Thursday, November 22, 2012

Best free Android apps for your phone or tablet


Best free Android 

apps for your phone or tablet



1. Seesmic

There are many Twitter apps on Android - and Twitter itself shook up the scene with the launch of its own-brand app - but we're sticking withSeesmic. Offering support for multiple accounts, a home page widget showing latest tweets and an incredibly slick and professional design, it's one of the finest examples of app development out there today.
Seesmic

2. Facebook for Android

Facebook for Android is lacking in features compared to Facebook itself, but a recent update added Inbox support to the Android app, finally allowing its users to communicate in almost real time. The app's fast and stable, with a simplicity that reminds you of the old days when using Facebook used to be bearable.
Facebook for android

3. National Rail Enquiries

After the original free, third-party National Rail apps went paid-for, National Rail has finally brought out its own free app. National Rail Enquiriesenables you to check live train times, plan your journeys, and get notifications of delays. On first use, the app prompts you to enter a home and work train station, and then you can use the 'Get me home' button to see the next available trains.
National Rail Android app

4. UK Jobs

Hey, times are hard and you've got to pay for your oppressive monthly mobile phone contract somehow. Offering a fully searchable database of current UK job vacancies, UK Jobs, which pulls in its data from independent employment site 1job.co.uk is, a slightly cumbersome but useful and non-governmental tool.
uk-jobs

5. Hotmail

Microsoft has teamed up with developer SEVEN to offer an official Hotmail app for Android, which gives users a simple, clean interface, push notification support and even lets you manage multiple Hotmail accounts from within the app. If your email needs haven't yet been assimilated by Google, it's a useful option.
Hotmail

6. Google Sky Map

A stunning app that renders Patrick Moore obsolete, by using your phone's orientation tools to give you an accurate representation of the stars and planets on your screen. Point your phone at the sky, then learn what constellations are visible and if that's a UFO or just Venus. Google Sky Map even works indoors, if you're not keen on getting cold.
Google sky map

7. Layar

The stunning augmented reality app Layar has recently gone commercial, adding an online shop that allows users to buy AR content such as travel guides, local house price apps and much more. But you're still able to use the numerous free Layers to pop data up over real-world locations, delivering a satisfying futuristic experience.
Layar

8. Foursquare

The social media darling Foursquare is represented in fine form on Android, with the Google app offering easy one-click check-ins, integrated Google Maps for a seamless Google-branded experience and home page shortcut options to all your favourite places.
Foursquare

9. WordPress for Android

WordPress for Android started out as independent creation wpToGo, before WordPress decided it liked it so much it bought it up - hiring the maker to develop it in-house. It's very feature-packed, with the latest version offering full integration with other apps, letting you spin content and send it directly to the app for easy updating. It could do with more image insertion tools, though.
WordPress for android

10. Google Goggles

A bit of a novelty, in that Google Goggles lets you take photos and have Google analyse them and come back with a search results page for what it thinks you're looking at. However, the app's main use is as a QR code reader, which lets you scan barcodes for quick access to apps and whatever data people choose to embed in the odd little data squares.
Google goggles

11. Winamp

Yes, the same Winamp from a decade ago. It's had an Android app for some time, with recent updates adding support for iTunes, Mac syncing, plenty of music streaming options, new release lists and Shoutcast integration for radio support. It's a fine, free media player.
Winamp

12. Samsung ChatOn

There are plenty of messaging tools on Android, but Samsung's beats many of them by offering multi-platform support - with clients even available for older Samsung non-smart feature phones. It could be the ideal way to keep in touch with an out of touch relative. More "with it" users will be able to use its drawing, image sharing and social networking features.
Samsung

13. Skyfire 3.0

The USP of the Skyfire browser is that it supports Flash content, popping up a little window when it detects an embedded YouTube video or something similar. The actual Flash business is handled by Skyfire's server, which does all the computery stuff, then sends the file to your handset. A bit clunky on slower Android phones, but it works like a dream on models with faster processors.Despite the arrival of Flash with Android 2.2, this is still relevant for those on phones and Android versions not able to support Adobe's Flash Player.

