Basic Linux Permissions: How to Check & Change Them

One of the best things about Linux systems is that they are thought to be safer than other systems when it comes to vulnerabilities and flaws. Linux definitely gives users more freedom and smoother control over the security rights of its file systems. This could mean that Linux users need to know a lot about security rights. That isn’t necessarily true, but it’s still wise for beginning users to understand the basics of Linux permissions. In this article, we will discuss Linux file permissions and how to change and check Linux permissions.

What Is Linux Permissions?

Linux permissions are a critical aspect of the operating system’s security model, governing access to files and directories. They operate on the principle of three entities: users, groups, and others.

User Permissions:

• Read (r): Enables viewing and reading of files.
• Write (w): Permits modification or deletion of files.
• Execute (x): Grants the ability to run executable files or traverse directories.

Group Permissions:

• Similar to user permissions, they are applied to a designated group of users. Group members inherit these permissions.

Other Permissions:

• Apply to anyone else who is not the user or part of the specified group.

Furthermore, permissions are expressed using a symbolic notation (e.g., rw-r–r–) or numeric representation (e.g., 644). The notation consists of three characters for each entity, indicating read, write, and execute permissions.

Commands like chmod are used to modify permissions, ensuring controlled access. Proper permission management is vital for system security, preventing unauthorized access or unintended modifications. Users can change ownership with chown and group ownership with chgrp. In addition, this granular control over file access contributes to the robustness and integrity of Linux systems.

What Do Linux File Permissions Actually Do?

Linux file permissions play a crucial role in regulating access to and control over files and directories, ensuring system security and privacy. They define who can perform specific actions, such as reading, writing, or executing, on a given file or directory. There are three primary permission categories: owner, group, and others.

• Read (r): Allows users to view the content of a file or list the contents of a directory. Without read permission, users cannot read the data within the file or see the files within a directory.
• Write (w): Grants users the ability to modify the contents of a file or create, delete, and rename files within a directory. Without written permission, users are restricted from making changes.
• Execute (x): Enables users to execute a file if it’s a program or script. For directories, execute permission is necessary to access their contents. Without execute permission, users cannot run programs or access the contents of a directory.

By combining these permissions in a three-digit code (e.g., 740), Linux administrators can fine-tune access control. This allows them to follow the principle of least privilege, granting only the necessary permissions to users and groups. Properly configured file permissions contribute significantly to system security by preventing unauthorized access, accidental modifications, and the execution of malicious code. They are an integral part of Linux’s multi-layered security model. Also, read HOW TO CREATE A FILE IN LINUX: EASY Guide

How Do Directory Permissions Work?

Directory file types are represented with d. While the basic tenets of permissions are consistent across directories, their implementations vary widely.

#1. Read (r) 

Like ordinary files, this permission allows you to view the contents of the directory. But that only means that you have read access to whatever files happen to be in that directory. For example, the LS command cannot function without this access.

#2. Write (w)

The directory’s contents can be changed in the same way that regular files can be. Changing a directory’s contents entails doing one of two things: either adding files to the directory or deleting items from the directory. Therefore, in order to rename (nm) or delete (rm) files from a directory, you need to have write permission in that directory. In order to copy (cp) or create (touch) files in a directory, you must have written permission.

#3. Execute (x)

This access control works quite differently on directories than it does on files. Essentially, you may think of it as offering access to the directory. If you have execute permission on a directory, you can not only use commands like cd and ls to navigate through its contents, but you can also see detailed information about each file in the directory by using ls -l.

When a directory lacks execute permission, it might restrict other permissions in unusual ways. For instance, even if you have to write permission for a directory, if you don’t have access to the directory’s metadata, you won’t be able to add a new file to the directory. Not possible. It is for this reason that directory-type files often grant execute access to one or more of the user owners, group owners, or others.

When Permissions Are Important

You may not give permissions much thought if you use a Mac or Windows computer, but that’s because those operating systems and their surroundings tend to put less emphasis on user-based rights on files. Permission-based security, however, has been greatly simplified and may now be used in whichever way you see fit now that you are using a Linux-based system.

Consequently, I will demonstrate the ideal permissions for a few files and directories that you should be working with.

#1. Home Directories

Because you do not want other users to be able to see or change the data in another user’s documents or desktop, the home directories of such users are crucial. The drwx______ (700) permission set is what you’ll need to fix this, so let’s pretend we want to fix the permissions on user user1’s home directory by typing chmod 700 /home/user1.

#2. Bootloader Configuration Files

If you wish to require a password in order to boot some operating systems, you’ll need to ensure that no one except the root has access to the configuration file. Setting the file’s permissions to 700 will do this.

#3. System and Daemon Configuration Files

To prevent users from making changes to crucial system and daemon configuration files, it is essential to limit their write access. It may not be necessary to limit users’ read access, although doing so is strongly recommended. Sometimes increasing the rights to 644 is the best option.

#4. Firewall Scripts

While it may not always be required to prevent people from accessing the firewall file, it is recommended that they be prevented from writing to the file. You can safely grant everyone else only 700 permissions because the root user runs the firewall script right away after booting.

