linux_Switching From Windows to Nix

via: http://www.tecmint.com/useful-linux-commands-for-newbies/

 

2. Command: lsblk

The “lsblk” stands for (List Block Devices), print block devices by their assigned name (but notRAM) on the standard output in a tree-like fashion.

root@tecmint:~# lsblk

NAME   MAJ:MIN RM   SIZE RO TYPE MOUNTPOINT
sda      8:0    0 232.9G  0 disk 
├─sda1   8:1    0  46.6G  0 part /
├─sda2   8:2    0     1K  0 part 
├─sda5   8:5    0   190M  0 part /boot
├─sda6   8:6    0   3.7G  0 part [SWAP]
├─sda7   8:7    0  93.1G  0 part /data
└─sda8   8:8    0  89.2G  0 part /personal
sr0     11:0    1  1024M  0 rom

The “lsblk -l” command list block devices in ‘list‘ structure (not tree like fashion).

root@tecmint:~# lsblk -l

NAME MAJ:MIN RM   SIZE RO TYPE MOUNTPOINT
sda    8:0    0 232.9G  0 disk 
sda1   8:1    0  46.6G  0 part /
sda2   8:2    0     1K  0 part 
sda5   8:5    0   190M  0 part /boot
sda6   8:6    0   3.7G  0 part [SWAP]
sda7   8:7    0  93.1G  0 part /data
sda8   8:8    0  89.2G  0 part /personal
sr0   11:0    1  1024M  0 rom

Note: lsblk is very useful and easiest way to know the name of New Usb Device you just plugged in, especially when you have to deal with disk/blocks in terminal.

3. Command: md5sum

The “md5sum” stands for (Compute and Check MD5 Message Digest), md5 checksum (commonly called hash) is used to match or verify integrity of files that may have changed as a result of a faulty file transfer, a disk error or non-malicious interference.

root@tecmint:~# md5sum teamviewer_linux.deb 

47790ed345a7b7970fc1f2ac50c97002  teamviewer_linux.deb

Note: The user can match the generated md5sum with the one provided officially. Md5sum is considered less secure than sha1sum, which we will discuss later.

4. Command: dd

Command “dd” stands for (Convert and Copy a file), Can be used to convert and copy a file and most of the times is used to copy a iso file (or any other file) to a usb device (or any other location), thus can be used to make a ‘Bootlable‘ Usb Stick.

root@tecmint:~# dd if=/home/user/Downloads/debian.iso of=/dev/sdb1 bs=512M; sync

Note: In the above example the usb device is supposed to be sdb1 (You should Verify it using command lsblk, otherwise you will overwrite your disk and OS), use name of disk very Cautiously!!!.

dd command takes some time ranging from a few seconds to several minutes in execution, depending on the size and type of file and read and write speed of Usb stick.

6. Command: history

The “history” command stands for History (Event) Record, it prints the history of long list of executed commands in terminal.

root@tecmint:~# history

 1  sudo add-apt-repository ppa:tualatrix/ppa
 2  sudo apt-get update
 3  sudo apt-get install ubuntu-tweak
 4  sudo add-apt-repository ppa:diesch/testing
 5  sudo apt-get update
 6  sudo apt-get install indicator-privacy
 7  sudo add-apt-repository ppa:atareao/atareao
 8  sudo apt-get update
 9  sudo apt-get install my-weather-indicator
 10 pwd
 11 cd && sudo cp -r unity/6 /usr/share/unity/
 12 cd /usr/share/unity/icons/
 13 cd /usr/share/unity

Note: Pressing “Ctrl + R” and then search for already executed commands which lets your command to be completed with auto completion feature.

(reverse-i-search)`if': ifconfig

7. Command: sudo

The “sudo” (super user do) command allows a permitted user to execute a command as the superuser or another user, as specified by the security policy in the sudoers list.

root@tecmint:~# sudo add-apt-repository ppa:tualatrix/ppa

Note: sudo allows user to borrow superuser privileged, while a similar command ‘su‘ allows user to actually log in as superuser. Sudo is safer than su.
It is not advised to use sudo or su for day-to-day normal use, as it can result in serious error if accidentally you did something wrong, that’s why a very popular saying in Linux community is:

“To err is human, but to really foul up everything, you need root password.”

