Rendy's Blog » Operating Systems

Linux Tips : Setting Java programming environment in Ubuntu Linux

Rendy — Fri, 01 Jan 2010 08:47:35 +0000

I do a lot of programming in Ubuntu Linux. A couple months ago I started to learn JAVA, previously I have used to program in C/C++ which fortunately Ubuntu is already built in GCC (GNU C Compiler) so everything works out of the box. Unfortunately the case is not the same as JAVA, Ubuntu is not shipped with Java JDK/JRE. So, you must install everything by yourself.

I found out one of my favourite IDE in Windows that support JAVA programming is also available on Linux, it is NetBeans. Netbeans is free Integrated Development Environment (IDE) that supports a lot of languages, including Java, JavaScript, PHP, Python, Ruby, C/C++ and more. NetBeans is written in Java and runs with Java Virtual Machine (JVM) installed. For Java development functionality you must install JDK first, but for other languages you can just install JVM.

Install JDK/JRE Ubuntu Linux

Okay, let’s start with installing JDK and JRE. There are two ways Installing JDK and JRE, the easy way is from Synaptic Package Manager and the hard way is install from .bin file. Installing from Synaptic Package Manager is the best way when you have internet connection or any access to repository (DVD, server, etc). But if your computer don’t have any access to repository server, you can download .bin file from Sun Website from other computer and install it on the computer that you want.

Option 1
First lets start with the easy way, install from Synaptic. Make sure you have the Multiverse repository enabled.

System > Administration > Software Source > Select Multisource > Close

Open your terminal and type the following command to install JDK and JRE

$ sudo apt-get install sun-java6-bin sun-java6-jre sun-java6-jdk

Wait till it download and install, depend on your connection it should take several minutes.
Make sure the correct version is used by using this command

$ sudo update-java-alternatives –s java-6-sun

—

Option 2

For those who want to install the hard way, first download JDK and JRE from Sun. You will get .bin file.

Open your terminal, then go to directory where the download file is, and make sure the file is executable.

cd /directory/where/you/download/file
sudo chmod +x filename

Install the file with this command

sudo ./filename

Make sure the correct version is used by using this command

$ sudo update-java-alternatives –s java-6-sun

Install Netbeans Ubuntu Linux

Option 1
Download Netbeans from here and save it to your computer. Let’s say the file is called “netbeans-6.8-ml-linux.sh”. Run your terminal and change directory to where you download the file.

$ cd /direcory/where/you/download/file

Make sure the file is present by using ls command. Finally execute the following command

$ sudo ./netbeans-6.8-ml-linux

After completing command, you will see installer that will install NetBeans into /opt directory. Finish!.

—

Option 2
Alternatively you can also install using Synaptic Package Manager, just execute the following command.

$sudo apt-get install netbeans

Finish!.

Linux Tips : Automatically find Fastest Repository Server in Ubuntu

Rendy — Tue, 29 Dec 2009 08:23:01 +0000

I used to have problem when updating security update on my Ubuntu 9.10 (Karmic Koala), the connection was extremely slow even when I’m connected to fast network and occasionally the download was dropped without any reason which could lead a disastrous results. So I’ve been researching and I figured it out the problem is with my poor choice of repository server. The Repository Server I’ve had been using is apparently have some problem with their connection. Problem found and this lead to another problem, how do I look for the fastest Repository Server since there’re so many out there.

The answer is to let your system scan for the fastest server available. You will need to launch Software Sources tool, which can be found in

System > Administration > Software Sources

This administrative menu will allow you to change the location of your preferred repository, and change items within the repository you want to subscribe to. You will have the most software available if all boxes are checked.

From ‘Ubuntu Software’ tab select ‘Other’ from ‘Download from:’ drop-down menu and you’ll be given a list of available server sorted with country.

To have your system test and find the faster server you can select the ‘Select Best Server’ option, which will try to connect to each repository server mirror and find the fastest response. After the process done, it will select the fastest server available and you can either change it or run the process again until you’re satisfied.

note: Tested on Ubuntu 8.04 and 9.10. Your mileage may vary. Try to run the process two or three times until you find the good one. Repository mirror speeds can fluctuate based on many factors (e.g Traffic).

