Linux_commands.txt

Linux Commands:
----------------

    Internal Commands
    External Commands



    Basic commands in Linux:
    ------------------------
        sudo su narayanan - switch to current user
        pwd - present working directory
        ls - list files
        mkdir Asia Africa Europe America - All the listed folders will be created
        mkdir Asia/India/Mumbai - All the listed folders will be created inside one another
        mkdir -p Asia/India/Mumbai - Command will create Asia as parent directory and rest as child directories
        cd .. - Change to previous directory
        Absolute Path and Relative Path
        pushd
        popd
        mv source_path destination_path - Move source path to destination path
        rm - removes files
        rm -rf - Remove files and Directories
        more file_name.txt - Shows all the content
        less file_name.txt - Shows all the content inside like a file
        ls -l 
        ls -a
        ls -lt
        ls -ltr
        ls -ld
        df -hP - Show how much disk is used
        du -sh - Show how much disk is free
        chsh
        whatis - show whatis what?
        man - Shows the manual of a command
        date - Shows the date and time in UTC
        history - history shows what commands I have used in the history
        env - Shows environment variables
        export - Export exports the variable
        uname -r - Lists Linux Kernel Name and Version Number
        dmesg
        udevadm
        lspci - find out information about the PCI busses and devices connected to the PCI subsystem
        lsblk - Provides the Disk partition and size
        lscpu - CPU architecture
        lsmem --summary
        free -m 
        lshw
        tar -cf tar.tar file1 file2 file3
        ping 192.168.1.10
        cat >> /etc/hosts
        hostname - hostname of the machine
        curl
        cat /etc/resolv.conf
        nslookup www.google.com - DNS of the server
        traceroute www.google.com-  number of hops
        netstat -an | grep 80 | grep -i LISTEN
        netstat -a | more
        users
        useradd narayanan - Add a new user
        usermod narayanan - Modifies the user
        whoami - Shows the current user
        userdel narayanan - Deletes the user
        groupadd -g 1011 developer
        groupdel developer
        /etc/shadow
        chmod 400 file.pem - Sets permission to file
        chown ubuntu:ubuntu developer.txt - Change ownership
        systemctl start docker
        systemctl stop docker
        systemctl restart docker
        systemctl reload docker
        systemctl enable docker
        systemctl disable docker
        cat etc/fstab - Shows the UUID
        cat /etc/passwd - Shows the users and their encrypted password
        cat /etc/shadow - Shows the users and the ID's
        




        Linux Kernel:
        -------------

            - Memory Management
            - Process Management
            - Device Drivers
            - System calls and security

        Boot Process:
        -------------

            - BIOS POST
            - Boot Loader (GRUB2)
            - Kernel Initialization
            - INIT Process (SYSTEMD)

        Run Levels:
        -----------

         - Runlevel 5 - GUI
         - Runlevel 3 - Command Line

         runlevel 0 -> poweroff.target

            runlevel 1 -> rescue.target

            runlevel 2 -> multi-user.target

            runlevel 3 -> multi-user.target

            runlevel 4 -> multi-user.target

            runlevel 5 -> graphical.target

            runlevel 6 -> reboot.target



    File Types in Linux
    -------------------

    Files 
    Directories
    System Files
    Sockets
    Named Pipes
    
    Hard Link
    Symbolic Link or Symblink


    File System Hierarchy:
    ----------------------

        - /home
        - /opt   - Third party software
        - /mnt  - for mounting
        - /tmp   - For temporary data
        - /media - For USB drive, external media are mounted in media
        - /dev   - mouse and Keyboard
        - /bin  - basic programs and binaries
        - /etc  - configuration Files
        - /lib  - shared Libraries
        - /usr  - user software
        - /var  - variables data, logs and cached data


    Linux Package Management:
    -------------------------

    Yum Package Manager:
    ====================

        - yum repolist
        - yum provides scp
        - yum remove
        - yum update httpd
    

    Debian Package Manager:
    =======================

        - dpkg -i vscode.deb


    File Compression:
    =================
      
      - tar -cf tar.tar file1 file2 file3
      - bzip2
      - gzip
      - xz

      Uncompressing:
      ==============

        - bunzip2
        - gunzip
        - unxz

    Searching Files and Directories:
    ================================

        - locate city.txt
        - find /home/micheal -name city.txt
        - grep 'sample.txt'
        - grep -i capital city.txt
        - grep -r 'third line' city.txt
        - grep -w exam city.txt


    IO Redirection:
    ===============

     Standard Input
     Standard Output
     Standard Error

     
     Linux Accounts:
     ===============

        - cat /etc/passwd
        - cat /etc/group
        - username UID GID
        - id micheal
        - who
        - cat /etc/sudoers


    CronJobs:
    ---------

        - crontab -e
        - crontab -l