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...Read more
TL;DR
To use chmod 755 in Linux, you can try these methods:
- Use Numeric Representation: Set permissions to 755 using
chmod 755 file_nameto allow read, write, and execute access for the owner and read and execute access for the group and others. - Use Symbolic Representation: Set permissions using
chmod u=rwx,g=rx,o=rx file_nameto grant read, write, and execute access to the owner, read and execute access to the group, and read and execute access to others. - Combine Numeric and Symbolic Representation: Fine-tune permissions by executing
chmod 7+rwx,5+rx,5+rx file_nameto set permissions to 755 while adjusting specific access levels for the owner, group, and others.
When using chmod 755 in Linux, consider security, avoid mistakes, and identify the best use cases. Review permissions regularly, avoid unnecessary write access, and implement user and group restrictions. Common mistakes include applying it to sensitive files and relying solely on numeric representation. Best use cases include securing executable files and enabling read access for everyone. By understanding these aspects, you can use chmod 755 effectively.
Read the article below to learn more about using chmod 755 in Linux, important security considerations, and some common mistakes to avoid.
File permissions play a crucial role in the Linux operating system, providing control over who can access, modify, or execute files. Among the various permissions available, chmod 755 is a commonly used setting that strikes a balance between security and functionality. In this article, I will explain the three best ways to use chmod 755 in Linux with step-by-step instructions, some security concerns, and common mistakes to avoid.
How to Use chmod 755 in Linux
To use chmod 755 in Linux, you can use numeric representation by executing chmod 755 file_name. Alternatively, you can utilize symbolic representation with chmod u=rwx,g=rx,o=rx file_name. But if you need more precise control, combine both methods by executing chmod 7+rwx,5+rx,5+rx file_name. After you execute any of these methods, make sure to verify the permissions using ls -l. 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:
- Identify the file or directory for which you want to set permissions. Or you can create a sample file to test-run the
chmod 755command.
- 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.
- 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- Execute the
chmod 755command in the Terminal window while replacingfile_namewith the actual file or directory name:
- Verify the changes by listing the file permissions using the
ls -lcommand.
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:
- First, look for the file or directory you want to set permissions for.
- Explanation of symbolic notation:
- The
ustands for the owner of the file. - The
grepresents the group the file belongs to. - The
odenotes others or everyone else.
- The
- 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- Execute the chmod 755 command in the Linux command prompt, replacing
file_namewith the actual file or directory name.
- Verify the changes by listing the file permissions using the
ls -lcommand.
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:
- Identify the file or directory for which you want to set permissions. You can use
cdto navigate to the desired directory and then executelsto view files for using thechmod 755command.
- With with the
ls -lcommand, determine the permissions you wish to grant for each user category to use both numeric and symbolic representations.
- Then, execute the following command in your Terminal, replacing
file_namewith the actual file or directory name and adjusting the permissions accordingly:
chmod 755 file_name && chmod +rw file_name- Once the commands are executed, verify the changes by listing the file permissions using the
ls -lcommand 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 -lcommand 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_namecommand. - 👥 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_nameif not required. - 📝 Monitor and log permission changes: Implement logging mechanisms to track chmod 755 changes and regularly review logs using
tail -f log_fileto 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-getoryum. - 🔐 Enforce strong user authentication: Implement strong user authentication mechanisms, such as password policies, multi-factor authentication, or key-based authentication, using tools like
passwdorssh-keygen.
8 Common Mistakes to Avoid When Using chmod 755 in Linux
When working with chmod 755 in Linux, it’s important to be aware of common mistakes that can lead to unintended consequences or compromise system security. By avoiding these mistakes, you can ensure the proper usage of chmod 755 and maintain a secure environment. Here are some common pitfalls to avoid:
- 🔒 Applying chmod 755 to Sensitive Files: One of the most critical mistakes is applying chmod 755 to files that contain sensitive information or require stricter permissions. Always evaluate the sensitivity of the data and ensure that appropriate permissions are set to protect confidential or critical files.
- 📂 Incorrectly Applying Permissions to Directories: When setting permissions using chmod 755, be careful when working with directories. Applying permissions to directories without considering the contents or using recursion when required can lead to unintended changes or expose sensitive information.
- ⚠️ Neglecting Implications of Read, Write, and Execute Permissions: Each permission (read, write, and execute) has distinct implications. Failing to understand these implications can result in granting excessive access rights or limiting necessary permissions, impacting the functionality and security of files and directories. Take the time to comprehend the purpose and requirements of each permission.
- 👥 Ignoring User Categories: Understanding the three user categories (owner, group, and others) is crucial. Neglecting to assign permissions appropriately for each category can lead to unauthorized access or hinder legitimate usage. Make sure to assign permissions based on user categories to ensure proper access control.
- 🔢 Relying Solely on Numeric Representation: While numeric representation (755) is commonly used, relying solely on it can make it challenging to understand the specific permissions assigned. Utilize symbolic representation (u, g, o) and combine it with numeric notation when necessary. This approach enhances readability and allows for finer-grained control over permissions.
- 📝 Failing to Document Permission Changes: Neglecting to document permission changes made with chmod 755 can lead to confusion and difficulties in managing file permissions. Maintain a record of modifications, including the rationale behind the changes. Documentation helps with troubleshooting, audits, and maintaining a clear overview of the permissions set.
- 🧪 Not Testing Permissions: After applying chmod 755 to files or directories, it is crucial to test the permissions. Verify that the intended users can access the files and execute necessary actions while ensuring that unauthorized access or modifications are appropriately restricted.
- ❓ Misunderstanding the Difference Between chmod 755 and chmod 777: Be aware of the distinction between chmod 755 and chmod 777. While both settings provide read and execute permissions, chmod 777 grants full read, write, and execute permissions to all users. Using chmod 777 in situations where chmod 755 is sufficient can introduce unnecessary security risks.
To Sum Up
In summary, this article has provided a complete guide on using chmod 755 in Linux. By understanding the numeric and symbolic representations, you can easily set permissions according to your needs. It is important to follow best practices, consider security implications, and avoid common mistakes.
To expand your knowledge further, I recommend checking out my articles on how to make files executable, count files in a directory, and view the content of files in Linux. These topics are explained in a beginner-friendly manner and cover relevant aspects. With this information, you’ll develop a solid understanding of managing file permissions in Linux and ensuring a secure system.
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.
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.
