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Theory

Absolute Path vs Relative Path in Linux/Unix

One of this blog follower asked us that whatâs the difference between absolute and relative path?

To understand this we have to know what is a path in Linux.

What is a path?

A path is a unique location to a file or a folder in a file system of an OS. A path to a file is a combination of / and alpha-numeric characters. What is an absolute path?

An absolute path is defined as the specifying the location of a file or directory from the root directory(/). In other words we can say absolute path is a complete path from start of actual filesystem from / directory.

Some examples of absolute path:

/var/ftp/pub
/etc/samba.smb.conf
/boot/grub/grub.conf

If you see all these paths started from / directory which is a root directory for every Linux/Unix machines.

What is the relative path?

Relative path is defined as path related to the present working directory(pwd). Suppose I am located in /var/log and I want to change directory to /var/log/kernel. I can use relative path concept to change directory to kernel

changing directory to /var/log/kernel by using relative path concept.

$ pwd/var/logcd kernel

Note: If you observe there is no / before kernel which indicates itâs a relative directory to present working directory.

Changing directory to /var/log/kernel using absolute path concept.

$ cd /var/log/kernel

Note: We can use an absolute path from any location where as if you want to use relative path we should be present in a directory where we are going to specify relative to that present working directory.

Examples of relative path and absolute path for the same operation.

Basic Linux Command

help

Man: an interface to the on-line reference manuals

$ man ls

Wildcard

Show all picture (multiple char)

$ ls pic* ? show only picture between 50 and 59 (only one char) $ ls pic5?.jpg [] show only if char in [p-P] $ ls [pP]ic*

Files and directory

ls: list directory contents

$ ls

args = -l -a -r -t -h --help

Pwd: output the current working directory

$ pwd

Change directory

$ cd back to previous folder $ cd -

Make directory

$ mkdir test1 test2 test3

$ mkdir -p lol/lol/lol
-p to create parent directory if needed

Remove directory

rmdir filename

rm -rf file name

Move directory (can be used to rename a file)

mv file /opt/movedfile

Copy file or directory

$ cp file /opt/newcopiedfile

Touch - change file timestamps but it can also create files

$ touch nomdefichier.md $ touch pic{00..99}.jpeg # does not work

Which: Searching the PATH for executable files matching the names of the arguments

$ which ls

File: file — determine file type

$ file myfile

file viewer

More: file perusal filter for crt viewing

$ more filename

Less: opposite of more but Less is more ;)

$ less filename

Cat: concatenate files and print on the standard output

$ cat filename

Users and privileges

adduser, addgroup - add a user or group to the system

sudo adduser steve

r4v3n@d3bi4n:~/Workspace/test$ sudo adduser steve
[sudo] password for r4v3n: 
Sorry, try again.
[sudo] password for r4v3n: 
Adding user `steve' ...
Adding new group `steve' (1002) ...
Adding new user `steve' (1002) with group `steve' ...
Creating home directory `/home/steve' ...
Copying files from `/etc/skel' ...
New password: 
Retype new password: 
passwd: password updated successfully
Changing the user information for steve
Enter the new value, or press ENTER for the default
	Full Name []: 
	Room Number []: 
	Work Phone []: 
	Home Phone []: 
	Other []: 
Is the information correct? [Y/n] y

user skeleton: skeleton files used for new user configuration

$ ls /etc/skel/

─r4v3n at d3bi4n in /etc/skel
╰─» ls -a                                                                        0 (0.002s) < 05:21:24
./  ../  .bash_logout  .bashrc  .profile

Change user

$ su - marie

Permissions

Chmod: change file mode bits

A combination of the letters ugoa controls which users' access to the file will be changed:

the user who owns it (u),
other users in the file's group (g),
other users not in the file's group (o),
or all users (a).

If none of these are given, the effect is as if (a) were given, but bits that are set in the umask are not affected.

marie@d3bi4n:~$ ls -l
total 4
-rw-r--r-- 1 marie marie 12 Apr  7 05:44 test

$ chmod o-r mysecret

-rw-r----- 1 marie marie 12 Apr 7 05:44 test

$ chmod o+rw myscret

-rw-r--rw- 1 marie marie 12 Apr 7 05:44 test

###groups

Groups: print the groups a user is in

$ groups

Adds user marie into steve group

$ adduser marie steve

r4v3n@d3bi4n:~/Workspace/test$ sudo adduser marie steve
Adding user `marie' to group `steve' ...
Adding user marie to group steve
Done.

marie@d3bi4n:~$ groups
marie steve

Sysadmin tools

Htop: Interactive processes viewer

$ htop

text editor

Nano: Nano's ANOther editor, an enhanced free Pico clone (simple text editor for noobies)

$ nano

$ nano filename

VIM: vim - Vi IMproved, a programmer's text editor (PGM)

$ vim

$ vim filename

APT

$ apt install $ apt remove $ apt autoremove $ apt update

Display & Destop Manager

Architecture:

BIOS -> GRUB -> Display Manager -> Desktop Environement

Install Desktop Environement (GUI)

$ tasksel $ apt install gnome $ apt remove gnome

Reconfigurer le display manager

$ sudo dpkg-reconfigure gdm3

Installer le display manager

$ sudo apt install lightdm

$ sudo apt install gdm3

remove Desktop environement

$ sudo apt remove lightdm

Services

HTOP
dhclient > get ip
gnome networkmanager
wpa_supplicant > encryption @ wifi

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