Some Example Common DOS commands

Rendy — Sat, 26 Dec 2009 12:20:15 +0000

In previous article I talk about definition of command prompt and real life example of Command Line Interface (e.g Linux). Now, let’s see some common example of DOS commands. If you want to see full list of commands in DOS you can look up Command-line reference A-Z in official Microsoft Website.

Note: Where example files (e.g., file.ext, file1, file2), file extensions (.ext), directories (e.g., diry, diry1, diry2), commands (e.g., command), and drive letters (e.g., a:, b:, c:) are given, substitute the name of your own file, directory, command, or drive letter. Since DOS is not case sensitive, you can type these commands in either upper- or lowercase.

`help`	List commands (only in DOS versions 5 or later).
`help command`	See help for the DOS `command`.
`command /?`	List switches for the DOS `command`.
`path=c:\windows` ; `c:\dos`	Specify in which directories DOS searches for commands or programs.
`prompt $p$g`	Make the DOS prompt display the current directory.
`dir`	List files in the current directory in one column.
`dir /w`	List files in five columns.
`dir /p`	List files one page at a time.
`dir *.ext`	List all files with an `.ext` extension.
`dir z???.ext`	List files with `.ext` extensions that have four letters and start with `z` (where `z` is a character of your choice).
`dir file.ext /s`	Search for the `file.ext` in the current directory and all subdirectories under the current directory; most useful if the current directory is the root (i.e., `C:\` ).
`type file.ext`	View the contents of the text file `file.ext`.
`edit file.ext`	Use the DOS editor to edit the file `file.ext`.
`a:`	Change to the `a:` drive.
`md c:\diry`	Make a new subdirectory named `diry` in the `c:\` directory.
`cd c:\diry`	Change to subdirectory `diry`.
`rd c:\diry`	Remove the existing subdirectory named `diry`.
`del file.ext`	Delete a file named `file.ext`.
`ren file1 file2`	Rename file `file1` to `file2`.
`copy file1 file2`	Copy file `file1` to `file2`.
`verify on`	Turn on verification of copy commands.
`verify off`	Turn off verification of copy commands.
`xcopy diry1 diry2 /s`	Copy all files and subdirectories in directory `diry1` to `diry2`.
`xcopy diry1 diry2 /p`	Ask for confirmation of each file before copying it from `diry1` to `diry2`.
`diskcopy a: b:`	Duplicate a disk using two floppy drives.
`diskcopy a: a:`	Duplicate a disk using the same floppy drive.
`format a:`	Format a floppy disk in drive `a:` .
`format a: /s`	Format a bootable floppy disk (include system files).
`backup c:\diry\*.ext a:`	Back up all files with the extension `.ext` in `c:\diry\` to floppy drive `a:` .
`backup c:\ a: /s`	Back up the entire `c:` drive to floppy drive `a:` .
`restore a:\ c:\diry\*.ext`	Restore backed-up files with the extension `.ext` in drive `a:` to the `c:\diry\` directory.
`restore a: c:\ /s`	Restore backed-up files and subdirectories from drive `a:` to `c:\` .
`ver`	Check the version of DOS.
`time`	Check or correct the system time.
`date`	Check or correct the system date.
`cls`	Clear the screen.
`scandisk`	Scan and check drive `c:` for errors. ScanDisk replaces `chkdsk` (see below) on DOS version 6.0 and above (including Windows 95).
`chkdsk`	Check disk and memory usage of the current disk.
`chkdsk /f`	Fix errors reported by `chkdsk`.
`chkdsk file.ext`	Check a particular file.
`chkdsk a:`	Check a particular drive (in this case, a floppy in the `a:` drive).
`mem`	Check memory usage.

This list was adapted from the August 1991 issue of PC World magazine

What is a command prompt?

Rendy — Sat, 26 Dec 2009 05:01:13 +0000

In previous article I share a list of the common Linux (UNIX Style) command, but what is a command prompt? A command prompt is a non-graphical interface that allows us to interact with our operating system. At the command prompt, you enter commands by typing their names followed by options and arguments. Most modern computers use a graphical user interface (GUI), which allows users to more intuitively access programs and documents. However, some programs and commands are still only available only through a command prompt. To access the command prompt, follow the instructions appropriate to your operating system.

Windows

To access the command prompt in Windows, from the Start menu, select Run… In the “Open:” field, enter cmd (Windows NT, 2000, XP, Vista, 7) or command (Windows 95, 98, and Me).