9. Command: touch

The “touch” command stands for (Update the access and modification times of each FILE to the current time). touch command creates the file, only if it doesn’t exist. If the file already exists it will update the timestamp and not the contents of the file.

root@tecmint:~# touch tecmintfile

Note: touch can be used to create file under directory, on which the user has write permission, only if the file don’t exist there.

10. Command: chmod

The Linux “chmod” command stands for (change file mode bits). chmod changes the file mode (permission) of each given file, folder, script, etc.. according to mode asked for.

There exist 3 types of permission on a file (folder or anything but to keep things simple we will be using file).

Read (r)=4
Write(w)=2
Execute(x)=1

So if you want to give only read permission on a file it will be assigned a value of ‘4‘, for write permission only, a value of ‘2‘ and for execute permission only, a value of ‘1‘ is to be given. For read and write permission 4+2 = ‘6‘ is to be given, ans so on.

Now permission need to be set for 3 kinds of user and usergroup. The first is owner, then usergroup and finally world.

rwxr-x--x   abc.sh

Here the root’s permission is rwx (read, write and execute).
usergroup to which it belongs, is r-x (read and execute only, no write permission) and
for world is –x (only execute).

To change its permission and provide read, write and execute permission to owner, group and world.

root@tecmint:~# chmod 777 abc.sh

only read and write permission to all three.

root@tecmint:~# chmod 666 abc.sh

read, write and execute to owner and only execute to group and world.

root@tecmint:~# chmod 711 abc.sh

Note: one of the most important command useful for sysadmin and user both. On a multi-user environment or on a server, this command comes to rescue, setting wrong permission will either makes a file inaccessible or provide unauthorized access to someone.

11. Command: chown

The Linux “chown” command stands for (change file owner and group). Every file belongs to a group of user and a owner. It is used Do ‘ls -l‘ into your directory and you will see something like this.

root@tecmint:~# ls -l 

drwxr-xr-x 3 server root 4096 May 10 11:14 Binary 
drwxr-xr-x 2 server server 4096 May 13 09:42 Desktop

Here the directory Binary is owned by user “server” and it belongs to usergroup “root” where as directory “Desktop” is owned by user “server” and belongs to user group “server“.

This “chown” command is used to change the file ownership and thus is useful in managing and providing file to authorised user and usergroup only.

root@tecmint:~# chown server:server Binary

drwxr-xr-x 3 server server 4096 May 10 11:14 Binary 
drwxr-xr-x 2 server server 4096 May 13 09:42 Desktop

Note: “chown” changes the user and group ownership of each given FILE to NEW-OWNER or to the user and group of an existing reference file.

12. Command: apt

The Debian based “apt” command stands for (Advanced Package Tool). Apt is an advanced package manager for Debian based system (Ubuntu, Kubuntu, etc.), that automatically and intelligently search, install, update and resolves dependency of packages on Gnu/Linuxsystem from command line.

root@tecmint:~# apt-get install mplayer

Reading package lists... Done
Building dependency tree       
Reading state information... Done
The following package was automatically installed and is no longer required:
  java-wrappers
Use 'apt-get autoremove' to remove it.
The following extra packages will be installed:
  esound-common libaudiofile1 libesd0 libopenal-data libopenal1 libsvga1 libvdpau1 libxvidcore4
Suggested packages:
  pulseaudio-esound-compat libroar-compat2 nvidia-vdpau-driver vdpau-driver mplayer-doc netselect fping
The following NEW packages will be installed:
  esound-common libaudiofile1 libesd0 libopenal-data libopenal1 libsvga1 libvdpau1 libxvidcore4 mplayer
0 upgraded, 9 newly installed, 0 to remove and 8 not upgraded.
Need to get 3,567 kB of archives.
After this operation, 7,772 kB of additional disk space will be used.
Do you want to continue [Y/n]? y