14. BBC News

While the BBC's Android iPlayer app is a bit on the disappointing side, the corporation's BBC News app is much more refined. There's a stylish grid-based front page, plus you're able to swipe from left to right to switch between stories in your chosen specialist category. A recent update also added a couple of Home screen widgets, too, plus the ability to submit your own news tips, as if the BBC was a small blog clamouring for content.
BBC news

15. RAC Traffic

An official production of the motoring organisation, RAC Traffic is dead simple - it guesstimates your location via the mobile signal, then pops up the current traffic alerts for your area. It's much better than having to listen to the radio for the odd update about arterial blockages.
RAC traffic

16. Swype

The odd line-drawing alternate keyboard Swype is a love-it or hate-it kind of thing, with the significant amount of re-learning required to make the most of it quite offputting to some users. Once you're familiar with the idea, though, it's genius - with advanced prediction options further speeding your line-typing. Swype is not available through the Android Market - the only way to install is is via a direct download from the maker.

Swype

17. Evernote

After the Android version of Dropbox, the next best solution for keeping all your 'business' in one place is Evernote - which lets you stash and sync all your text notes, voice memos and files on your phone and access them through a desktop computer.
Evernote

18. Flickr

As well as supporting Flickr uploading, this app also lets you capture photos from within the app and comes complete with a set of filters, so you can hipsterise your life with ease. It supports sharing with Twitter and Facebook as well, so your other, non-photo-nerd friends can enjoy the results of today's snapping session.
Flickr

19. Last.fm

The subscription-based thrills of Last.fm open up a world of music streaming on your mobile. You have to 'buy in' to the odd Last.fm way of organising things and suggesting new music, but if you're easily led and not restricted by bandwidth it's a superb tool.
tune in radio

20. Google Maps Navigation

An absolute must-get. As long as you have Android 1.6 or above, the latest update to Google Maps introduces turn-by-turn voice navigation, simultaneously devastating the satnav industry while boosting the in-car dashboard dock/charger accessory scene. Route calculations are done at the outset of your trip, minimising data transfer en route and keeping you on target even when the GPS signal drops. It's amazing, it works, and it's free.
Google maps navigation

21. Catch Notes

A simple note-taking tool, Catch Notes lets you sync those disjointed, late night thoughts you have together into one huge, incoherent database. If you have a Snaptic account you're able to sync the Android app with that too - or you can simply log in with your Google details for instant mobile jotting. Once written, notes may also be pinned to the home screen, creating a little post-it note-style reminder icon.
3banana

22. gvSIG Mini Maps

gvSIG Mini Maps is an incredibly comprehensive mapping tool which combines major online maps including Google, Bing, Open Street Map and more, which will win UK fans for one huge reason alone - it supports the official and recently open-sourced Ordnance Survey data. This means you're never more than a post code search away from seeing where you are in OS-level detail, which offers much more in the way of accurate local data than other map tools provide.
gvsig

23. Astrid Task / Todo list

Astrid describes itself as an "open source" task list, which includes syncing support with rememberthemilk.com for the ultimate in minutiae management. You set a list of tasks and are then able to order them according to their importance - also setting off a timer to see precisely how long you've wasted on Twitter instead of doing the job in hand. It's basically the world's most complex and in-depth personal to do list, which, if used correctly, will consume more time than the tasks themselves. Ideal for expert-level procrastinators.
astrid

24. Shareprice

Shareprice uses your login from financial site www.iii.co.uk to offer live share price updates on your Android phone. Watch your nest-egg lose 50 per cent in value every three weeks during the latest trans-global financial crisis, live! It's ideal for users with share values so low they have to be checked in private, to ensure their partner doesn't see exactly how much money has disappeared into some notional financial black hole.
shareprice

25. Skifta

Skifta is the first software tool to be granted DLNA certification, meaning it turns your Android phone into an official DLNA device. This in turn means streaming all of your household media to your phone, and beaming your phone videos to your TV. Seems a little buggy at the moment, but there are plenty of updates arriving all the time. Requires Android 2.2 or higher.
skifta

26. Dropbox

The Android version of the insanely popular stuff-syncing app has arrived, and while Dropbox is a little lacking in the sort of fancy auto-syncing options many were hoping for, it still works as expected. Files have to be specifically downloaded to your phone to be edited or shared, which is not quite the automated dream offered by the desktop tools, but it's still Dropbox on Android. Six months ago that was a distant, crazy fantasy.
dropbox

