This tutorial contains some information about handling a Linux system.

1. Ubuntu

1.1. What is Ubuntu

Ubuntu Linux is a full fledged Linux system trailed for the desktop. Ubuntu builds a unique user interface and offers the users a solid choice of tools.

1.2. Unity as desktop manager

Unity is the default windows manager on Ubuntu. It introduced the launcher on the left side of Ubuntu and the Dash to start programs.

Press the Windows key to start the Dash. Here you can type in commands to open programs and files.

Dash in Action

1.3. Nautilus as file explorer

Ubuntu uses Nautilus as file explorer. Use the Dash or click on the icon in the task manager to start it.

Starting Nautilus

To be able to copy the current path, press Ctrl+L. .

Starting Nautilus

1.4. Adding entries to the launcher

To add new entries to the launcher you can create an .desktop file and drag file on the launcher. For example, the following creates an entry to start Eclipse with different shortcuts for different workspaces.

[Desktop Entry]
Icon=application-x-executable
Name=eclipse
Type=Application
Exec=/home/vogella/Eclipse37/eclipse

X-Ayatana-Desktop-Shortcuts=Docu;vogella;business

[Docu Shortcut Group]
Name=Docu
Exec=/home/vogella/Eclipse37/eclipse -data /home/vogella/workspace/docu
TargetEnvironment=Unity

[vogella Shortcut Group]
Name=vogella
Exec=/home/vogella/Eclipse37/eclipse -data /home/vogella/workspace/vogella
TargetEnvironment=Unity

[business Shortcut Group]
Name=business
Exec=/home/vogella/Eclipse37/eclipse -data /home/vogella/workspace/business
TargetEnvironment=Unity

1.5. Useful shortcuts

The following lists a few useful shortcuts for the Unity window manager.

Table 1. Table Ubuntu general shortcuts

Long press on Super (Windows key)

Opens up help for the most common keyboard shortcuts

Alt+Left Mouse Click

Allows to moves the current window

1.6. Using the console

To open a console open the 'Dash' and type in 'Terminal'. Alternatively you can use the shortcut Ctrl+Alt+T.

This opens a console window which allows you to issue commands.

1.7. Using the vim command line editor

Ubuntu offers several editors which are installed by default. The most common command line editor is vim.

To install vim on your Ubuntu machine use the following command.

sudo apt-get install vim

Start vim from the command line. vim has two modes, one editing mode and other mode in which you can move within the file. To start editing the file, use the "i" key. Once you want to save press the escape button and write ":wq". If you want to exit without saving, use ":q!".

A simple editor with a graphical user interface is gedit.

1.8. Find files

The following demonstrates the usage of the find command.

Table 2. Table Using the find command
Command Description

find dir -name "pattern" 2>/dev/null

Finds all files which recursively apply to the pattern "pattern" starting from the directory "dir". The 2> sends all error messages to the null device.

find . -name '*.java' -newer build.xml -print

Search for all java files newer then the file build.xml

find . -name '*.java' -mtime +7 -print

Search for all java files newer then 7 dates

find . -name '*.java' -mtime +7 -print0

xargs -0 grep 'swt'

The find command can also be combined with the grep command. See Using the grep command.

1.9. Calculate the size of a folder

The following calculates the size (disk usage))of a folder "folder1" in megabyte.

du -sh folder1

1.10. Remove files

Use the command rm pattern to delete files. Be careful with the usage of this command. There is no way to undo deletions.

# Remove all files which ends with .class in the current directory
rm *.class
# find all files which ends with .class recursive in all directories below the current one and delete them
find . -type f -name "*.class" -exec rm -vf {} \;

1.11. Processes

To see all running processes on your system use the ps -aux command.

1.12. Change owner of files and directories

Table 3. Table Using the chown command

Command

Description

chown -R www-data:www-data mydir

Change recursively the owner and the group of the directory "mydir" and its subdirectories.

You can create a soft link to a file or directory using the following command.

