# Linux Basic Concepts

Linux Basic Commands

```basic
whoami   					        - Current user name
pwd    						        - Current working dir
cd    						        - Change dir
ls    						        - List file or folder
ls -lrt 					        - List file or folder with details
ls -a   					        - List hidden files
mkdir dirname   			        - Create a new directory
rmdir   					        - Remove the diretory
rm filename   				        - Remove file
rm -rf    					        - Remove direcory forcefully
cp file name /destination           - Copy filename to /desination directory
mv filename1 filename1   	        - Rename filename1 to filename2
mv source destination    	        - Move the file source to destination
mkdir -p    				        - Create subdirectory
touch filename   			        - Create empty file
cat filename    			        - Display the content of file
echo "hi"   				        - Print the "hi" in the terminal
man ls    					        - Display the manual
vi filename    				        - Open file with editor
apt install tree  			        - Install tree package
tree .  					        - List subdirectry
rm -f   					        - Force remove 
history   					        - Display the command history
history > history.txt   	        - Copy the history to notepad 
cat /etc/os-release   		        - About os information
uptime   					        - Provide information system running
apt update   				        - Update package lists (Debian/Ubuntu)
yum update   				        - Update package lists (RHEL/CentOS)

scp localfile username@remotehost:/path/to/remote/directory/

sudo useradd sunil					     - Adds a new user named sunil.
cat /etc/passwd    				         - Displays the contents of the /etc/passwd file, which contains user account information.
sudo passwd sunil    					- Sets or changes the password for the user sunil.
sudo useradd -s /sbin/nologin joe       - Adds a new user named lalith with the shell set to /sbin/nologin, preventing joe from logging in interactively.
cat /etc/passwd    						- Displays the updated contents of the /etc/passwd file.
su sunil    							- Switches to the user sunil.
sudo passwd joe    					    - Sets or changes the password for the user joe.
sudo usermod -s /bin/sh joe    		    - Changes the shell for the user joe to /bin/sh, allowing them to log in interactively.
cat /etc/group    				        - Displays the contents of the /etc/group file, which contains group account information.
sudo usermod -aG docker ubuntu     		- Adds the user ubuntu to the docker group, allowing them to run Docker commands without sudo.
groups ubuntu    						- Displays the groups the user ubuntu belongs to.
getent group docker     				- Retrieves and displays the docker group entry from the group database.
sudo usermod -aG docker sunil    		- Adds the user arunjai to the docker group.
getent group docker     				- Retrieves and displays the updated docker group entry.
sudo usermod -m -d /home/sunil sunil   	- Moves the home directory of the user sunil to /home/sunil.
sudo usermod -d /home/sunil sunil 	- Sets the home directory of the user sunil to /home/sunil (the -m option moves the contents of the old home directory to the new one).
sudo groupadd sai   					- Creates a new group named ramesh.
cat /etc/group  						- Displays the updated contents of the /etc/group file.
sudo init 6								- Reboots the system (init 6 is equivalent to a reboot).
scp -i /path/to/your-key.pem /path/to/local/file username@remote_host:/path/to/remote/directory
sudo apt update
sudo apt install ufw

sudo apt-get install nginx
sudo yum install nginx
sudo service nginx start
sudo service nginx stop
sudo service nginx restart
sudo service nginx status
 
sudo systemctl restart nginx                  -  Restarts the Nginx web server
sudo systemctl start nginx                    - Starts the Nginx web server
sudo systemctl stop nginx                     - Stops the Nginx web server
sudo systemctl status nginx                   -  Checks the current status of the Nginx service
sudo systemctl enable nginx 	              - Enable nginx in System startup

sudo ufw status                               - checks the Firewall rules (UFW) 
sufo ufw allow ssh                            - Enable the secure remote access via ssh
sudo ufw allow 'Nginx Full'                   - Enable http and https (80 *443) allow the traffice
sudo ufw enable                               - Enables the UFW firewall

ctrl l
cd /var/www/html
echo "helloworld"                            - Print terminal output has helloworld
sudo touch index.html                        - create the empty file html format
sudo echo "Helloworld" > index.html
sudo vi index.html                           - Editer text file change the content
sudo rm index.html                           - remove the files fromt the pwd
```

### **chmod - change the access permissions**

Each group of three characters define permissions for each *class*:

* ![](https://cdn.hashnode.com/res/hashnode/image/upload/v1723181392403/1c83343a-88da-45dd-9667-5a482e6d3af7.png align="center")
    
    **Example : chmod 744** myCV.sh
    
* chmod user=7, group =4 , other =4 myCV.sh
    

| # | Sum | rwx | Permission |
| --- | --- | --- | --- |
| 7 | 4(r) + 2(w) + 1(x) | rwx | read, write and execute |
| 6 | 4(r) + 2(w) | rw- | read and write |
| 5 | 4(r)+ 1(x) | r-x | read and execute |
| 4 | 4(r) | r-- | read only |
| 3 | 2(w) + 1(x) | \-wx | write and execute |
| 2 | 2(w) | \-w- | write only |
| 1 | 1(x) | \--x | execute only |
| 0 | 0 | \--- | none |

above example show **chmod 744**  
user - can read, write and execute  
group - can read only  
others - can also have read access

Linux Directories

![](https://cdn.hashnode.com/res/hashnode/image/upload/v1723182420615/1ec1e45c-a8f2-47e9-a22c-c29519aed2e4.png align="center")

| Windows | Linux | Description |
| --- | --- | --- |
| C:\\ | Root Directory (/) | The top-level directory-All other directories and files are contained within this root directory. |
| C:\\users | /home | Contains user directories. For example, /home/username is where a user's personal files and settings are stored. |
| C:\\Program Files | /etc | Configuration files for the system and installed applications. |
| C:\\Windows | /var | Variable data like logs, spool files, and databases. |
| %appdata% | /usr | User programs and data. Includes /usr/bin (binaries), /usr/lib (libraries), and /usr/share (shared data). |
| C:\\System32 | /bin | Essential command binaries. |
| C:\\System32 | /sbin | System binaries, used for system maintenance. |
| C:\\Windows\\Temp | /tmp | Temporary files. |
| C:\\Windows\\System32\\drivers | /dev | Device files. |
| C:\\System32\\Taskmgr.exe | /proc: | Virtual filesystem providing process and system information. |
| C:\\System32\\msinfo32.exe | /sys: | Virtual filesystem providing information about the kernel, devices, and other system information. |