27. London Tube Status

Reduce the misery of being told you've just missed a train and it's a 14-minute wait until the next one with London Tube Status, which combines travel status updates and live departure times. It also includes a home screen widget that shows your favourite (or at least your most used) platform departures, making it easy to check how much you've just missed the next one by while tearing down the escalators.
London tube status

28. Amazon UK

Amazon recently launched an official Android app, replacing its reliance on a mobile web store. The app's very simple and fast to use, and even includes full shopping cart features with Amazon's one-click system once you've signed in with your usual account details.
amazon-uk

29. Meebo IM

If you like to pass the time exchanging smiley faces and abbreviations with your friends through instant messaging apps, you ought to get a copy ofMeebo IM. It's an instant messaging aggregator, incorporating AIM, MSN, Yahoo, MySpace, Facebook, good old ICQ and more, serving everything up in one convenient interface. Typing in all your logins and passwords for everything is the only, very temporary, inconvenience.
Meebo im

30. Beelicious

If you're into the slightly last-generation social networking site Delicious, you ought to get yourself organised with one of the many third-party Android apps out there that support the bookmarking tool. Such as Beelicious, which, once you've got through the slightly cumbersome initial set-up process, lets you simply send website links to your Delicious account via the Android browser's 'Share Page' sub menu.
Beelicious

31. TweetDeck

A star on the Twitter app scene, TweetDeck for Android is one amazing little tool. As well as presenting your timeline, DMs and replies in separate side-by-side panels that you swipe the screen to flip between, it can also pull in Facebook status updates. And mix it all in together. And it does Foursquare. And Buzz.
tweetdeck

32. iPlayer

The BBC's iPlayer app is a right weird old mixed bag. On the one hand, support for streaming radio and live TV channels (Wi-Fi only) elevates this over the mobile website, but there's no 3G streaming, not even of radio feeds. And you can't download shows, unlike in the sadly departed Beebplayer. And the radio requires the screen to be on at all times. Strange app, this.
iplayer

33. Google Reader

Google has brought its RSS feed tool into the app era, launching itsGoogle Reader for Android. It's got some great functionality built in, with support for multiple Google accounts and plenty of thread customisation options. You're also able to use the volume rocker to page up and down between messages, which is handy for extra-lazy news assimilation.
Google reader

34. BT FON

BT's incredibly clever FON network is often a lifesaver, letting you legally borrow Wi-Fi for free in many public places. And while standing outside strangers' houses. The BT FON Android app lets you automate the sign-in process, so you can walk around towns and housing estates safe in the knowledge that your phone's always seeking out available Wi-Fi. You need a BT FON username, though, so sort that out before you venture out into the scary internet-free world.
BT fon

35. Amazon Kindle

Amazon's Kindle app is a great e-reader, which is seamlessly linked with your Amazon account. Support for magazines and newspapers is limited at the moment, with only a handful of niche publications in Android-friendly format. But for books it's great, with plenty of screen and text display options to get it looking a way that hurts your eyes the least. Another exciting new way to collect classic novels you'll probably never get around to reading because there's the internet now.
Amazon kindle

36. ES File Explorer

We're officially out-of-love with previous favourite file explorer ASTRO, thanks to it now coming plastered with ads. ES File Explorer is prettier, ad-free, and comes with a much more user-friendly and functional interface. And yes, Android users have favourite file explorers.
ES file explorer

37. Androidify

Let your hair down by creating a realistic interpretation of what you hair looks like with Androidify. It's an avatar creator that uses the Android mascot as its base, letting you swap trousers and hats with the swipe of a finger. Results are then sharable via Twitter and the usual social tools. There aren't enough types of beard, though. Please release a Beard Expansion Pack.
Androidify

38. Kongregate Arcade

Thanks to Android's Flash Player powers, casual gaming portalKongregate is able to bring a huge number of its internet games to Android. They run in the browser so resolutions can be a bit all over the place, but with over 300 games to choose from there's bound to be something there for you.
Kongregate

