How To Exclude Directory While Compressing With Tar

Quite a handy and useful tip here. Several times, you want to compress files and folders but there might be cases when you want to compress your data excluding some of the directories. Tar command makes the process easier by providing us a exclusion switch.

I was actually backing up data I had downloaded in the remote server and wanted a copy of backup tar file in my system as well. But all those images that resided in the folders deep inside were not necessary for me. So all I did was something like below:

adm@RServ:~$ tar cvf backup.tar test --exclude=image*

The above command effectively excludes all the sub directories from testdirectory having the string image (eg. image, images, images_old in my case) and creates the backup.tar file. Moreover, the --exclude switch also co-operates the regular expressions so you can specify the regex to filter the directories. As an example, the command below excludes the directories a, b, c, d, and e while creating the tarball.

adm@RServ:~$ tar cvf backup.tar test --exclude=[a-e]

You can exploit this switch for ease several times in your daily works. I hope this helps :)


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Empty Trash From Command Line In Ubuntu

CLI is such a sexy piece so why bother using GUI, even for cleaning up your trash. In this post, you will see how you can empty trash in Ubuntu from command line.

The trash you see in GUI is nothing but just the view for the files deleted by users which are temporarily moved to the special location of user's home directory. For any user, the trash location is ~/.local/share/Trash/. That is, whatever a user deletes gets saved in this location.

samar@samar-Techgaun:~$ rm -rf ~/.local/share/Trash/

I hope this becomes useful :)


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Add Google Search Support In Gnome-Terminal

Gnome-terminal is my favorite thing in my system and recently I came to know that I could add google search support in gnome-terminal which is totally awesome. Ubuntu Tweak already includes the google search support but if you want google search in your terminal without the whole ubuntu tweak, you can follow this guide.

All you need to do is add the PPA and you can easily install the gnome-terminal with google search support. Fire up the terminal and enter the following commands:

sudo add-apt-repository ppa:tualatrix/personal
sudo apt-get update
sudo apt-get install gnome-terminal

Credits: Ubuntu Tweak


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Binary, Hex, Octal and Decimal Conversion Under Linux

Base conversions are easy with linux CLI. No need of fancy GUI-based calculator to perform base conversions when there is our favorite linux terminal.

We will be using bc, a calculator language that supports arbitrary precision numbers with interactive execution of statements. We will exploit the pipelining feature of shell and will let the bc process our query to convert the numbers from one base to other.

From binary to decimal

The syntax is obvious and we will follow the similar syntax for all the conversions. In this first example, we are converting the binary number 1101101 from input base binary to decimal(obase defaults to decimal unless specified).

samar@samar-Techgaun:~$ echo "ibase=2;1101101" | bc
109

From octal to decimal

samar@samar-Techgaun:~$ echo "ibase=8;1101101" | bc
295489

From Hexadecimal to decimal

samar@samar-Techgaun:~$ echo "ibase=16;A1F3DF" | bc
10613727

From N-base to decimal

All you need to do is provide the appropriate ibase value (eg. ibase=4 for 4-base to decimal conversion).

samar@samar-Techgaun:~$ echo "ibase=16;A1F3DF" | bc
10613727

As seen in all the examples above, the conversion to decimal numbers does not require you to specify the obase as obase defaults to decimal. The same thing applies for ibase i.e. ibase defaults to decimal base by default as seen in the examples below.

Now lets try some conversion with decimal numbers as the input base.

From decimal to binary

samar@samar-Techgaun:~$ echo "obase=2;109" | bc
1101101

From decimal to octal

samar@samar-Techgaun:~$ echo "obase=8;295489" | bc
1101101

From decimal to hexadecimal

samar@samar-Techgaun:~$ echo "obase=16;10613727" | bc
A1F3DF

From decimal to N-base

All you need to do is provide the appropriate obase value (eg. obase=4 for decimal to 4-base conversion).

samar@samar-Techgaun:~$ echo "obase=4;121" | bc
1321

Below are few more examples of base conversions to clarify the use of the command.

From binary to octal

samar@samar-Techgaun:~$ echo "ibase=2;obase=8;1111" | bc
17

From hexadecimal to binary

samar@samar-Techgaun:~$ echo "ibase=16;obase=2;AFBE" | bc
1010111110111110

I hope this is helpful ;-)


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Disable Guest Account Login In Ubuntu 12.04

Security is an important issue and I do not want anyone to access my machine, not even as the guest. Like almost every operating systems, I could see guest logon option in Ubuntu 12.04 which was turned on by default. This post provides the steps to enable or disable the guest account login in Ubuntu 12.04.