root@tecmint:~# apt-get update

Hit http://ppa.launchpad.net raring Release.gpg                                           
Hit http://ppa.launchpad.net raring Release.gpg                                           
Hit http://ppa.launchpad.net raring Release.gpg                      
Hit http://ppa.launchpad.net raring Release.gpg                      
Get:1 http://security.ubuntu.com raring-security Release.gpg [933 B] 
Hit http://in.archive.ubuntu.com raring Release.gpg                                                   
Hit http://ppa.launchpad.net raring Release.gpg                      
Get:2 http://security.ubuntu.com raring-security Release [40.8 kB]   
Ign http://ppa.launchpad.net raring Release.gpg                                                  
Get:3 http://in.archive.ubuntu.com raring-updates Release.gpg [933 B]                            
Hit http://ppa.launchpad.net raring Release.gpg                                                                
Hit http://in.archive.ubuntu.com raring-backports Release.gpg

Note: The above commands results into system-wide changes and hence requires root password (Check ‘#‘ and not ‘$’ as prompt). Apt is considered more advanced and intelligent as compared to yum command.

As the name suggest, apt-cache search for package containing sub package mpalyer. apt-getinstall, update all the packages, that are already installed, to the newest one.

Read more about apt-get and apt-cache commands at 25 APT-GET and APT-CACHE Commands

13. Command: tar

The “tar” command is a Tape Archive is useful in creation of archive, in a number of file format and their extraction.

root@tecmint:~# tar -zxvf abc.tar.gz (Remember 'z' for .tar.gz)

root@tecmint:~# tar -jxvf abc.tar.bz2 (Remember 'j' for .tar.bz2)

root@tecmint:~# tar -cvf archieve.tar.gz(.bz2) /path/to/folder/abc

Note: A ‘tar.gz‘ means gzipped. ‘tar.bz2‘ is compressed with bzip which uses a better but slower compression method.

Read more about “tar command” examples at 18 Tar Command Examples

16. Command: cat

The “cat” stands for (Concatenation). Concatenate (join) two or more plain file and/or print contents of a file on standard output.

root@tecmint:~# cat a.txt b.txt c.txt d.txt abcd.txt

root@tecmint:~# cat abcd.txt
....
contents of file abcd
...

Note: “>>” and “>” are called append symbol. They are used to append the output to a file and not on standard output. “>” symbol will delete a file already existed and create a new file hence for security reason it is advised to use “>>” that will write the output without overwriting or deleting the file.

Before Proceeding further, I must let you know about wildcards (you would be aware of wildcard entry, in most of the Television shows) Wildcards are a shell feature that makes the command line much more powerful than any GUI file managers. You see, if you want to select a big group of files in a graphical file manager, you usually have to select them with your mouse. This may seem simple, but in some cases it can be very frustrating.

For example, suppose you have a directory with a huge amount of all kinds of files and subdirectories, and you decide to move all the HTML files, that have the word “Linux” somewhere in the middle of their names, from that big directory into another directory. What’s a simple way to do this? If the directory contains a huge amount of differently named HTML files, your task is everything but simple!

In the Linux CLI that task is just as simple to perform as moving only one HTML file, and it’s so easy because of the shell wildcards. These are special characters that allow you to select file names that match certain patterns of characters. This helps you to select even a big group of files with typing just a few characters, and in most cases it’s easier than selecting the files with a mouse.

Here’s a list of the most commonly used wildcards :

Wildcard			Matches
   *			zero or more characters
   ?			exactly one character
[abcde]			exactly one character listed
 [a-e]			exactly one character in the given range
[!abcde]		any character that is not listed
 [!a-e]			any character that is not in the given range
{debian,linux}		exactly one entire word in the options given

! is called not symbol, and the reverse of string attached with ‘!’ is true.

Read more examples of Linux “cat command” at 13 Cat Command Examples in Linux