39. Blogger

The Google-owned Blogger platform now has a presence in the current decade, thanks to the official Blogger app. It's remarkably simple, supports image uploads and geo-tagging and imports the settings of all blogs associated with your Gmail account. There's no fancy editing the positions of your photos, which just get chucked in at the bottom, but it works.
Blogger

40. RD Mute

RD Mute serves one purpose – to turn off all phone sounds when the Android accelerometer tells it you've picked it up and turned it over. It's a 'silent mode' shortcut for when you can't even be bothered to press a button. Put your phone on its front to shut it up – and add any very important numbers to the app's exceptions list, so people you don't mind talking to can get through.
RD mute

Thursday, November 8, 2012

503 Service Unavailable How To Fix a 503 Service Unavailable Error


  • "503 Service Unavailable"
  • "503 Service Temporarily Unavailable"
  • "Http/1.1 Service Unavailable"
  • "HTTP Server Error 503"
  • "Service Unavailable - DNS Failure"
  • "503 Error"
  • "HTTP 503"
  • "HTTP Error 503"
  • "Error 503 Service Unavailable"
503 Service Unavailable errors can appear in any browser in any operating system.
The 503 Service Unavailable error displays inside the browser window, just as web pages do.

Cause of 503 Service Unavailable Errors

The 503 Service Unavailable error is an HTTP status code that means the web site's server is simply not available right now. Most of the time this is because the server is too busy or because there's maintenance being performed on it.

How To Fix the 503 Service Unavailable Error

The 503 Service Unavailable error is a server-side error, meaning the problem is usually with the web site's server. It's possible that your computer is having some kind of problem that's causing the 503 error but it's not likely.
Regardless, there are a few things you can try:
  1. Retry the URL from the address bar again by clicking the reload/refresh button or pressing F5.

    Even though the 503 Service Unavailable error means that there's an error on another computer, the issue is probably only temporary. Sometimes just trying the page again will work.

    Imporant: If the 503 Service Unavailable error message appears while paying for an online purchase, be aware that multiple attempts to checkout may end up creating multiple orders - and multiple charges! Most payment systems, and some credit card companies, have protections from this kind of thing but it's still something to be aware of.
  2. Come back later. The 503 Service Unavailable error is a common error message on very popular websites when a huge increase in traffic by visitors (that's you!) is overwhelming the servers.

    As more and more visitors leave the website, the chances of a successful page load for you increases.
  3. Restart your router and your computer, especially if you're seeing the "Service Unavailable - DNS Failure" error.

    While the 503 error is still most likely the fault of the web site you're visiting, it's possible that there's an issue with your computer's or router's DNS server configurations and a simple restart of both might fix the problem.
  4. Contact the webmaster. There's a very good chance that the website administrators are already working on fixing the 503 error but you can always try to contact the website directly if think that might not be the case.

    The best way to find a website's contact information is usually through a WHOIS search, using the domain name (e.g. facebook.com) as your search term. If that doesn't get you an email address, the webmaster of most websites can be reached at webmaster@website.com, replacing website.com with the actual website name.

Errors Like 503 Service Unavailable

Tuesday, November 6, 2012

How to Compile a C/C++ Program on Ubuntu Linux

My step by step instructions.

1. Install the 'build-essential' package.


$ sudo apt-get install build-essential

2. Write your first C program. 
gedit myhello.c
paste this code into it, and save

#include <stdio.h>

main()
{
printf("Nothing Is Impossible!\n");
}


3. Compile your first C program

$ gcc myhello.c -o myhello


4. Run your first C program

$ ./myhello 
Nothing Is Impossible!


5. Write your first C++ program


gedit myhello.cpp


paste this code into it, and save


#include <iostream>
using namespace std;

int main()
{
cout << "Hello Ubuntu Lover in C++" << endl;
return 0;
}

6. Compile your first C++ program


g++ myhello.cpp -o myhellocpp

7. Run your first C++ program


$ ./myhellocpp 


Hello Ubuntu Lover in C++




SAGAR VASULE!

49 most frequently used commands in Linux / UNIX.