Fire up your terminal and type the following command:

samar@samar-Techgaun:~$ sudo nano /etc/lightdm/lightdm.conf

Now add a new line at the end containing the string as below:

allow-guest=false

Now reboot your system or type the following in your terminal:

samar@samar-Techgaun:~$ sudo /etc/init.d/lightdm restart

The guest account will no longer be active. If you want to enable the guest login again, just remove the line you added or change the value to true. I hope this helps :)


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How To Fix Bootmgr Missing In UNetBootin

Sometimes while working with the LiveUSBs using UNetBootin, you might face the issue that says the Bootmgr is missing and it also says, Press Ctrl + ALT + DELETE TO Restart. This post will help you to fix this particular issue.

First off, format your USB as a FAT32 since it happens commonly because your USB drive is formatted as NTFS and UNetBootin seems to have issues with NTFS filesystems. If formatting to FAT32 also does not work, then try formatting as FAT filesystem.

If you still get boot errors from USB, it is possible that the partition is not marked as active. Assuming you're on windows, you can use the diskpart tool to make the partition active. See the process below:

list disk

The above command will display the disks and their sizes as well. Choose the appropriate disk as below:

select disk 1

Replace the value 1 in above command to select the correct USB drive. Then again list the partitions but usually you can select the partition for USBs as below and then activate it:

select partition 1
active

The active command will mark the currently selected partition as active. Now reboot and enjoy booting from LiveUSB.


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How To Enable Native PDF Viewer In Firefox 15

Firefox 14 added a native HTML5 and javascript based PDF reader to read PDF files within the browser but it is disabled by default in Firefox 15 since it is not totally ready. If you don't mind few minor glitches, you can experience the native PDF viewer in Firefox 15 through about:config

Browser developers are integrating many functionalities in the browsers themselves. PDF viewer is no exception and Mozilla is still working for fully functional PDF viewer based on HTML5 and javascript which is called as pdf.js. Pdf.js is still in Beta phase and Mozilla has not declared it as 100% usable so it is disabled by default in firefox 15.

Type about:config in the URL bar (and ignore warning if it appears). Then search for pdfjs. A particular preference pdfjs.disabled will be listed on the search result whose value is by default set to true.

You will just need to double click on this preference row and it will be set to false. This will enable the native PDF viewer in Firefox 15.

You'll possibly have to restart your browser to see the effect in action.

I have been using the native PDF viewer and haven't faced any glitches or problem still. I hope this is helpful :)


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How To Search Manual Pages In Linux

Linux system consists of hundreds of binaries, several syscalls, and other stuffs that do have manual page. What if you want to locate or find the commands by searching through the manual pages? In this post, I am going to talk about one such useful command to search through the manual page names and short descriptions.

The command I am talking about is the apropos command. The best way to learn any linux command is to read its corresponding manual and go through the help (-h or --help) so lets poke through the help of apropos itself.

samar@Techgaun:~$ apropos -h
Usage: apropos [OPTION...] KEYWORD...

  -d, --debug                emit debugging messages
  -v, --verbose              print verbose warning messages
  -e, --exact                search each keyword for exact match
  -r, --regex                interpret each keyword as a regex
  -w, --wildcard             the keyword(s) contain wildcards
  -a, --and                  require all keywords to match
  -l, --long                 do not trim output to terminal width
  -C, --config-file=FILE     use this user configuration file
  -L, --locale=LOCALE        define the locale for this search
  -m, --systems=SYSTEM       use manual pages from other systems
  -M, --manpath=PATH         set search path for manual pages to PATH
  -s, --section=SECTION      search only this section
  -?, --help                 give this help list
      --usage                give a short usage message
  -V, --version              print program version

Mandatory or optional arguments to long options are also mandatory or optional
for any corresponding short options.

The --regex option is enabled by default.

Report bugs to cjwatson@debian.org.

Particularly, the -e switch is quite useful to filter out your search. See the example below:

samar@Techgaun:~$ apropos -e tar
bf_tar (1)           - shell script to write a tar file of a bogofilter direc...
bf_tar-bdb (1)       - shell script to write a tar file of a bogofilter direc...
git-tar-tree (1)     - Create a tar archive of the files in the named tree ob...
lz (1)               - gunzips and shows a listing of a gzip'd tar'd archive
mxtar (1)            - Wrapper for using GNU tar directly from a floppy disk
ptar (1)             - a tar-like program written in perl
tar (1)              - The GNU version of the tar archiving utility
tar (5)              - format of tape archive files
tgz (1)              - makes a gzip'd tar archive
uz (1)               - gunzips and extracts a gzip'd tar'd archive

Each command has its associated short description and the apropos command searches the short description section of appropriate manual page for the provided keyword. You can also specify the search keywords in the form of regular expression for more flexibility. I hope this command counts as useful one :)


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