How to Set File Permissions in Linux

Last Updated : 06 Mar, 2025

Ever worried about who can access, modify, or execute your critical files on a Linux system? File permissions are the backbone of Linux security, ensuring that only authorized users and processes interact with your data.

In this guide, you’ll learn how to master Linux file permissions using commands like chmod, chown, and chgrp. We’ll break down the basics of read, write, and execute privileges, decode symbolic and octal notation (like 755 or rwxr-xr–), and walk through real-world examples from securing sensitive config files to granting access to collaborators. Avoid common pitfalls like overly permissive directories or misconfigured ownership, and discover best practices to keep your system safe and efficient.

What are File Permissions in Linux

In Linux, file permissions are rules that determine who can access, modify, or execute files and directories. They are foundational to Linux security, ensuring that only authorized users or processes can interact with your data. Here’s a breakdown:

1. The Three Basic Permissions

Every file or directory has three types of permissions:

Read (r): View the file’s contents or list a directory’s files.
Write (w): Modify a file or add/delete files in a directory.
Execute (x): Run a file as a program/script or enter a directory.

Letters	Definition
‘r’	“read” the file’s contents.
‘w’	“write”, or modify, the file’s contents.
‘x’	“execute” the file. This permission is given only if the file is a program.

2. Ownership and Permission Groups

Permissions are assigned to three categories of users:

User (Owner): The person who created the file.
Group: Users belonging to a shared group (e.g., “developers” or “admins”).
Others: Everyone else on the system.

File Permission: Operation Chart

Operators	Definition
`+`	Add permissions
`-`	Remove permissions
`=`	Set the permissions to the specified values

Note: All these permissions are being granted at three different levels based on their group.

What are Permission Groups in Linux

First, you must think of those nine characters as three sets of three characters (see the box at the bottom). Each of the three “rwx” characters refers to a different operation you can perform on the file.

Owners: These permissions apply exclusively to the individuals who own the files or directories.
Groups: Permissions can be assigned to a specific group of users, impacting only those within that particular group.
All Users: These permissions apply universally to all users on the system, presenting the highest security risk. Assigning permissions to all users should be done cautiously to prevent potential security vulnerabilities.

---     ---     ---
rwx     rwx     rwx
user    group   other

User, Group, and others Option in Linux File Permission

Reference	Class	Description
`u`	user	The user permissions apply only to the owner of the file or directory, they will not impact the actions of other users.
`g`	group	The group permissions apply only to the group that has been assigned to the file or directory, they will not affect the actions of other users.
`o`	others	The other permissions apply to all other users on the system, this is the permission group that you want to watch the most.
`a`	All three	All three (owner, groups, others)

How to Check the Permission of Files in Linux

Let’s dive in to understand the possible methods to check all the desired details of a file including “File Permission”

1. The “Trusty Command”

Here’s the command to execute it within the terminal. Let’s show you with an example:

Input:

We’re taking ‘NarX’ as a default file name:

ls -l NarX.txt

Output:

-rw-r--r-- 1 user group 46 Apr 14 16:37 NarX.txt

The above command represents these following information:

The first character = ‘-‘, which means it’s a file ‘d’, which means it’s a directory.
The next nine characters = (rw-r–r–) show the security
The next column shows the owner of the file.
The next column shows the group owner of the file. (which has special access to these files)
The next column shows the size of the file in bytes.
The next column shows the date and time the file was last modified.

2. The ‘namei’ Command

The ‘namei’ command is used to check the file path through layer of folder’s path. Here’s the command to execute it within Terminal:

Here, we’ve taken ‘path’ as ” root@anonymous-VirtualBox:~# ” and file name as “hoops”

namei -l /path/to/your/file

3. The ‘stat’ Command

Unlike ‘ls -l’ command, the “stat” command is used to pin point the file location. Here’s how you can do it:

We’re taking file name as “hoops”

stat hoops

Output:

  File: example.txt
  Size: 2210       Blocks: 8          IO Block: 4096  regular file
Device: 802h/2050d    Inode: 1288496     Links: 1
Access: 2024-11-18 10:50:56.000000000 +0000
Modify: 2024-11-18 10:50:56.000000000 +0000
Change: 2024-11-18 10:50:56.000000000 +0000
 Birth: -

How to Change Permissions in Linux

The command you use to change the security permissions on files is called “chmod“, which stands for “change mode” because the nine security characters are collectively called the security “mode” of the file. You can modify permissions using symbolic notation or octal notation.

1. Symbolic Notation

Symbolic notation allows you to add, remove, or set permissions for specific users. Let’s understand this using different example below:

Example 1: To Change File Permission in Linux

If you want to give “execute” permission to the world (“other”) for file “xyz.txt”, you will start by typing.

chmod o

Now you would type a ‘+’ to say that you are “adding” permission.

chmod o+

Then you would type an ‘x’ to say that you are adding “execute” permission.

chmod o+x

Finally, specify which file you are changing.

chmod o+x xyz.txt

You can see the change in the picture below.