This article provides practical examples for 50 most frequently used commands in Linux / UNIX.
1. tar command examples
Create a new tar archive.
$ tar cvf archive_name.tar dirname/
Extract from an existing tar archive.
$ tar xvf archive_name.tar
View an existing tar archive.
$ tar tvf archive_name.tar
2. grep command examples
Search for a given string in a file (case in-sensitive search).
$ grep -i "the" demo_file
Print the matched line, along with the 3 lines after it.
$ grep -A 3 -i "example" demo_text
Search for a given string in all files recursively
$ grep -r "ramesh" *
3. find command examples
Find files using file-name ( case in-sensitve find)
# find -iname "MyCProgram.c"
Execute commands on files found by the find command
$ find -iname "MyCProgram.c" -exec md5sum {} \;
Find all empty files in home directory
# find ~ -empty
4. ssh command examples
Login to remote host
ssh -l jsmith remotehost.example.com
Debug ssh client
ssh -v -l jsmith remotehost.example.com
Display ssh client version
$ ssh -V
OpenSSH_3.9p1, OpenSSL 0.9.7a Feb 19 2003

5. sed command examples

When you copy a DOS file to Unix, you could find \r\n in the end of each line. This example converts the DOS file format to Unix file format using sed command.
$sed 's/.$//' filename
Print file content in reverse order
$ sed -n '1!G;h;$p' thegeekstuff.txt
Add line number for all non-empty-lines in a file
$ sed '/./=' thegeekstuff.txt | sed 'N; s/\n/ /'

6. awk command examples

Remove duplicate lines using awk
$ awk '!($0 in array) { array[$0]; print }' temp
Print all lines from /etc/passwd that has the same uid and gid
$awk -F ':' '$3==$4' passwd.txt
Print only specific field from a file.
$ awk '{print $2,$5;}' employee.txt

7. vim command examples

Go to the 143rd line of file
$ vim +143 filename.txt
Go to the first match of the specified
$ vim +/search-term filename.txt
Open the file in read only mode.
$ vim -R /etc/passwd

8. diff command examples

Ignore white space while comparing.
# diff -w name_list.txt name_list_new.txt

2c2,3
< John Doe --- > John M Doe
> Jason Bourne

9. sort command examples

Sort a file in ascending order
$ sort names.txt
Sort a file in descending order
$ sort -r names.txt
Sort passwd file by 3rd field.
$ sort -t: -k 3n /etc/passwd | more

10. export command examples

To view oracle related environment variables.
$ export | grep ORACLE
declare -x ORACLE_BASE="/u01/app/oracle"
declare -x ORACLE_HOME="/u01/app/oracle/product/10.2.0"
declare -x ORACLE_SID="med"
declare -x ORACLE_TERM="xterm"
To export an environment variable:
$ export ORACLE_HOME=/u01/app/oracle/product/10.2.0

11. xargs command examples

Copy all images to external hard-drive
# ls *.jpg | xargs -n1 -i cp {} /external-hard-drive/directory
Search all jpg images in the system and archive it.
# find / -name *.jpg -type f -print | xargs tar -cvzf images.tar.gz
Download all the URLs mentioned in the url-list.txt file
# cat url-list.txt | xargs wget –c

12. ls command examples

Display filesize in human readable format (e.g. KB, MB etc.,)
$ ls -lh
-rw-r----- 1 ramesh team-dev 8.9M Jun 12 15:27 arch-linux.txt.gz
Order Files Based on Last Modified Time (In Reverse Order) Using ls -ltr
$ ls -ltr
Visual Classification of Files With Special Characters Using ls -F
$ ls -F

13. pwd command

pwd is Print working directory. What else can be said about the good old pwd who has been printing the current directory name for ages.

14. cd command examples

Use “cd -” to toggle between the last two directories
Use “shopt -s cdspell” to automatically correct mistyped directory names on cd

15. gzip command examples

To create a *.gz compressed file:
$ gzip test.txt
To uncompress a *.gz file:
$ gzip -d test.txt.gz
Display compression ratio of the compressed file using gzip -l
$ gzip -l *.gz
         compressed        uncompressed  ratio uncompressed_name
              23709               97975  75.8% asp-patch-rpms.txt

16. bzip2 command examples

To create a *.bz2 compressed file:
$ bzip2 test.txt
To uncompress a *.bz2 file:
bzip2 -d test.txt.bz2

