Basic Terminal commands

Remarks#

How to exract tar.gz/bz2/tbz files :

If Your File Extension is .tar.gz (or .tgz) use this command

 tar xvzf file.tar.gz

• x: This tells tar to extract the files.

• v: This option will list all of the files one by one in the archive.

The “v” stands for “verbose.”

• z: The z option is very important and tells the tar command to

uncompress the file (gzip).

• f: This options tells tar that you are going to give it a file name

to work with.

** If Your File Extension is .tar.bz2 (or .tbz)**

The major difference between these two is that the z option has been replaced by the j option.

• j: This will decompress a bzip2 file.

Changing password of current user

To change password of current user just type:

sudo passwd

It will ask you to enter your current password:

[sudo] password for <user>:

And then you will be asked to enter new password:

Enter new UNIX password:

And finally you will be asked to re-enter your password:

Retype new UNIX password:

Note: By default, the keys you press at a command-line password prompt are not displayed at all. They are, however, still registered.

Adding new user

adduser command adds a user to the system. In order to add a new user type:

sudo adduser <user_name>

example:

sudo adduser tom

After typing the above command, you will be prompted to enter details about the new user, such as new password, user Full name, etc.

Below is the information that user will be asked to fill in order to add a new user:

Enter new UNIX password:
Retype new UNIX password:
passwd: password updated successfully
Changing the user information for tom
Enter the new value, or press ENTER for the default
    Full Name []: Test User
    Room Number []:
    Work Phone []:
    Home Phone []:
    Other []:
Is the information correct? [Y/n] y

!!

(read as bangbang) is a shortcut to repeat the last command entered in console. It is especially useful to run previous command with some changes

adduser tom

adduser: Only root may add a user or group to the system.

Oh snap, what now? Well you could retype the command with sudo in front or you could try

sudo !!

equivalent to sudo “previous command entered”

This is especially useful if the command you just typed is especially long.

It can also be used to change a part of previous commands

cd path/to/wrong/directory

With

!!:s/wrong/right/

Will do

cd path/to/right/directory

List files and folders

To list files and folders inside current directory, we use ls command:

user@host:/$ ls
bin  boot  cdrom  dev  etc  home  initrd.img  lib  lib64  lost+found  
media  mnt  opt  proc  root  run  sbin  srv  sys  tmp  usr  var  vmlinuz

ls prints folder structure in simple view, color coded by type. The Ubuntu default colors for ls are:

blue for directories, green for executable files, sky blue for linked files, yellow with a black background for devices, pink for image files, and red for archive files.

ls -la will print folder structure with additional info:

user@host:/$ ls -la
total 104
drwxr-xr-x  23 root root  4096 јул 25 12:40 .
drwxr-xr-x  23 root root  4096 јул 25 12:40 ..
drwxr-xr-x   2 root root  4096 јул 25 12:42 bin
drwxr-xr-x   4 root root  4096 јул 25 12:42 boot
drwxrwxr-x   2 root root  4096 јул 25 12:38 cdrom
drwxr-xr-x  16 root root  4300 јул 30 12:18 dev
drwxr-xr-x 134 root root 12288 јул 30 12:18 etc
drwxr-xr-x   5 root root  4096 јул 25 12:50 home
lrwxrwxrwx   1 root root    33 јул 25 12:40 initrd.img -> boot/initrd.img-3.19.0-39-generic
drwxr-xr-x  23 root root  4096 јул 25 12:42 lib
drwxr-xr-x   2 root root  4096 дец  9  2015 lib64
drwx------   2 root root 16384 јул 25 12:32 lost+found
drwxr-xr-x   3 root root  4096 јул 25 14:56 media
drwxr-xr-x   2 root root  4096 апр 11  2014 mnt
drwxr-xr-x   3 root root  4096 јул 25 13:37 opt
dr-xr-xr-x 227 root root     0 јул 30 12:18 proc
drwx------   2 root root  4096 јул 25 13:06 root
drwxr-xr-x  23 root root   780 јул 31 14:30 run
drwxr-xr-x   2 root root 12288 јул 25 12:46 sbin
drwxr-xr-x   2 root root  4096 дец  8  2015 srv
dr-xr-xr-x  13 root root     0 јул 30 12:18 sys
drwxrwxrwt   8 root root  4096 јул 31 16:05 tmp
drwxr-xr-x  10 root root  4096 дец  8  2015 usr
drwxr-xr-x  13 root root  4096 дец  9  2015 var
lrwxrwxrwx   1 root root    30 јул 25 12:40 vmlinuz -> boot/vmlinuz-3.19.0-39-generic