In next article I’ll talk about some common example of DOS commands.

Mac OS X

Mac OS X built on a version of UNIX called Darwin. To access the UNIX command prompt in MAC OS X, open the Terminal application. It is located by default inside the utilities folder, which in turn is inside the Applications folder. Since, Mac OS X is built on a version of Unix and Linux is Unix-like, so the command on Linux also works on Mac OS X.

You can see the previous article, where I share some Linux Command.

Unix

When you log into a Unix computer, your shell begins to run and provides you with a command prompt. The command prompt’s appearance varies depending on the shell you’re using.

For some common Unix command, you can see my article on Linux command which is Unix-like computer operating System.

Linux Command Line Guide

Rendy — Sun, 20 Dec 2009 23:29:27 +0000

For those who new to world of Linux, and overwhelmed by CLI. I have a Command Line "Cheat Sheet" that might be what you looking for.

Compression
tar cf file.tar files – create a tar named file.tar containing files
tar xf file.tar – extract the files from file.tar
tar cf file.tar.gz files – create a tar with Gzip compression
tar xf file.tar.gz – extract a tar using Gzip
tar cf file.tar.bz2 – create a tar with Bzip2 compression
tar xf file.tar.bz2 – extract a tar using Bzip2
gzip file – compresses file and renames it to file.gz
gzip -d file.gz – decompresses file.gz back to file

Disk Space
ls -lSr show files by size, largest last
df -h show free space on mounted filesystems
df -i show free inodes on mounted filesystems
fdisk -l show disks partitions sizes and types
> file truncate data of file or create an empty file

File Commands
ls – directory listing
ls -a – directory listing with hidden files
ls -al – formatted directory listing with hidden files
cd dir – change directory to dir
cd – change to home
cd - – change back to previous directory
pwd – show current directory
mkdir dir – create directory dir
rm file – delete file
rmdir dir – delete empty directory dir
rm -r dir – recursively delete directory dir (use with caution)
rm -f file – force remove file; no error output if file doesn’t exist
rm -rf dir – recursively force remove directory dir (use with caution)
cp file1 file2 – copy file1 to file2
cp file1 file2 file3 dir – copy file1, file2 and file3 to dir
cp -r dir1 dir2 – recursively copy dir1 to dir2; create dir2 if it doesn’t exist
mv file1 file2 – move file1 to file2 if file2 is an existing directory, moves file1 into directory file2
ln -s file link – create symbolic link link to file
>file – create file (use with caution, doing this on an existing file will overwrite the content)
touch file – create or update file
cat > file – places standard input into file
cat file1 > file2 – overwrites the content of file2 with the content of file1
cat file1 >> file2 – appends the content of file1 to file2
echo "Hello World" > file – overwrites file’s content with Hellow World
echo "Hello World" >> file – appends Hello World to the end of file
less file – output the contents of file
more file – output the contents of file
head file – output the first 10 lines of file
tail file – output the last 10 lines of file
tail -f file – output the contents of file as it grows, starting with the last 10 lines
sed ‘s/foo/bar/g’ file – replaces all occurrences of foo with bar in file
sed -i.backup ‘s/foo/bar/g’ file – replaces all occurrences of foo with bar in file after backing up file as file.backup
rm {m,M}yfile – remove files according to a pattern
Example:
$ ls
$ touch myfile Myfile myfile1 Myfile1
$ ls
myfile Myfile myfile1 Myfile1
$ rm {m,M}yfile
$ ls
myfile1 Myfile1

File Permissions
chmod octal file – change the permissions of file to octal, which can be found separately for user, group, and world by adding:

* 4 – read (r)
* 2 – write (w)
* 1 – execute (x)

Examples:
chmod 777 – rwx for all
chmod 755 – rwx for owner, rx for group and world. For more options, see man chmod

Network
ping host – ping host and output results
whois domain – get whois information for domain
dig domain – get DNS information for domain
dig -x host – reverse lookup host
wget file – download file
wget -c file – continue a stopped download