17. unzip command examples

To extract a *.zip compressed file:
$ unzip test.zip
View the contents of *.zip file (Without unzipping it):
$ unzip -l jasper.zip
Archive:  jasper.zip
  Length     Date   Time    Name
 --------    ----   ----    ----
    40995  11-30-98 23:50   META-INF/MANIFEST.MF
    32169  08-25-98 21:07   classes_
    15964  08-25-98 21:07   classes_names
    10542  08-25-98 21:07   classes_ncomp

18. shutdown command examples

Shutdown the system and turn the power off immediately.
# shutdown -h now
Shutdown the system after 10 minutes.
# shutdown -h +10
Reboot the system using shutdown command.
# shutdown -r now
Force the filesystem check during reboot.
# shutdown -Fr now

19. ftp command examples

Both ftp and secure ftp (sftp) has similar commands. To connect to a remote server and download multiple files, do the following.
$ ftp IP/hostname
ftp> mget *.html
To view the file names located on the remote server before downloading, mls ftp command as shown below.
ftp> mls *.html -
/ftptest/features.html
/ftptest/index.html
/ftptest/othertools.html
/ftptest/samplereport.html
/ftptest/usage.html

20. crontab command examples

View crontab entry for a specific user
# crontab -u john -l
Schedule a cron job every 10 minutes.
*/10 * * * * /home/ramesh/check-disk-space

21. service command examples

Service command is used to run the system V init scripts. i.e Instead of calling the scripts located in the /etc/init.d/ directory with their full path, you can use the service command.
Check the status of a service:
# service ssh status
Check the steatus of all the services.
service --status-all
Restart a service.
# service ssh restart

22. ps command examples

ps command is used to display information about the processes that are running in the system.
While there are lot of arguments that could be passed to a ps command, following are some of the common ones.
To view current running processes.
$ ps -ef | more
To view current running processes in a tree structure. H option stands for process hierarchy.
$ ps -efH | more

23. free command examples

This command is used to display the free, used, swap memory available in the system.
Typical free command output. The output is displayed in bytes.
$ free
             total       used       free     shared    buffers     cached
Mem:       3566408    1580220    1986188          0     203988     902960
-/+ buffers/cache:     473272    3093136
Swap:      4000176          0    4000176
If you want to quickly check how many GB of RAM your system has use the -g option. -b option displays in bytes, -k in kilo bytes, -m in mega bytes.
$ free -g
             total       used       free     shared    buffers     cached
Mem:             3          1          1          0          0          0
-/+ buffers/cache:          0          2
Swap:            3          0          3
If you want to see a total memory ( including the swap), use the -t switch, which will display a total line as shown below.
ramesh@ramesh-laptop:~$ free -t
             total       used       free     shared    buffers     cached
Mem:       3566408    1592148    1974260          0     204260     912556
-/+ buffers/cache:     475332    3091076
Swap:      4000176          0    4000176
Total:     7566584    1592148    5974436

24. top command examples

top command displays the top processes in the system ( by default sorted by cpu usage ). To sort top output by any column, Press O (upper-case O) , which will display all the possible columns that you can sort by as shown below.
Current Sort Field:  P  for window 1:Def
Select sort field via field letter, type any other key to return

  a: PID        = Process Id              v: nDRT       = Dirty Pages count
  d: UID        = User Id                 y: WCHAN      = Sleeping in Function
  e: USER       = User Name               z: Flags      = Task Flags
  ........
To displays only the processes that belong to a particular user use -u option. The following will show only the top processes that belongs to oracle user.
$ top -u oracle

25. df command examples

Displays the file system disk space usage. By default df -k displays output in bytes.
$ df -k
Filesystem           1K-blocks      Used Available Use% Mounted on
/dev/sda1             29530400   3233104  24797232  12% /
/dev/sda2            120367992  50171596  64082060  44% /home
df -h displays output in human readable form. i.e size will be displayed in GB’s.
ramesh@ramesh-laptop:~$ df -h
Filesystem            Size  Used Avail Use% Mounted on
/dev/sda1              29G  3.1G   24G  12% /
/dev/sda2             115G   48G   62G  44% /home
Use -T option to display what type of file system.
ramesh@ramesh-laptop:~$ df -T
Filesystem    Type   1K-blocks      Used Available Use% Mounted on
/dev/sda1     ext4    29530400   3233120  24797216  12% /
/dev/sda2     ext4   120367992  50171596  64082060  44% /home