Another shortcut for ls -la is ll. However, this is not a builtin command. Rather its an alias common in ubuntu systems, in full its ls -laF. The alias will give you the same output as ls -la, but with additional slash (/) at the end of each folder, to help you with easier folder identification.

The ll alias can be viewed in full by typing alias ll. As illustrated below. If the alias is not set then the command will give an error.

vagrant@host ~ ->>
08:05 AM Mon Sep 12$ alias ll
 alias ll='ls -alF'

Restart Ubuntu

You can restart ubuntu from command line. Below is example of restarting ubuntu immediately.

 sudo reboot

You need to have sudo privilege in order to use this command.

Another commands with same results are sudo shutdown -r now and sudo init 6.

Install new software

APT and APT-GET

Easiest and fastest way is with apt-get command. This command may be considered as lower-level and “back-end”, and support other APT-based tools. There are no fancy loaders, only basic progress info. This is fastest way for installing apps.

Usage:

sudo apt-get install deluge openssh-server

This command will install two new apps: deluge and openssh-server. You can install as many apps as you want in only one line of commands.

“Fancy” way of the same process is wits apt:

sudo apt install deluge openssh-server

Result is the same, but interaction with users is different from previous command. apt is designed for end-users (human) and it’s output may be changed between versions.

Both commands will handle dependencies automatically.

user@host:~$ sudo apt install vlc
Reading package lists... Done
Building dependency tree       
Reading state information... Done
The following packages were automatically installed and are no longer required:
  libtimezonemap1 sbsigntool
Use 'apt-get autoremove' to remove them.
The following extra packages will be installed:
  libbasicusageenvironment0 libcddb2 libcrystalhd3 libdvbpsi8 libebml4
  libfreerdp1 libgnutls28 libgroupsock1 libhogweed2 libiso9660-8
  liblivemedia23 libmatroska6 libproxy-tools libresid-builder0c2a libsidplay2
  libssh2-1 libtar0 libupnp6 libusageenvironment1 libva-x11-1 libvcdinfo0
  libvlc5 libvlccore7 libxcb-composite0 libxcb-keysyms1 libxcb-randr0
  libxcb-xv0 vlc-data vlc-nox vlc-plugin-notify vlc-plugin-pulse
Suggested packages:
  firmware-crystalhd freerdp-x11 gnutls-bin videolan-doc
Recommended packages:
  libdvdcss2
The following NEW packages will be installed:
  libbasicusageenvironment0 libcddb2 libcrystalhd3 libdvbpsi8 libebml4
  libfreerdp1 libgnutls28 libgroupsock1 libhogweed2 libiso9660-8
  liblivemedia23 libmatroska6 libproxy-tools libresid-builder0c2a libsidplay2
  libssh2-1 libtar0 libupnp6 libusageenvironment1 libva-x11-1 libvcdinfo0
  libvlc5 libvlccore7 libxcb-composite0 libxcb-keysyms1 libxcb-randr0
  libxcb-xv0 vlc vlc-data vlc-nox vlc-plugin-notify vlc-plugin-pulse
0 upgraded, 32 newly installed, 0 to remove and 308 not upgraded.
Need to get 10,5 MB of archives.
After this operation, 51,7 MB of additional disk space will be used.
Do you want to continue? [Y/n] 

DPKG

dpkg stands for Debian Package. This is basic, low-level package installer for Debian and other Debian derivatives. dpkg have many options, but we are interested in -i, which stands for install.

sudo dpkg -i google-chrome-stable.deb

You can install .deb packages with dpkg.

If you get an error while installing .deb package, in most cases you don’t have some dependencies. To get rid of this error and install app correctly, run sudo apt-get -f install without any other parameter. This will search for dependencies and install them before .deb. Installation will continue and app will be installed.

