🔒 Understanding Linux File Permissions and Ownership 🔒

Hey there, fellow tech enthusiasts! Today, we're going to dive into the intriguing world of Linux File Permissions and Ownership. 🐧

So, what's all this fuss about permissions and ownership? In Linux, every file and directory comes with a set of access rights that determine who can do what with it. These access rights are categorized into three groups:

1. Owner 👑: The owner of the file or application. This is the individual who created the file or the user who currently holds it.

2. Group 🤝: The group that owns the file or application. Groups allow multiple users to share common permissions on files, making it easier to manage access.

3. Others 🌍: Everyone else on the system who is not the owner or part of the group. These users have the least privileged access.

   Now, let's get hands-on and play with some commands! 😎

   Changing Ownership and Group 🧑‍🤝‍🧑🧑‍👧‍👧

   Suppose we have a directory named "project_files" with its current owner as "Shubham" and group as "Trainwithshubham." Now, we want to change the ownership to "Ashok" and the group to "Explorewithashok."

    $ ls -l project_files
    drwxr-xr-x 3 Shubham Trainwithshubham 4096 Jul 20 12:00 project_files
   
    $ sudo chown Ashok:Explorewithashok project_files
    $ ls -l project_files
    drwxr-xr-x 3 Ashok Explorewithashok 4096 Jul 20 12:00 project_files
   

   Now, "Ashok" is the owner, and "Explorewithashok" is the new group for the "project_files" directory.

   😎 Group Permission: The group refers to a collection of users who share common access rights to the file. When a file is created, it inherits the group of the user who created it. The chgrp command is used to change the group ownership of a file:

    chgrp new_group file.txt
   

   To change permissions for the owner, group, and others simultaneously, we can use a shorthand notation with chmod. For instance:

    chmod u=rw,g=r,o=r file.txt
   

   This command grants read and write permissions to the owner, read permissions to the group, and read permissions to others.

   Changing Permissions Numerically

   Suppose we have a script called "my_script.sh" with the following permissions:

    $ ls -l my_script.sh
    -rwxr-xr-- 1 sana group3 1024 Jul 20 14:30 my_script.sh
   

   We want to give the owner full access, the group read and execute permissions, and others no permissions.

    $ chmod 750 my_script.sh
    $ ls -l my_script.sh
    -rwxr-x--- 1 sana group3 1024 Jul 20 14:30 my_script.sh
   

   Now, the owner has read, write, and execute permissions (7), the group has read and execute permissions (5), and others have no permissions (0).

   Here's the breakdown of the numeric codes:

   • 7 (Owner): Read (4) + Write (2) + Execute (1)

   • 5 (Group): Read (4) + Execute (1)

   • 0 (Others): (0)

Adding and Removing Permissions

You have a script named "my_script.sh," and you want to allow the owner to execute it and grant read and execute permissions to the group while removing all permissions from others.

    bashCopy code$ chmod u+x my_script.sh    # Add execute permission for the owner
    $ chmod g+rx my_script.sh   # Add read and execute permissions for the group
    $ chmod o-rwx my_script.sh  # Remove all permissions from others

Access Control Lists (ACL)

Let's say you have a shared directory called "shared_docs," and you want to give "user1" read-and-write access and "user2" read-only access to all files inside that directory.

    $ setfacl -m u:Shubham:rw shared_docs
    $ setfacl -m u:Ashok:r shared_docs

Now, "Shubham" can read and write any file inside "shared_docs," while "Ashok" can only read them.

Example 2: Suppose we have a file called "shared_file.txt" that should be accessible by multiple users and groups. Let's set specific ACL rules:

    bashCopy code$ ls -l shared_file.txt
    -rw-r--r-- 1 userD groupD 512 Jul 20 13:00 shared_file.txt

    $ setfacl -m u:userE:rw shared_file.txt  # User "userE" can read and write
    $ setfacl -m g:groupE:r shared_file.txt  # Group "groupE" can read

    $ getfacl shared_file.txt
    # file: shared_file.txt
    # owner: userD
    # group: groupD
    user::rw-
    user:userE:rw-      # specific user "userE" has read and write access
    group::r--
    group:groupE:r--    # specific group "groupE" has read access

Removing ACL Entries

You realize you mistakenly gave "Ashok" write access to "important_file.txt" using ACL. Let's fix that!

    $ setfacl -x u:Ashok important_file.txt

This command removes the ACL entry for "Ashok" on "important_file.txt," reverting them to the default permissions.

😎 Remember, understanding these concepts is vital for maintaining data security and access control on your system. So, keep exploring, and don't forget to have fun with those Linux commands! 🚀🐧💻

Happy hacking! 👩‍💻👨‍💻

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