You can also change multiple permissions at once. For example, if you want to take all permissions away from everyone, you would type.

chmod ugo-rwx xyz.txt

The code above revokes all the read(r), write(w), and execute(x) permission from all user(u), group(g), and others(o) for the file xyz.txt which results in this.

chmod ugo

Example 2:

The code adds read(r) and write(w) permission to both user(u) and group(g) and revoke execute(x) permission from others(o) for the file abc.mp4.

chmod ug+rw,o-x abc.mp4

Something like this:

chmod ug=rx,o+r abc.c

Assigns read(r) and execute(x) permission to both user(u) and group(g) and add read permission to others for the file abc.c.

There can be numerous combinations of file permissions you can invoke revoke and assign. You can try some on your Linux system.

2. Octal Notations Permissions in Linux

The octal notation is used to represent file permission in Linux by using three user group by denoting 3 digits i.e.

user
group
other users

Here’s how to permissions are mapped:

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

Permissions for owner, group, and others are represented by a three-digit octal value. The sum of permissions for each group gives the corresponding number.

Reference:

chmod o

Now you would type a ‘+’ to say that you are “adding” permission.

chmod o+

Then you would type an ‘x’ to say that you are adding “execute” permission.

chmod o+x

Finally, specify which file you are changing.

chmod o+x xyz.txt

You can see the change in the picture below.

Octal Notations Permissions in Linux

You can also change multiple permissions at once. For example, if you want to take all permissions away from everyone, you would type.

chmod ugo-rwx xyz.txt

The code above revokes all the read(r), write(w), and execute(x) permission from all user(u), group(g), and others(o) for the file xyz.txt which results in this.

Octal Notations Permissions

Example:

The code adds read(r) and write(w) permission to both user(u) and group(g) and revoke execute(x) permission from others(o) for the file abc.mp4.

chmod ug+rw,o-x abc.mp4

Something like this:

chmod ug=rx,o+r abc.c

assigns read(r) and execute(x) permission to both user(u) and group(g) and add read permission to others for the file abc.c.

There can be numerous combinations of file permissions you can invoke revoke and assign. You can try some on your Linux system.

You can also use octal notations like this.

octal notations

Using the octal notations table instead of ‘r’, ‘w’, and ‘x’. Each digit octal notation can be used for either of the group ‘u’, ‘g’, or’o’.

So, the following work is the same.

chmod ugo+rwx [file_name]
chmod 777 [file_name]

Both of them provide full read write and execute permission (code=7) to all the group.

The same is the case with this.

chmod u=r,g=wx,o=rx [file_name]
chmod 435 [file_name]

Both the codes give read (code=4) user permission, write and execute (code=3) for the group and read and execute (code=5) for others.

And even this…

chmod 775 [file_name]
chmod ug+rwx,o=rx [file_name]

Both the commands give all permissions (code=7) to the user and group, read and execute (code=5) for others.

Security Permissions in Linux

The combination for the permissions are r,w,x, and -. Let’s understand this briefly in elaborative way:

For example: “rw- r-x r–“

“rw-“: the first three characters `rw-`. This means that the owner of the file can “read” it (look at its contents) and “write” it (modify its contents). We cannot execute it because it is not a program but a text file.
“r-x”: the second set of three characters “r-x”. This means that the members of the group can only read and execute the files.
“r–“: The final three characters “r–” show the permissions allowed to other users who have a UserID on this Linux system. This means anyone in our Linux world can read but cannot modify or execute the files’ contents.

Special Permissions in Linux

Besides usual methods, Linux also offers special permission types to have more complex control over files.

1. The ‘setuid’ Command

The SET User ID permission allows user to execute programs with the previledges of its owner. Below is the example for the same:

chmod u+s program

2. The ‘setgid’ Command

The Set Group ID permission allows files to run under fule’s group permissions (or ensures the files created in a directory inherits the group of the directory). Here’s the command for the same:

chmod g+s directoryname

3. The ‘sticky bit’ Command

This allows the user (only owner) to delete or rename files within the directory (regardless of other user’s permissions). Here’s a command for the same:

chmod +t directoryname

How to Set File Permissions for a Specific User

To set permissions for a specific user or group:

1. By using chown

Use chown to change file ownsership:

chown user:group file.txt

2. By using chmod

Use chmod to modify permissions:

chmod 755 file.txt

Conclusion

Understanding file permissions in Linux is crucial for maintaining the security and integrity of your system. By using chmod, chown, and chgrp commands, you can effectively control who has access to files and directories. Regularly reviewing and managing file permissions is an essential part of system administration and security.