Reading a text file

Using Ubuntu you have different ways to read a text file, all similar but useful in different context.

cat

This is the simplest way to read a text file; it simply output the file content inside the terminal. Be careful: if the file is huge, it could take some time to complete the printing process! If you need to stop it, you can always press CTRL+C. Note that if you need to navigate through the document, you need to scroll the terminal output.

cat file_name.txt

more

An improved version of cat. If your file is longer than the display of the terminal, you can simply type

more file_name.txt

and you’ll have a downwards scrolling display of text, in which you can move down by pressing ENTER.

less

This is the more command with some enhancements, and is typically a better choice than cat for reading medium to big documents. It opens file showing them from the beginning, allowing to scroll up/down/right/left using arrows.

less file_name.txt

Once the document is open, you can type some commands to enable some useful features, such as:

• q: close immediately the opened file.
• /word: search ‘word’ inside the document. Pressing n you can go to the following occurrence of ‘word’.
• ENTER: scrolls down of a single line.
• r: repaints the file content, if it’s changing while reading.

This is the best choice for reading medium to big documents.

tail

This software shows only the last part of the file. It’s useful if you need to read just a few lines in the end of a very big document.

tail file_name.txt

The above command will show last 10 lines(default) of the file. To read last 3 lines, we need to write:

tail -3 file_name.txt

There’s another use case where this command is extremely useful. Imagine to have a empty document, that is filled while you are watching it; if you want to see new lines in real time while they are written to the file without reopening it, just open the file with the -f option. It’s really useful if you are watching some logs, for example.

tail -f file_name.txt

This is the best choice for reading growing documents.

head

This command does the opposite task of tail. For example the following command will show the first 15 lines of the file file_name.txt.

head -15 file_name.txt

tailf

This is an alternative for tail -f filename .It follows the file changes as they occur and shows you the output.

vim

Some of us like vi, some others like vim. This is not just for reading files, you can also edit them! Now let’s see only some features that regards reading documents. Please note that vim offers syntax highlighting.

vim file_name.txt

Once the file is opened, be careful! Don’t start typing, or you will mess everything up! In fact, even if you can see the cursor, you have to press i to start typing and ESC after you finished typing. By the way, now I’m going to showing you some useful commands that concern reading (not writing):

• : : you need to type colon before inserting each of the following commands!
• q! : exit from the file without asking a confirm. It’s the same as q if you didn’t edit the text.
• /word : search for ‘word’ inside the document.
• 230 : goes to line ‘230’.

Tip: a shortcut to insert a colon and then type wq! for writing edits to file and quit without asking a confirm, you can hold down SHIFT and press twice z.

This is the best choice for reading code files.

Search the exact name of a packet for apt-get

If you know you need a packet <packet>, but you don’t know the exact name <packet-exact-name>, instead of searching with Google try with the following:

sudo apt-get update
apt-cache search <packet>

This will return you a list of packets name with a description. Once you have identified the exact packet name <packet-exact-name> install it normally:

sudo apt-get install <packet-exact-name>

Limit output to lines with the desired string

If you are running a command that returns hundreds of lines, but your interest is just on the lines that contains the word <word>, you should definitely use grep! For example try running:

ifconfig -a

Check the output, that could be only a few lines or quite long, if you have a server with multiple network interfaces. To show (for example purpose) only the lines that contain ‘HWaddr’, try using grep:

ifconfig -a | grep HWaddr

Now the output should be much shorter! Generally speaking, you could use grep in the following way:

<command-with-output> | grep <word>

Compress files and folders using the tar command

Use the tar (tape archive) command to compress your files and folders. It is similar to creating .ZIP files in Windows environment.

Syntax: tar -zcvf <output tar file> <source file> 

Example: tar -zcvf outputfile.tar.gz source file

Here’s what those switches actually mean:

-c: Create an archive.
-z: Compress the archive with gzip.
-v: Display progress in the terminal while creating the archive, also known as “verbose” mode. The v is always optional in these commands, but it’s helpful.
-f: Allows you to specify the filename of the archive.