Package Manipulation
apt-cache show foo – Show info about package foo
apt-cache showsrc – Displays information about a source package
apt-cache showpkg – Displays information about the packages listed on the command line
apt-cache depends foo – Show the depends of package foo
apt-cache rdepends – Shows reverse dependencies for a package
apt-cache search foo – Find packages that include "foo"
apt-cache search –names-only foo – Find packages which have "foo" in the filename
apt-cache pkgnames – Fast listing of every package in the system
apt-cache dump – Lists every package in the cache
apt-cache policy – Lists the repositories in which a package exists
dpkg -L package – List files in the package
dpkg -S foo – Find out which package installed foo
dpkg -c foo – Lists the contents of a binary package
dpkg -f foo – Shows the control file for a binary package
dpkg –get-selections > /path/selectionfile – Get a list of all packages installed
sudo dpkg –set-selections < /path/selectionfile && apt-get dselect-upgrade – Install packages from an exported list
dlocate foo – Determines which installed package owns foo
apt-file search foo – Determines which non-installed package owns foo
sudo aptitude install foo – Install package foo
sudo aptitude remove foo – Uninstall package foo
sudo aptitude purge foo – Uninstall package foo and all of its dependencies
sudo aptitude update – Update the package sources
sudo aptitude safe-upgrade – Update all installed packages to the newest versions
sudo aptitude dist-upgrade – Update the kernel to the newest version
sudo aptitude clean – Remove packages from the package cache

Process Management
ps – display your currently active processes
top – display all running processes
kill pid – kill process id pid
killall proc – kill all processes named proc * file
bg – lists stopped or background jobs; resume a stopped job in the background
fg – brings the most recent job to foreground
fg n – brings job n to the foreground
\ls – ignore alias ls
time command see how long a command takes to finish
which command display the full path of a command
(cd dir && command) go to dir, execute command and return to current dir

Searching
grep pattern files – search for pattern in files
grep -r pattern dir – search recursively for pattern in dir
command | grep pattern – search for pattern in the output of command
updatedb – updates the slocate database; see next item
locate file – find all instances of file; may need to run updatedb first
find $HOME -user root – find files owned by root in $HOME
find /path -depth -type d -empty – find empty directories
find /path -type d -empty -exec rm -rf ‘{}’ \; – find and delete empty directories
find /path -depth -type f -empty – find empty files
find /path -name [name_of_file] – find a file with a specific name
find /path -name "*.[given_extension]" – find a file with a specific extension
find /path -name ‘*.txt’ -perm 644 – find .txt files with specific permissions
find /path -perm -[permission_bits] – find files with some given permissions
find /path -name ‘[given_name].*’ – find files with a given name and any extension
man -t man | ps2pdf – > man.pdf – make a pdf of a man page

Shortcuts
Ctrl+A – move to the start of the line
Ctrl+E - move to the end of the line.
Ctrl+U – delete from the cursor to the beginning of the line.
Ctrl+K – delete from the cursor to the end of the line.
Ctrl+W – delete from the cursor to the start of the word.
Ctrl+Y – pastes text from the clipboard.
Ctrl+L – clear the screen leaving the current line at the top of the screen.
Ctrl+C – halts the current command
Ctrl+Z – stops the current command, resume with fg in the foreground or bg in the background
Ctrl+D – log out of current session, similar to exit
Ctrl+R – reverse search
^abc^xyz – replace first occurrence of abc with xyz in last command and execute it
!! – repeats the last command
sudo !! – repeats the last command with sudo privileges
exit – log out of current session

Software Installation
Install from source:
./configure – execute the configure script
make – compile the source
make install – install needed files
dpkg -i pkg.deb – install a deb package on .deb-based systems
rpm -Uvh pkg.rpm – install an rpm package on .rpm-based systems

SSH
ssh user@host – connect to host as user
ssh -p port user@host – connect to host on port port as user
ssh-copy-id user@host – add your key to host for user to enable a keyed or password-less login

System
date – show the current date and time
cal – show this month’s calendar
uptime – show current uptime
w – display who is online
whoami – who you are logged in as
finger user – display information about user
uname -a – show kernel information
cat /proc/cpuinfo – cpu information
cat /proc/meminfo – memory information
man command – show the manual for command
df – show disk usage
du – show directory space usage
free – show memory and swap usage
whereis app – show possible locations of app
which app – show which app will be run by default
lshw -html > hardware.html – create an overview of hardware
lsb_release -a – show information about the distro
tr : ‘\n’ <<<$PATH – show directories in the PATH, one per line
sed ‘s/:/\n/g’ <<<$PATH – show directories in the PATH, one per line with sed
mount – list currently mounted file systems
mount -o loop cdrom.iso /mnt/dir – mount cdrom image at /mnt/dir
lspci – list all PCI devices
lsusb – list al USB devices
who – list users currently logged in
which command – show the full path of command
time command – see how long command takes to complete