26. kill command examples

Use kill command to terminate a process. First get the process id using ps -ef command, then use kill -9 to kill the running Linux process as shown below. You can also use killall, pkill, xkill to terminate a unix process.
$ ps -ef | grep vim
ramesh    7243  7222  9 22:43 pts/2    00:00:00 vim

$ kill -9 7243

27. rm command examples

Get confirmation before removing the file.
$ rm -i filename.txt
It is very useful while giving shell metacharacters in the file name argument.
Print the filename and get confirmation before removing the file.
$ rm -i file*
Following example recursively removes all files and directories under the example directory. This also removes the example directory itself.
$ rm -r example

28. cp command examples

Copy file1 to file2 preserving the mode, ownership and timestamp.
$ cp -p file1 file2
Copy file1 to file2. if file2 exists prompt for confirmation before overwritting it.
$ cp -i file1 file2

29. mv command examples

Rename file1 to file2. if file2 exists prompt for confirmation before overwritting it.
$ mv -i file1 file2
Note: mv -f is just the opposite, which will overwrite file2 without prompting.
mv -v will print what is happening during file rename, which is useful while specifying shell metacharacters in the file name argument.
$ mv -v file1 file2

30. cat command examples

You can view multiple files at the same time. Following example prints the content of file1 followed by file2 to stdout.
$ cat file1 file2
While displaying the file, following cat -n command will prepend the line number to each line of the output.
$ cat -n /etc/logrotate.conf
    1 /var/log/btmp {
    2     missingok
    3     monthly
    4     create 0660 root utmp
    5     rotate 1
    6 }

31. mount command examples

To mount a file system, you should first create a directory and mount it as shown below.
# mkdir /u01

# mount /dev/sdb1 /u01
You can also add this to the fstab for automatic mounting. i.e Anytime system is restarted, the filesystem will be mounted.
/dev/sdb1 /u01 ext2 defaults 0 2

32. chmod command examples

chmod command is used to change the permissions for a file or directory.
Give full access to user and group (i.e read, write and execute ) on a specific file.
$ chmod ug+rwx file.txt
Revoke all access for the group (i.e read, write and execute ) on a specific file.
$ chmod g-rwx file.txt
Apply the file permissions recursively to all the files in the sub-directories.
$ chmod -R ug+rwx file.txt

33. chown command examples

chown command is used to change the owner and group of a file. \
To change owner to oracle and group to db on a file. i.e Change both owner and group at the same time.
$ chown oracle:dba dbora.sh
Use -R to change the ownership recursively.
$ chown -R oracle:dba /home/oracle

34. passwd command examples

Change your password from command line using passwd. This will prompt for the old password followed by the new password.
$ passwd
Super user can use passwd command to reset others password. This will not prompt for current password of the user.
# passwd USERNAME
Remove password for a specific user. Root user can disable password for a specific user. Once the password is disabled, the user can login without entering the password.
# passwd -d USERNAME

35. mkdir command examples

Following example creates a directory called temp under your home directory.
$ mkdir ~/temp
Create nested directories using one mkdir command. If any of these directories exist already, it will not display any error. If any of these directories doesn’t exist, it will create them.
$ mkdir -p dir1/dir2/dir3/dir4/

36. ifconfig command examples

Use ifconfig command to view or configure a network interface on the Linux system.
View all the interfaces along with status.
$ ifconfig -a
Start or stop a specific interface using up and down command as shown below.
$ ifconfig eth0 up

$ ifconfig eth0 down

37. uname command examples

Uname command displays important information about the system such as — Kernel name, Host name, Kernel release number,
Processor type, etc.,
Sample uname output from a Ubuntu laptop is shown below.
$ uname -a
Linux john-laptop 2.6.32-24-generic #41-Ubuntu SMP Thu Aug 19 01:12:52 UTC 2010 i686 GNU/Linux

