Linux Concepts


Linux Commands 
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)



sudo usermod -s /bin/sh username
sudo usermod −aG docker ubuntu
sudo usermod -m -d /home/newuser newuser

sudo useradd arunjai
cat /etc/passwd
clear
sudo passwd arunjai
sudo useradd -s /sbin/nologin lalith
cat /etc/passwd
su arunjai
su lalith
su passwd lalith
sudo passwd lalith
su lalith
sudo usermod -s /bin/sh lalith
su lalith
cat /etc/group
groups ubuntu
sudo usermod -aG docker ubuntu
groups ubuntu
groups docker
getent group docker
sudo usermod -aG docker arunjai
getent group docker
cd /home/
ls /home
cd ..
su arunjai
sudo usermod -m -d /home/arunjai arunjai
sudo usermod -d /home/arunjai arunjai
sudo groupadd ramesh
cat /etc/group

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

sudo useradd arunjai					- Adds a new user named arunjai.
cat /etc/passwd    				- Displays the contents of the /etc/passwd file, which contains user account information.
sudo passwd arunjai    					- Sets or changes the password for the user arunjai.
sudo useradd -s /sbin/nologin lalith  - Adds a new user named lalith with the shell set to /sbin/nologin, preventing lalith from logging in interactively.
cat /etc/passwd    						- Displays the updated contents of the /etc/passwd file.
su arunjai    							- Switches to the user arunjai.
sudo passwd lalith    					- Sets or changes the password for the user lalith.
sudo usermod -s /bin/sh lalith    		- Changes the shell for the user lalith 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 arunjai    		- Adds the user arunjai to the docker group.
getent group docker     				- Retrieves and displays the updated docker group entry.
sudo usermod -m -d /home/arunjai arunjai   	- Moves the home directory of the user arunjai to /home/arunjai.
sudo usermod -d /home/arunjai arunjai 	- Sets the home directory of the user arunjai to /home/arunjai (the -m option moves the contents of the old home directory to the new one).
sudo groupadd ramesh   					- 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
sudo systemctl start nginx
sudo systemctl stop nginx
sudo systemctl status nginx
sudo systemctl enable nginx 	- Enable nginx in System startup

sudo ufw status
sufo ufw allow ssh
sudo ufw allow SSh
sudo ufw allow SSH
sudo ufw allow ssh
sudo ufw allow 'Nginx Full'
sudo ufw enable
sudo ufw status

ctrl l
cd /var/www/html
echo "helloworld"
sudo touch index.html
sudo echo "Helloworld" > index.html
sudo vi index.html
sudo rm index.html

sudo kill -9 process_ID 

echo "shivam" | sudo tee -a /var/www/html/index.html

Linux Filesystem Hierarchy