How to Use chmod 755 in Linux [3 Best Ways]

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Last updated: July 24, 2024

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TL;DR

To use chmod 755 in Linux, you can try these methods:

  1. Use Numeric Representation: Set permissions to 755 using chmod 755 file_name to allow read, write, and execute access for the owner and read and execute access for the group and others. 
  2. Use Symbolic Representation: Set permissions using chmod u=rwx,g=rx,o=rx file_name to grant read, write, and execute access to the owner, read and execute access to the group, and read and execute access to others.
  3. Combine Numeric and Symbolic Representation: Fine-tune permissions by executing chmod 7+rwx,5+rx,5+rx file_name to set permissions to 755 while adjusting specific access levels for the owner, group, and others.

Read the article below to learn more about using chmod 755 in Linux, important security considerations, and some common mistakes to avoid.

Ever wondered how to control who can access, modify, or run your files in Linux? Well, I’ve got you covered! In this post, I’ll walk you through chmod 755, a handy command that lets you manage file permissions easily.

You’ll learn simple ways to set permissions using numbers and letters, ensuring your files stay safe and accessible. Plus, I’ll share important tips to keep your Linux system secure. Whether you’re new to this or looking to sharpen your skills, this guide will help you navigate file permissions like a pro.

What is chmod?

chmod is a command in Linux used to change the permissions of files and directories. Permissions control who can read, write, or execute a file. By using chmod, you can set these permissions to ensure proper access and security.

The basic syntax of the chmod command is:

chmod [permissions] [file or directory]

For example, to change the permissions of a file named example.txt to 755, you would use:

chmod 755 example.txt

Different Ways to Change Permissions Using chmod

You can change permissions in two ways with chmod: symbolic and numeric.

  1. Symbolic Method: Uses letters to represent permissions.
    • r for read
    • w for write
    • x for execute

Example:

chmod u+rwx,g+rx,o+rx example.txt

This gives the owner (u) read, write, and execute permissions, the group (g) read and execute permissions, and others (o) read and execute permissions.

  1. Numeric Method: Uses numbers to represent permissions.
    • 4 for read
    • 2 for write
    • 1 for execute

Example:

chmod 755 example.txt

This sets the permissions to read, write, and execute for the owner, and read and execute for the group and others.

Breaking Down chmod 755

When you set permissions to 755, you are defining what the owner, group, and others can do with a file or directory.

  1. Owner Permissions: The owner of the file or directory can read, write, and execute it.
    • The first 7 in 755 means the owner has all permissions (read, write, and execute).
    • 7 is the sum of 4 (read) + 2 (write) + 1 (execute).
  2. Group Permissions: The group members can read and execute the file or directory but cannot write to it.
    • The second 5 in 755 means the group has read and execute permissions.
    • 5 is the sum of 4 (read) + 1 (execute).
  3. Others Permissions: All other users can read and execute the file or directory but cannot write to it.
    • The last 5 in 755 means others have read and execute permissions.
    • 5 is the sum of 4 (read) + 1 (execute).

By setting a file or directory to 755, you ensure that the owner can fully interact with it, while group members and others can only read and execute it. This is useful for sharing files securely while keeping control over modifications.

How to Use chmod 755 in Linux

To use chmod 755 in Linux, you have three methods to set permissions. First, using numeric representation involves assigning a three-digit number where each digit defines permissions for owner, group, and others (e.g., chmod 755 file_name).

Second, symbolic representation uses letters (u, g, o) to specify permissions (r, w, x) for each category (chmod u=rwx,g=rx,o=rx file_name). Third, combining both methods lets you tailor permissions precisely, ensuring secure file access and execution while limiting write capabilities as needed.

Now, let’s understand the three different methods to set file permissions using chmod 755 in Linux here:

1. Use Numeric Representation

Numeric representation allows you to set permissions using a three-digit number. Each digit corresponds to a specific user category: owner, group, and others. Here’s how you can use chmod 755 in Linux using numeric representation:

  1. Identify the file or directory for which you want to set permissions. Or you can create a sample file to test-run the chmod 755 command.
create a sample file to test run the chmod 755 command
  1. Here’s the breakdown of the numeric representation to understand:
    • The 7 indicates read, write, and execute permissions for the owner.
    • The 5 signifies read and execute permissions for the group.
    • The final 5 represents read and execute permissions for others.
  2. Now, determine the appropriate numeric representation for your use case, considering the desired permissions for each user category – which, in this case, is:
chmod 755 file_name
  1. Execute the chmod 755 command in the Terminal window while replacing file_name with the actual file or directory name:
execute the chmod 755 command in the terminal window
  1. Verify the changes by listing the file permissions using the ls -l command.
file permissions using the ls l command

2. Use Symbolic Representation

Symbolic representation provides a more intuitive way of setting permissions using letters that represent users and their corresponding permissions. Let’s go through the steps:

  1. First, look for the file or directory you want to set permissions for.
look for the file or directory you want to set permissions for
  1. Explanation of symbolic notation:
    • The u stands for the owner of the file.
    • The g represents the group the file belongs to.
    • The o denotes others or everyone else.
  2. Decide which permissions you want to grant or deny for each category (e.g., read, write, or execute). In this case, you can use:
chmod u=rwx,g=rx,o=rx file_name
  1. Execute the chmod 755 command in the Linux command prompt, replacing file_name with the actual file or directory name.
execute the chmod 755 command in the linux
  1. Verify the changes by listing the file permissions using the ls -l command.
verify the changes by listing the file permissions

3. Combine Numeric and Symbolic Representation

In some cases, it may be beneficial to combine both numeric and symbolic representations. This allows you to fine-tune permissions based on specific requirements. Here’s how you can do it:

