# Day 2 : Basics of Linux

**Day2: Introduction to Linux**

**What is Linux?**

1. Linux is an open-source operating system, It is a freely available operating system that can be installed on a wide range of devices such as desktops, servers, smartphones and tablets, supercomputers etc.
    
2. An operating system (OS) is a system of software that manages computer hardware, software resources and provide common services for computer programs.
    

**Linux File System Hierarchy - In L**inux everything is represented as a file including a hardware program the files are stored in a directory and every directory contains a file with a tree structure that is called file system hierarchy.

1. **/home** - It creates home directory for other user.
    
2. **/root** - home directory for root user.
    
3. **/boot** - It contains bootable files for linux.
    
4. **/etc** - Contains all configuration files.
    
5. **/user** - By default software is installed in this directory.
    
6. **/bin** - It contains command used by all users.
    
7. **/sbin** - It contains command used by only root user.
    
8. **/opt** - Optional application software packages.
    
9. **/dev** - Essential device files.
    
10. **/mnt** - Temporarily mounted file systems.
    

**Features of Linux**

1. Open source
    
2. Secure
    
3. Simplified updates for all installed software.
    
4. Light weight
    
5. Multiple Distribution(Fedora,Debian,RedHat)
    

**Basic Linux Commands**

* / Is your root directory.
    
* ~ Is your home directory.
    
* uname : It show name of kernal (OS).
    
* uname -r : It show version of kernal.
    
* clear : Is use for clear screen.
    
* whoami : It shows currently login user name.
    
* date : It shows time and date.
    
* cal : Show this month's calendar
    
* history : It show list of previously used command.
    

```bash
ubuntu@ip-172-31-205-241:~$ uname
Linux
ubuntu@ip-172-31-205-241:~$ uname -r
5.15.0-1028-aws
ubuntu@ip-172-31-205-241:~$ date
Mon Mar 27 11:59:37 UTC 2023
```

1. **ls** - The most frequently used command in Linux to list directories
    
2. **pwd** - Print working directory command in Linux
    
3. **cd** - Linux command to navigate through directories
    
4. **mkdir** - Command used to create directories in Linux
    
5. **cd ..** - Change the directory to one step back.
    
6. **cd ../..** - Change directory to 2 lavels back.
    
7. **mv** - Move or rename files in Linux
    
    ```bash
    ubuntu@ip-172-31-205-241:~$ whoami ubuntu 
    ubuntu@ip-172-31-205-241:~$ touch my_file.txt 
    ubuntu@ip-172-31-205-241:~$ ls 
    my_file.txt 
    ubuntu@ip-172-31-205-241:~$ pwd
    /home/ubuntu 
    ubuntu@ip-172-31-205-241:~$ mkdir linux 
    ubuntu@ip-172-31-205-241:~$ ls 
    linux my_file.txt 
    ubuntu@ip-172-31-205-241:~$ cd linux 
    ubuntu@ip-172-31-205-241:~/linux$ pwd 
    /home/ubuntu/linux 
    ubuntu@ip-172-31-205-241:~/linux$ cd .. 
    ubuntu@ip-172-31-205-241:~$ ls 
    linux my_file.txt 
    ubuntu@ip-172-31-205-241:~/linux$ mv ../my_file.txt .
    ubuntu@ip-172-31-205-241:~/linux$ ls
    my_file.txt
    ```
    
    ### **Listing commands**
    
    **ls** - The most frequently used command in Linux to list directories
    
    **ls -a** - you can see the whole list of files, including the hidden files.
    
    **ls -l** - The ls command will only display the files.
    
    **ls -d \*/ -** If you only want to display the sub-directories excluding all other files, you can use this command
    
    **ls -g -** If you don't want to display the owner information in your list
    
    **ls -lg -** f you don't want to display the group information in your list
    
    **ls ../ -** This command contains the list of the parent directory.
    

**Linux Command to Create a Nested Directory :**

command to create a nested directory is : mkdir -p A/B/C/D/E

<mark>-p</mark> is for no error if existing, make parent directories as needed

<mark>tree</mark> command is used to show the nested directory.

```bash
ubuntu@ip-172-31-205-241:~$ mkdir -p A/B/C/D/E 
ubuntu@ip-172-31-205-241:~$ tree
.
├── A
│   └── B
│       └── C
│           └── D
│               └── E
├── dir
│   ├── dir1
│   └── dir2
├── linux
│   ├── linux
│   └── my_file.txt
└── snap
    └── tree
        ├── 18
        ├── common
        └── current -> 18
14 directories, 2 files
```

Thanks For Regarding\*! :)\*

Pooja Patil