# Create a new soft link via
# ln -s target link

# For example
ln -s ~/workspace/e4-dev e4tools

1.14. Zipping files

To zip or unzip files on the command line you can use the following commands.

# Zip all pdf files in the ~/tmp/pdf/ diretory
zip ~/targetdir/myzip.zip ~/tmp/pdf/*.pdf


# Unzip the zip file
unzip ~/targetdir/myzip.zip

1.15. Remove tailing whitespace from files

To remove tailing whitespace from existing files you can use the following command.

find . -type f -name '*' -exec sed --in-place 's/[[:space:]]\+$//' {} \+

<section id="usermanagement"> == User management

1.16. Creating new users

To create a new user via the console use the following commands. This creates the user, set his password and a home directory for the user. The -m parameter is responsible for creating the home directory of the user.

# create user called "newuser" with home directory
sudo useradd -m -s /bin/bash newuser

# assign password to the "newuser" user
sudo passwd newuser

You can create new user groups and add the user to the new group with the following command.

# see existing groups for the user
groups newuser

sudo addgroup gerrit
sudo adduser newuser gerrit

# alternative you can also use the usermod
# command but without -a this removes the user
# from existing groups

# sudo usermod -aG gerrit newuser

1.17. Giving root access

Careful: The following command allows the user to execute sudo commands (root).

# add admin rights to the user "newuser"
sudo adduser newuser admin

# alternative "newuser" can be added to the sudo group
sudo adduser newuser sudo

# afterwards to may want to lock
# the root user
# CAREFUL!!!

sudo passwd -l root

To change the default shell of the user to bash set the last entry of the corresponding user in the /usr/passwd file to /bin/bash. This is demonstrated in the following example.

testuser:x:1001:1001::/home/testuser:/bin/bash

1.18. Manually creating the home directory

In case you need to create the home directory at a later stage you can use the following command which creates the home directory and change this ownership of the directory.

# alternatively to using the -m option
# you could create the
# home directory manually
sudo mkdir /home/newuser
sudo chown newuser /home/newuser
sudo chgrp newuser /home/newuser

1.19. Deleting users

To delete a user use the following command.

# delete the user with the name "userName"
userdel userName

# delete the user and its home directory
userdel -r userName

<section id="environ"> == Environment Variables

Table 4. Table Title

Command

Description

echo $VARIABLE

Prints the content of the environment variable

sudo /etc/init.d/tomcat5 start/stop

Starts / stops the tomcat server

sudo -i

Switches to root

1.20. Add a directory to the path

The PATH environment variable is where the system will look for executable files. To temporary add the /home/vogella/bin directory to the PATH use the following command.

export PATH=$PATH:/home/vogella/bin

If you want to add a directory permanently to the path, you can edit / create the file .bashrc and add the following line to the file. Every new directory in the path must start with :.

PATH=$PATH:path_to_new_directory

Open a new shell to make the changes in the .bashrc file active.

<section id="files"> == Important files

Table 5. Table Title
File Description

/etc/issue

Contains the Ubuntu version you are running

lsb_release -a

Prints out the Ubuntu version you are running

/etc/apt/sources.list

Contains the available sources for software installation

/usr/share/tomcat

Installation directory for tomcat

/var/www/vhosts/domain1

Contains on my v-server the user directory for a specific domain which is hosted on this server

2. Package management

On the command line Ubuntu allows to install / remove and search for packages via the following commands.

Table 6. Table Package management
Command Description

sudo apt-get install paketname

Installs a package

apt-cache search openjdk

Search for all packages which contain openjdk. The found package can get installed via the "apt-get install" command.

apt-cache show eclipse

Write down the meta-data of a package, e.g., the package description and the package maintainer

sudo apt-get remove package

Removes a package but leave the configuration data active

sudo apt-get purge package

Removes a package and orphaned dependencies and its configuration files

sudo apt-get update

Update the local package list

sudo apt-get upgrade

Updates any installed packages for which an update is available. Will not install new packages or remove packages to satisfy dependencies.

sudo apt-get dist-upgrade

Install available updates for the Ubuntu release you already have installed. Also installs new packages or removes existing packages to satisfy dependencies.

dpkg -L packagename

Lists all files and their location in a package

sudo updatedb; locate javac

Updates the installation database and locates the javac command.