Text Manipulation
sed ‘s/string1/string2/g’ replace string1 with string2
sed ‘s/$.*$1/\12/g’ modify anystring1 to anystring2
sed ‘/ *#/d; /^ *$/d’ remove comments and blank lines
sed ‘s/[ \t]*$//’ remove trailing spaces from lines
echo ‘Test’ | tr ‘[:lower:]‘ ‘[:upper:]‘ case conversion
history | wc -l count lines

Computer Science Course

Rendy — Sat, 28 Nov 2009 14:37:28 +0000

Before we study even deeper it’s always good idea to know what we’re going to study and what we can expect to get by studying it. In this article we’re going to explore all Computer Science Course that you can learn from this website.

Data Storage
In this subject, we consider topics associated with data representation and the storage of data within a computer. The types of data we will consider including text, numeric values, images, audio, and video.
Data Manipulation
In this subject we will learn how a computers manipulates data and communicates with peripheral devices such as printers and keyboards. By learning this subject you can learn the basics of computer architecture and learn how computers are programmed by means of encoded instructions, called machine language instructions.
Operating Systems
In this subject we study operating systems, which are software packages that coordinate a computer’s internal activities as well as oversee its communication with the outside world. It is a computer’s operating system that transforms the computer hardware into a useful tool. The goal learning this subject is to understand what operating systems do and how they do it. Such a background is central to being an enlightened computer user.
Networking and the Internet
In this subject we fill find out the area of computer science known as networking, which encompasses the study of how computers can be linked together to share information and resources. We also going to study construction and operation of networks, applications of networks, and security issues. As a study case we going to use worldwide network knows as the internet.
Algorithms
As we study Computer Science we will learned that the central theme of Computer Science is the study of algorithms. When we reach this subjects it’s time for us to focus on this core topic. Our goal is to explore enough of this foundational material so that we can truly understand and appreciate the science of computing.
Programming Languages
In this subjects we study programming languages. We’re not going to learn all programming languages, that exist in universe. Rather than we going to learn about programming languages. Although I’ll put some programming languages example later on, our goal is to appreciate the commonality as well as the diversity among programming languages and their associated methodologies.
Software Engineering
In this subjects we explore the problems that are encountered during the development of large, complex software systems. The subjects is called Software Engineering because software development is an engineering process. The goal of researchers in software engineering is to find principles that guide the software development process and lead to efficient, reliable software products.
Data Abstractions
This subject will investigate how data arrangements other than the cell-by-cell organization provided by a computer’s main memory can be simulated – a subject known as data structures. The goal is to allow the data’s user to access collections of data as abstract tools rather than force the user to think in terms of the computer’s main memory organization. We will study how to construct such abstract tools to the concept of objects and object-oriented programming.
Database Systems
A database is a systems that converts a large collection of data into an abstract tool, allowing users to search for and extract pertinent items of information in a manner that is convenient to the user. In this chapter we explore this subject as well as take side excursions into the related fields of data mining, which seeks techniques for uncovering hidden patterns in large data collections, and traditional file structures, which provide many of the underlying today’s database and data mining systems.
Computer Graphics
Computer Graphics is the branch of computer science that applies computer technology to produce and manipulate visual representations. We going to explore a filed that is having major impact in the production of motion picture and interactive video games.
Artificial Intelligence
In this subject we explore the branch of computer science known as artificial intelligence. Although this field is relatively young, it has produced some astonishing breakthrough such as expert chess players, computer that appear to learn and reason, and machines that coordinate their activities a common goal. In Artificial Intelligence, everything that seems Science Fiction today’s may be reality for tomorrow’s.
Theory of Computation
This subject we will consider the theoretical foundations of computer science. In a sense, it is the material in this subject that gives computer science the status of a true science. Although somewhat abstract in nature, this body of knowledge has many very practical application. In particular, we will explore its implications regarding the power of programming languages and see how it leads to a public key encryption system that is widely used in communication over the internet.