to install these now you can simply do:

$ sudo apt-get install apache2 libapache2-mod-php5

If you are wondering how to find something like “libapache2-mod-php5” here is what your instructor
did:

$ sudo apt-cache search apache | grep php

The output was:
libapache2-mod-suphp - Apache2 module to run php scripts with the owner permissions
php-auth-http - HTTP authentication
php-config - Your configuration's swiss-army knife
php5-apache2-mod-bt - PHP bindings for mod_bt
suphp-common - Common files for mod suphp
libapache2-mod-php5 - server-side, HTML-embedded scripting language (apache 2 module)
php5-cgi - server-side, HTML-embedded scripting language (CGI binary)

Reading the descriptions made it apparent that the version of PHP needed was in the “libapache2-mod-
php5” package.

To test whether or not our Apache install has worked we can use the text-based “lynx” web browser.
This is not installed by default, so first we must do:
$ sudo apt-get install lynx

Once the install completes type:

$ lynx localhost

and you should see the default apache2 directory listed. Press “Q” to quit from lynx. PHP has already
been configured to load and Apache has been reconfigured to execute files with extensions of “.php”,
but because the PHP module was installed after Apache in the command above you must reload/restart
the Apache web server for the new configuration to take affect. There are multiple ways to do this, but
one that is easy to remember is:

$ /etc/init.d/apache2 restart

Go ahead and do this now.

Your instructor will tell you whether to go ahead with the next two exercises.

11.) Install Gnome 2.x

It is actually quite simple to install a graphical desktop on Ubuntu. By default Ubuntu uses the Gnome
desktop. If you wish to use KDE with Ubuntu there is a separate version of the Ubuntu distribution
called Kubuntu that you can find at www.ubuntu.com.

We have configured your workshop lab so that the files for Gnome are on a local machine. The
installation requires over 400MB of files to download and over 1GB of total space. Downloading will
not take long, but unpacking and installing will take some time.

The Gnome desktop comes with the Ubuntu meta-package called “ubuntu-desktop”.

$ sudo apt-get install ubuntu-desktop

This will now take quite some time. Feel free to go to lunch if it is time do to that. If you are around
when this install prompts you to pick a default resolution for your Gnome desktop, then you should
choose: 1280x1024.

12.) Configure XWindow

Ubuntu uses the Xorg XWindow system for the underlying graphics engine that drives the Gnome
Desktop. Once the Gnome desktop is installed along with Xorg you need to configure Xorg to work
with your hardware and the resolution you have chosen. Luckily Xorg has made this quite easy to do.
First do:

$ cd
$ sudo Xorg -configure

This should create the file xorg.conf.new. To finalize configuring your X Server do:

$ sudo cp xorg.conf.new /etc/X11/xorg.conf

Now type:

$ gdm

and your Gnome desktop environment should start. You can log in with your username and password.

Ubuntu Practice and Configuration

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