To search for the installed packages use the following command.

cat /var/log/dpkg.log | grep "\ install\ "

3. ShellScript

3.1. Writing a shell script

Shell scripts are short programs that are written in a shell programming language and interpreted by a shell process in the console. You can create these programs via a text editor and execute them in a terminal window.

Create for example the following text file.

#!/bin/bash
clear
echo "Hello, world."

You also have to make this file executable via: Create for example the following text file "yourScript".

chmod a+x yourScript

Now you can call the shell script via ./yourScript. It should print "Hello, world" to the console.

3.2. Batch renaming files

The following is an example how to recursively rename all files called "article.xml" to "001_article.xml" from the current home directory.

#!/bin/bash

find . -name "article.xml" -exec rename 's/article/001_article/;' '{}' \;

For to rename all extensions from ".xml" to ".adoc" you can use:

find . -name "*.xml" -exec rename 's/xml/adoc/;' '{}' \;

4. Networkng with Linux

4.1. See all open ports on your machine

You see all listeners on your machine via the following command. Port which listen to 127.0.0.1 cannot get accessed from external.

netstat -anltp | grep "LISTEN"

4.2. SSH access to the server

The ssh command provides secure, encrypted access to a server. Use ssh IP-address or ssh your_hostname to access the server.

You can also assign a shortname for an IP address via the config file in your ~/.ssh director.

For example, to create an alias called foo for the IP address 144.76.74.162 and to use the user called testing switch to your ~/.ssh directory, create the config file if it does not exists and enter the following.

host foo
hostname 144.76.74.161
user testing

To upload your public ssh key which allows you to login automatically into a server use the following command.

ssh-copy-id youruser@yourserver

4.3. Firewall

Ubuntu provides a uncomplicated firewall (ufw). To install it and only allow SSH, FTP, and webtraffic use the following command.

sudo apt-get install ufw
sudo ufw allow 80/tcp
sudo ufw allow 22/tcp
sudo ufw allow 443/tcp
sudo ufw allow 21/tcp
sudo ufw enable

4.4. Network commands

The following commands give you an overview of your network connections.

Table 7. Table
Command Description

lspci -nn

grep -i net

lsusb

iwconfig

ifconfig

Shows the network connections

lsmod

python -m SimpleHTTPServer

4.5. HTTP debugging with curl

curl is a command line tool to issue and receive http (and other) request. For example, if you want to see the HTTP output of a webpage, use the following command.

curl http://www.vogella.com
// Or
curl -G http://www.vogella.com
 If you want to the HTTPrequest header (including the HTTP
status
codes, use the following command. This is for example nice to
see if
your server delivers a 404 return code for your self-defined
error page.
curl -I http://www.vogella.com

You can set HTTP header information with the -h flag. For example, to request a certain MIME type use the -H’Accept:MIME' option.

curl -I http://www.vogella.com -H'Accept:text/plain'

To use curl behind a proxy.

curl -x proxy:8080 -G http://www.vogella.com

If you are using Microsoft Windows, see curl for Windows.

4.6. IRC

For IRC communication you can use the tool xchat. To install it, use "sudo apt-get install xchat".

4.7. FTP

For FTP access you can install filezilla via sudo apt-get install filezilla or map the ftp access to a virtual device.

To map the device select your desktop. Select the file menu and the entry "Connect to server".

ftp menu

5. Installing a FTP server

To install an easy to use and configure ftp server use the following command.

sudo apt-get install vsftpd

6. MySQL

For a description of MySQL and its installation in Ubuntu see MySQL - Tutorial.

