Linux File Permission

What are file permissions ⁉️

File permissions play a crucial role in ensuring proper privacy and security.

Don't worry, I'll guide you through it step by step 🪜.

How do they work 💼?

Unlike Windows 🏴‍☠️, Linux❤️‍🔥 files cannot be executed directly. This is because file permissions must allow🥱 the execution of a file for it to be executed.

😮 File permissions prevent unauthorized access to sensitive files or directories and also ensure data privacy.

✌️ In short, without proper file permissions, file execution, access, and modification cannot occur.

Now, before we move into file permissions description🪘, let's understand the Linux roles 🍎.

🪴User Role

There are three roles or entities in the Linux system: user👤, group👥, and others🐿️.

Here is the brief overview👀:

👤User(u): The Individual user who owns the file, directory. The user is often the person🤵/guy👦 who creatd the file or directory and becomes the owner💼 of the file. The owner has the most extensive control🍷 over the it.

👥Group(g): Users in the same🤘 group as the file owner will have access to the file. To allow a specific set of users to access the file, you can add them to a group and grant access to that group. This way, only the users in that group will have access to the file. Group permisssions allow collaboration🤝 among users with the similar😎 access.

👪Others(o): Everyone else🦨 who has access to the system but isn't the owner or in the group associated with the file. Others include the general public📢.

All three users/entities will have three types of permissions🙌

💭Entities Permission

📕Read(r): Allows viewing the content of a file or listing the content of a directory. Read permission is represented by the "r" symbol😋. Read permission also has an octal value of 4. Octal value is another way↕️ of representing file permissions.

We will explore this further.

✍️Write(w): Allows modification of the file’s content or creating, deleting and renaiming within the directory😺. Write permission is represented by “w” symbol, it has an octal value of 2.

🏊‍♂️Execute(x): This enables running the file as a program or traversing a directory. Execute has octal value of 1.

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To summarize, there are three🥉 roles in a Linux system: 👤user, 👥group, and 👪others.

• The user is the owner👑 of the file or directory,
• Group consists of users who belong to the same group🎅 as the file owner,
• others refers to the general public📢.

Each of these users has three individual permissions: 📕Read, ✍️Write, and 🏊‍♂️Execute.

• Read permission allows the user to only read📖 the file, and it is represented by the octal value of 4.
• Write permission allows the user to modify🧘‍♂️ the file, and it is represented by the octal value of 2.
• Execute permission allows the user to execute🏃 a file or traverse a directory, and it is represented by the octal value of 1.

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These permissions are organized in a string of nine characters for each file or diectory🐙.

eg:

rw-r--r-- ([rw-] represents read and write permission for the owner), ([r--]and read only permission to the group) and ([r--]and read only permission to the others).

🌅Viewing file Permissions

To view the permissions of files and directories, you can use the ls command with the -l option🛩️. Here's an example:

    ls -l

The output will display file information, including permissions, ownership, group, size, modification date, and filename.

Here's a breakdown of what a typical ls -l output looks like:

-rw-r--r-- 1 scor32k scor32k 43 Sep 19 01:00 myfile_scor32k.txt

In this example:

• rw-r--r-- represents the permissions🐯.
• 1 indicates the number of hard links🖇️.
• user is the owner of the file👑.
• group is the group associated with the file👥.
• 43 is the file size🤌.
• Sep 19 01:00 is the modification date💍.
• myfile_scor32k.txt is the filename❣️.

You may be thinking🤔 but how -rw-r--r-- permission got attached🔒 to the file when we created it,

this is becase of UMASK.

UMASK🤧 ?

In simple terms, whenever we create a file or directory in a Linux system, the system assigns default permissions to the file or directory based on Linux itself👑.

Interesting! more🥸

The *********umask********* is generally set to 022. You can check that using umask command.

Notes: The default permission for a file is 666, and the default permission for a directory is 777.

The entire process is as follows:

😎When a user creates a file, it will have a default permission of 666. The 022 umask will then be subtracted from 666, resulting in a final permission of 644😎.

The user will have read and write permission(6=4+2), the group will have read permission(4), and others will also have read permission(4).

🌱You can also try this with a directory: 777 - 022 = 755.

👾Modifying file permissions

chown which stands for change file mode or change file permission command is used to modify the permissions.

Add execute permission to file.

chmod +x myfile.txt

This +x adds execute permission to the file.

-rwxr-xr-x 1 scor32k scor32k 43 Sep 19 01:00 myfile.txt

See the image below:

Remove Permission

chmod -x myfile.txt

• + is used to add permission.
• - is used to remove permission.

-rw-r--r-- 1 scor32k scor32k 43 Sep 19 01:00 myfile.txt

Give permission based on specifc role:

1. User/owner Permission

Add Permission

chmod u+x myfile.txt

Remove Permission

chmod u-x myfile.txt

1. Group Permisson

chmod g+x myfile.txt

1. The same goes for others(o). You can experiment with this.

Octal Mode in chmod

This is the advanced🎓 version of file permission manipulation🧘‍♀️. Here, we use numeric values to represent each permission types (read, write, execute).

• Read[r] = 4
• Write(w) = 2
• Execute(x) = 1

To set permissions using an octal value, we assign a three-digit number to each entity (user, group, others) based on the desired🤖 permission.

Note: The file or directory can max have 777 file permission, which means the user,group and others will have read, write, and execute permission resepectively🦆.

👾Modifying file permissions, Octal edition.

Before moving forward,

we need to remember that the permissions are just a combination of (4, 2, 1), and as per our requirements, we can alter this🐊.

Suppose we want to add read and execute permission to only the user and read permission to groups and others.

So🌿,

We use 1 as the octal value for execute, and for read, we use 4.

The combined value will be 544.

🤠Example 1:

Add read and execute permission to the user, and read permission to the group and others.

chmod 544 myfile.txt

To be precise devide the r-xr—r— into 3 blocks r-x r-- r--, this will clear your doubts.

Note: The - before permission is for the file type. - for file and d is for directory.

😃Example 2:

Suppose, we want to add read and write to user, write and execute to group and read to others.

user: read = 4, write = 2 ⇒ 4+2 ⇒ 6

group: write = 2, execute = 1 ⇒ 2+1 ⇒ 3

others: read = 4 ⇒ 4

chmod 634 myfile.txt

FU
If i take examples there will not be any end😀, you can play around with this.

🦾Changing file ownership

chown which stands for change ownership command is used to chnage the ownership of file or directory.

chown abhishek myfile.txt

• you my require root privelage.

🚇Changing file group Ownership

chgrp command will be used to chnage the file group.

chgrp geet myfile.txt

• add myfile.txt to group geet

Some tips🏖️

• Never use 777 → It’s a severe security risk and show be avoided.
• use ls -l → This displays detailed information about files and directories, including their permissions.
• use chmod
• Limit the global access
• umask matters a lot
• Review permissions regularly.

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If the article helps you, leave a like, follow, or anything 🙂.

You can follow me on LinkedIn, GitHub, Dev.to and hashnode.

Bye

Comments

[Jack]

Adding too many icons to your article makes it harder to read.

[Abhishek Pathak]

hey thanks for review,
will take care of this from now and wil try to update the blog.