  1. Identify the file or directory for which you want to set permissions. You can use cd to navigate to the desired directory and then execute ls to view files for using the chmod 755 command. 
use cd to navigate to the desired directory
  1. With with the ls -l command, determine the permissions you wish to grant for each user category to use both numeric and symbolic representations.
permissions you wish to grant for each user category
  1. Then, execute the following command in your Terminal, replacing file_name with the actual file or directory name and adjusting the permissions accordingly:
chmod 755 file_name && chmod +rw file_name
  1. Once the commands are executed, verify the changes by listing the file permissions using the ls -l command in that particular directory.
file permissions using the ls l command in that particular directory

8 Security Considerations When Using chmod 755 in Linux

While chmod 755 provides a balance between functionality and security, it’s important to consider the following security considerations when utilizing it in a Linux environment:

  • 🔍 Regularly assess and review permissions: Perform regular assessments of file and directory permissions using the ls -l command to ensure alignment with the principle of least privilege.
  • Avoid granting unnecessary write permissions: Be cautious when granting write permissions with chmod 755. Limit write access to authorized individuals or groups using the chmod go-w file_name command.
  • 👥 Implement user and group restrictions: Leverage user and group ownership using the chown command to restrict access to sensitive files or directories. For example, chown owner:group file_name.
  • ⚠️ Consider the implications of execute permissions: Evaluate the necessity of executable permissions with chmod 755 and restrict accordingly using chmod -x file_name if not required.
  • 📝 Monitor and log permission changes: Implement logging mechanisms to track chmod 755 changes and regularly review logs using tail -f log_file to ensure consistency and detect unauthorized modifications.
  • 🔒 Implement secure file and directory ownership: Assign appropriate ownership using chown to prevent unauthorized access and modifications. For example, chown owner:group file_name.
  • 🔄 Regularly update and patch your system: Keep your Linux system up to date with the latest security patches and updates using package management tools like apt-get or yum.
  • 🔐 Enforce strong user authentication: Implement strong user authentication mechanisms, such as password policies, multi-factor authentication, or key-based authentication, using tools like passwd or ssh-keygen.

Comparison of Common chmod Permissions

Here’s a quick comparison of different chmod permission settings, their use cases, and the performance and security implications of each.

Permission Set OwnerGroupOthersPerformance and Security Implications
chmod 755Read, Write, ExecuteRead, ExecuteRead, ExecuteSecure for files that need to be executed by everyone but only modified by the owner.
chmod 777Read, Write, ExecuteRead, Write, ExecuteRead, Write, ExecuteHigh risk, as anyone can modify and execute. Use with caution, especially in shared environments.
chmod 644Read, WriteReadReadSecure for files that should not be executed, ensuring only the owner can modify.
chmod 700Read, Write, ExecuteNo AccessNo AccessVery secure, as only the owner has access. Suitable for personal or confidential files.
chmod 600Read, WriteNo AccessNo AccessVery secure, ensuring only the owner can read and modify.

To Sum Up

To wrap up, using the chmod 755 command in Linux is straightforward. You can use numeric representation (chmod 755 filename) or symbolic representation (chmod u=rwx,g=rx,o=rx filename). Both methods ensure you have full control while others can only read and execute.

To expand your knowledge further, I recommend checking out my articles on:

Frequently Asked Questions

What is the difference between chmod 755 and chmod 777?

The main difference between chmod 755 and chmod 777 lies in the level of permissions they grant. When you use chmod 755, it sets the owner’s permissions to read, write, and execute (rwx), while allowing the group and others to have read and execute permissions (rx), but no write access. On the other hand, chmod 777 grants full read, write, and execute permissions to all users, including the owner, group, and others. However, it’s important to note that using chmod 777 can potentially compromise security, as it provides unrestricted access to the file or directory.

Can I use chmod 755 on directories as well?

Certainly, you can use chmod 755 to set permissions on directories. However, be cautious as it grants execute permissions, enabling users to access and list the directory contents. Consider the sensitivity of the information within the directory and assess whether it is necessary for users other than the owner to have the execute access. Adjust the permissions accordingly based on the security requirements of your system.

How can I recursively apply chmod 755 to all files and folders within a directory?

To recursively apply chmod 755 to all files and folders within a directory, you can use the -R (or --recursive) option with the chmod command. For example, use the following command: chmod -R 755 directory_name. This command applies chmod 755 to the specified directory (directory_name) and all its files and subdirectories. Exercise caution when using the -R option, as it will affect the permissions of all nested files and directories.

Is it possible to revert the permissions set by chmod 755?

Yes, you can revert the permissions set by chmod 755. Use the command chmod go-rwx file_name to remove the read, write, and execute permissions for the group (g) and others (o), while retaining the owner’s permissions. This effectively eliminates write and execute permissions for the group and others, leaving only the owner with read, write, and execute permissions. Make sure to specify the correct file name and verify the resulting permissions to ensure they align with your desired configuration.

Ojash

Author

Ojash is a skilled Linux expert and tech writer with over a decade of experience. He has extensive knowledge of Linux's file system, command-line interface, and software installations. Ojash is also an expert in shell scripting and automation, with experience in Bash, Python, and Perl. He has published numerous articles on Linux in various online publications, making him a valuable resource for both seasoned Linux users and beginners. Ojash is also an active member of the Linux community and participates in Linux forums.

Akshat

Reviewer

Akshat is a software engineer, product designer and the co-founder of Scrutify. He's an experienced Linux professional and the senior editor of this blog. He is also an open-source contributor to many projects on Github and has written several technical guides on Linux. Apart from that, he’s also actively sharing his ideas and tutorials on Medium and Attirer. As the editor of this blog, Akshat brings his wealth of knowledge and experience to provide readers with valuable insights and advice on a wide range of Linux-related topics.

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