7. Apache Tomcat

7.1. Important Files

Table 8. Table
File Description

/usr/share/tomcat5/

Installation directory of Tomcat

psa-webapps

Installation directory for webapps in a vhost environment

/usr/share/tomcat5/conf

Configuration Directory for Tomcat

/etc/default/tomcat5

Contains default settings for tomcat. Most important the used java version (jdk).

/var/log/tomcat5

Log files of tomcat

7.2. Important Commands

Table 9. Table

Command

Description

/etc/init.d/tomcat5 restart

Restart the tomcat web server

8. PDF files

8.1. Command line tool pdftk

The "pdftk" command line tool allows to rework existing pdf files, e.g., extract pages or change the orientation of the pdf file.

You can install it via the following command.

sudo apt-get install pdftk

For example, to extract pages from a pdf document you can use the "cat" option.

# Extract certain pages from a pdf document
# "dont_ask" will override existing files without warning
pdftk Eclipse4book-20120429.pdf cat 25-27 87-91 95 output Eclipse4-Exercise.pdf dont_ask

8.2. Converting .odp file to pdf in batch

If you have LibreOffice installed, you can convert .odp files on the command line to pdf files.

soffice --nologo --invisible --convert-to pdf --outdir ./pdf *.odp

9. Command line tools for adjusting images

ImageMagick allows to convert images in batch see ImageMagick Command line Options.

For example, the following adjusts the DPI size of images to 300.

convert -units PixelsPerInch -density 300 input.png output.png

10. Command line tool for recording the screen

byzanz allows to record a specified area on the screen with different output formats and custom settings.

It can be installed with this command:

sudo apt-get install byzanz

See byzanz command line optionsfor details about the usage.

The following example creates an animated output.gif file of the screen in the area of (x=0, y=0, width=800, height=1024) with the duration of 20 seconds.

byzanz-record --duration=20 --x=0 --y=0 --width=800 --height=1024 output.gif

Besides the gif format also flv, ogg, ogv and byzanz formats are supported. == Spell checking with hunspell

The command line tool hunspell allows you to check the spelling of a document. For example, you can check an XML document written in English called "input.xml" with the command.

# parameter -H defines that the input is an XML file
hunspell -d en_US -H -l input.xml

The following trigger an interactive session for spell checking. With (i) you can add a word to your local hunspell directory, which is located in your home directory under .hunspell_en_US in case you using the US en checker.

You can also check all words in a batch mode with the -l parameter.

# parameter -H defines that the input is an XML file
# all incorrectly spelled words are listed because of the
# -l parameter
hunspell -d en_US -H -l input.xml

11. Connection

11.1. Telnet / ssh client for Windows

To connect to your Linux system via telnet or via ssh from Windows you can use putty.

11.2. Switch to Console mode from Graphical User Interface

In case your Linux system is running under a graphical user interface (KDE, GNOME, …​) and you need access to the console, use the Ctr+Alt+F1 shortcut keys to switch to the first console. To switch back to Desktop mode, use the Ctrl+Alt+F7 shortcut keys.

12. Tips

12.1. Creating a bootable USB disk with unetbootin

The default program for creating a bootable USB disk is Startup Disk Creator. This crashes frequently during the creation of a boot disk. The program unetbootin is much more stable. You can install it via the following command and start it on the command line.

sudo apt-get install unetbootin

To open this type "Menu Manager" in the Dash. Choose "programming" in the left panel. Press "New item" button then. Choose name, command, icon

In the panel click and hold Alt to quick switch/launch apps.

12.2. Chat applications

The mumble application allows online chats.

sudo apt-get install mumble

12.3. Sharing desktop

The Teamviewer application allows to share desktop and online chats. It can be installed from http://www.teamviewer.com/.

12.4. Remote xserver

The x2go server allows to install a X-server on a remote server and access it via a client from a different machine. More information can be found on http://wiki.x2go.org/.

12.5. Eclipse IDE configuration

See Eclipse and Ubuntu for an introduction into the configuration of the Eclipse IDE under Ubuntu.

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