38. whereis command examples

When you want to find out where a specific Unix command exists (for example, where does ls command exists?), you can execute the following command.
$ whereis ls
ls: /bin/ls /usr/share/man/man1/ls.1.gz /usr/share/man/man1p/ls.1p.gz
When you want to search an executable from a path other than the whereis default path, you can use -B option and give path as argument to it. This searches for the executable lsmk in the /tmp directory, and displays it, if it is available.
$ whereis -u -B /tmp -f lsmk
lsmk: /tmp/lsmk

39. whatis command examples

Whatis command displays a single line description about a command.
$ whatis ls
ls  (1)  - list directory contents

$ whatis ifconfig
ifconfig (8)         - configure a network interface

40. locate command examples

Using locate command you can quickly search for the location of a specific file (or group of files). Locate command uses the database created by updatedb.
The example below shows all files in the system that contains the word crontab in it.
$ locate crontab
/etc/anacrontab
/etc/crontab
/usr/bin/crontab
/usr/share/doc/cron/examples/crontab2english.pl.gz
/usr/share/man/man1/crontab.1.gz
/usr/share/man/man5/anacrontab.5.gz
/usr/share/man/man5/crontab.5.gz
/usr/share/vim/vim72/syntax/crontab.vim

41. man command examples

Display the man page of a specific command.
$ man crontab
When a man page for a command is located under more than one section, you can view the man page for that command from a specific section as shown below.
$ man SECTION-NUMBER commandname
Following 8 sections are available in the man page.
  1. General commands
  2. System calls
  3. C library functions
  4. Special files (usually devices, those found in /dev) and drivers
  5. File formats and conventions
  6. Games and screensavers
  7. Miscellaneous
  8. System administration commands and daemons
For example, when you do whatis crontab, you’ll notice that crontab has two man pages (section 1 and section 5). To view section 5 of crontab man page, do the following.
$ whatis crontab
crontab (1)          - maintain crontab files for individual users (V3)
crontab (5)          - tables for driving cron

$ man 5 crontab

42. tail command examples

Print the last 10 lines of a file by default.
$ tail filename.txt
Print N number of lines from the file named filename.txt
$ tail -n N filename.txt
View the content of the file in real time using tail -f. This is useful to view the log files, that keeps growing. The command can be terminated using CTRL-C.
$ tail -f log-file

43. less command examples

less is very efficient while viewing huge log files, as it doesn’t need to load the full file while opening.
$ less huge-log-file.log
One you open a file using less command, following two keys are very helpful.
CTRL+F – forward one window
CTRL+B – backward one window

44. su command examples

Switch to a different user account using su command. Super user can switch to any other user without entering their password.
$ su - USERNAME
Execute a single command from a different account name. In the following example, john can execute the ls command as raj username. Once the command is executed, it will come back to john’s account.
[john@dev-server]$ su - raj -c 'ls'

[john@dev-server]$
Login to a specified user account, and execute the specified shell instead of the default shell.
$ su -s 'SHELLNAME' USERNAME

45. mysql command examples

mysql is probably the most widely used open source database on Linux. Even if you don’t run a mysql database on your server, you might end-up using the mysql command ( client ) to connect to a mysql database running on the remote server.
To connect to a remote mysql database. This will prompt for a password.
$ mysql -u root -p -h 192.168.1.2
To connect to a local mysql database.
$ mysql -u root -p
If you want to specify the mysql root password in the command line itself, enter it immediately after -p (without any space).

46. yum command examples

To install apache using yum.
$ yum install httpd
To upgrade apache using yum.
$ yum update httpd
To uninstall/remove apache using yum.
$ yum remove httpd

47. rpm command examples

To install apache using rpm.
# rpm -ivh httpd-2.2.3-22.0.1.el5.i386.rpm
To upgrade apache using rpm.
# rpm -uvh httpd-2.2.3-22.0.1.el5.i386.rpm
To uninstall/remove apache using rpm.
# rpm -ev httpd

48. ping command examples

Ping a remote host by sending only 5 packets.
$ ping -c 5 gmail.com

49. date command examples

Set the system date:
# date -s "01/31/2010 23:59:53"
Once you’ve changed the system date, you should syncronize the hardware clock with the system date as shown below.
# hwclock –systohc

# hwclock --systohc –utc