How to get the serial number of your network device in linux?

1. sudo lshw -C network | grep -i serial
    lshw    - Command used to list the details of all available hardware in a system.
    -C      - Option used to specify hardware "class".
        network - We asked "lshw" to list only the network devices.

    grep    - Command used to print lines that matches the given pattern
    -i    - Option used to ignore case sensitivity
    serial    - Pattern used to fetch the lines that contains the word "serial"

Example:
$sudo lshw -C network | grep -i serial
[sudo] password for :
       serial: 78:f2:9e:f3:88:e7
   
2. /sbin/ifconfig | grep -i hwaddr or sudo ifconfig | grep -i hwaddr
    ifconfig-Command used to configure network devices.
    grep    - Command used to print lines that matches the given pattern
    -i    - Option used to ignore case sensitivity
    serial    - Pattern used to fetch the lines that contains the word "serial"


Example:
$/sbin/ifconfig | grep -i hwaddr
eth0      Link encap:Ethernet  HWaddr 78:f2:9e:f3:88:e7  

3. GUI Way
Applications -> System Tools -> Settings

                                  You will land in the following screen

Settings panel

Click on Network the following window will be open

Network settings panel

The green highlighted part is our interest.

6 often needed sed scripts for string processing

1. How to remove all empty lines in a file
  sed -e '/^$/d' filename.txt

2. How to remove the leading empty spaces
  (whitespace only) -> sed -e 's/^[ ]*//' /file/path/filename.txt
  (whitespace and tab \t) -> sed -e 's/^[ \t]*//' /file/path/filename.txt

3. How to add some string to starting of all lines of a file
  sed -e 's/^/string-to-add-at-starting/g' /file/path/filename.txt

4. How to add date to starting of all lines
  sed -e "s/^/$(date) /g" /file/path/filename.txt  - Note: The Double quotes.
  Before    ->    line in a file
  After    ->    Thu May  4 17:31:58 IST 2017 line in a file

5. How to add formatted date to starting of all lines
  sed -e "s/^/$(date '+%m\/%d\/%Y %H:%M:%S') /g" /file/path/filename.txt
  Example:
   Before    ->    line in a file
   After    ->    05/04/2017 17:30:50 line in a file

6. How to do multiple replace at one go
  sed -e 's/string-to-find1/string-to-replace1/g' -e 's/string-to-find2/string-to-replace2/g' /file/path/filename.txt

Some More scripts:
7. How to remove all contents after pattern match
  sed -e '/pattern/,$d' /path-to/file/filename.txt
  For Ex: To remove all contents after first empty line -> sed -e '/^$/,$d'


8. How to remove all contents before pattern match
  sed -e '0,/pattern/d' /path-to/file/filename.txt
  For Ex: To remove all contents before first empty line -> sed -e '0,/^$/d'

How to create printable version of a man page..?

Most of us are always feel boring to read man pages in terminal window. what if we have a printable version of a particular command's manpage.? Nice isn't it.. so, how we can create a printable version of a manpage...

Step 1: Issue the following command in terminal
$man -t > destination_file_path.ps

Ex:$man -t mkdir > ~/Desktop/mkdir_manpage_printableversion.ps

Now you got a file named " mkdir_manpage_printableversion.ps " in your Desktop :). you can now print and use it..

Note: .ps(Postscript) is the default file type used to print.  It can be opened with any PDF viewer and can be printed.

How to edit/Modify/Delete Bookmarks in vinagre?

Vinagre bookmarks are stored in the file vinagre-bookmarks.xml file under /home//.local/share/vinagre directory.

As all the bookmarks are stored in single line be bit more cautious before editing, otherwise you will endup mess.
(I Recommend to keep a backup of the file before editing)

All the bookmarks are starts and ends with & xml node.  So as per your wish do edit/modify the Bookmarks.

Example entry in vinagre-bookmarks.xml file: <item><item><protocol>vnc</protocol><name>Asset-Mgmt-Client-1</name> <host>10.184.48.82</host><username></username><port>5915</port> <fullscreen>0</fullscreen><width>800</width><height>600</height> <view_only>0</view_only><scaling>0</scaling><keep_ratio>1</keep_ratio> <depth_profile>0</depth_profile><lossy_encoding>0</lossy_encoding></item>

How to fix/suppress "apache2: Could not reliably determine the server's fully qualified domain name, using 127.0.1.1." warning message?

Warning message Before the fix:

"apache2: Could not reliably determine the server's fully qualified domain name, using 127.0.1.1. Set the 'ServerName' directive globally to suppress this message"


Fix: 
execute the following command in terminal

echo "ServerName localhost" | sudo tee -a /etc/apache2/apache2.conf

Now restart apache server by executing the following command

sudo /etc/init.d/apache2 restart


Message after the fix:
[ ok ] Restarting web server: apache2.

How to resolve "no suitable module for running kernel found" error in virtualbox instalation in debian linux?

1. Check wheather you machine is installed with "linux-headers-, linux-image-"
by issueing the follwing command in terminal.

  $dpkg -l | grep linux

In my case my kernel version is "3.16.0-4-686-pae" so the output of the above command would be something like as follows, 

Missing linux headers package

If you don't find any linux-headers or linux-images then you must install them first.

2. To find the your kernel version use the following command
  $uname -a

[ My output -> Linux hostname 3.16.0-4-686-pae #1 SMP Debian 3.16.36-1+deb8u2 (2016-10-19) i686 GNU/Linux ]

now install the required packages specified in step 1.

3.  Uninstall your previous virutalbox package and reinstall it.

  $sudo apt-get remove --purge virtualbox
  $sudo apt-get instlal virtualbox

4.  Restart you machine.