Check File Permissions in Linux

Finding the existing Linux permission settings is the first step when dealing with file permissions. You can either use the command-line interface or the graphical user interface to verify the information.

Check Permissions using GUI

With a graphical user interface (GUI), locating the permission for a file or directory is a breeze.

1. The properties of a file can be viewed by finding its icon, right-clicking on it, and selecting the option.
2. When you click this, a new window will appear with some fundamental file info in it. Navigate to the second tab in the window, called Permissions.
3. In that section, you’ll notice that the file permissions vary between three types:

• Whoever creates the file or directory is considered the owner.
• membership in (the owner’s) group
• Others (everyone else)

The file’s owner can decide who has access based on their membership in predefined groups.

The owner of the file test.txt in our example has “read and write” permissions, but other members of its group and all other users only have “read-only” permissions. As a result, they can view the file but cannot make any changes to it.

To make a change to the file’s settings, the user simply opens the category-specific drop-down menu and makes the appropriate permission selection. By selecting the Execute checkbox, the file will be made executable and can be run as a program.

How Do I Give 777 Permission to Folders and Subfolders in Linux?

Assigning 777 permissions to a folder and its subfolders in Linux grants full read, write, and execute access to the owner, group, and others. However, it’s crucial to exercise caution when using these permissions, as they can pose security risks.

To set 777 permissions on a folder and its subfolders, you can use the chmod command along with the -R option for recursive applications. Here’s an example:

chmod -R 777 /path/to/your/folder

In this command:

• chmod is the command for changing permissions.
• -R ensures that the permissions are applied recursively to all files and subdirectories within the specified folder.
• 777 assigns read (4) + write (2) + execute (1) permissions to the owner, group, and others.

However, be cautious about using 777 permissions, as it allows anyone to perform any action on the files, posing security risks. It’s recommended to use the least permissive permissions necessary for your specific use case. Consider whether a more restricted set of permissions (e.g., 755 or 700) might meet your needs while maintaining a higher level of security.

Change Linux Permissions

Changing Linux permissions is a common task for controlling access to files and directories. The chmod command is used for this purpose. Here’s a brief guide on how to change permissions:

Symbolic Method:

The symbolic method uses symbols to represent permission changes.

1. View current permissions:

ls -l file_or_directory

2. Change permissions:

chmod who_operator permission file_or_directory

• who specifies whose permissions to change (u for a user, g for a group, o for others, a for all).
• operator indicates whether to add (+), remove (-), or set (=) permissions.
• permission denotes the permission to change (e.g., r for read, w for write, x for execute).

Example:

chmod u+x file   # adds execute permission for the owner.

Numeric Method:

The numeric method employs octal values to represent permission sets.

1. View current permissions:

ls -l file_or_directory

2. Change permissions:

chmod octal_value file_or_directory

• octal_value is a three-digit number representing the permission set for the user, group, and others.

Example:

chmod 644 file   # Sets read and write for the owner, and read for group and others.

Remember to use the -R option with chmod for recursive changes in directories. Always consider the security implications of permission changes, aiming for the minimum necessary permissions to ensure data integrity and system security.

What Is 740 Permission in Linux?

Each digit in the three-digit code for file permissions in Linux stands for one of the user categories—owner, group, or others. The number 740 signifies specific permissions for a file or directory.

• The first digit (7) represents the owner’s permissions. In this case, it’s 7, indicating read (4), write (2), and execute (1) permissions combined, allowing the owner to read, write, and execute the file.
• The second digit (4) signifies the group’s permissions, granting read-only access.
• The third digit (0) represents permissions for others, indicating no permissions.

So, a file with 740 permissions means that the owner has full control (read, write, execute), the group has read access only, and others have no permissions. This configuration balances security by restricting access to only those who need it, following the principle of least privilege. It is important to set permissions carefully to ensure the confidentiality and integrity of files and directories.

How Do You Read File Permissions?

Reading file permissions in Linux involves understanding a three-digit code and its corresponding permission sets for the owner, group, and others. Each digit is a sum of specific permissions.

The first digit represents the owner’s permissions: 4 for read, 2 for write, and 1 for execute. To read this digit, add the values of the permissions the owner has. For example, if the owner has read and written but not executed, the digit is 6 (4 for read + 2 for write).

The second digit signifies group permissions, using the same read (4), write (2), and execute (1) values. Calculate it similarly to the owner’s digit.

The third digit is for others’ permissions, applying the same values. Add the permissions for others.

Combining these three digits, you get a three-digit code like 740, which signifies read, write, and execute for the owner, read-only for the group, and no permissions for others. Reading file permissions is crucial for managing access and security on a Linux system.

What is 755 permission in Linux?

For executable files and directories, the permission set “755” is a typical configuration in Linux, which uses a three-digit code to represent file permissions.

• The first digit (7) signifies the owner’s permissions. In this case, it allows the owner to read (4) + write (2) + execute (1), providing full control over the file or directory.
• The second digit (5) represents the group’s permissions. It grants read (4) + execute (1) permissions, allowing group members to view the file’s content and execute it if it’s a script or program.
• The third digit (5) is for others’ permissions, providing read (4) + execute (1) access. This means anyone else, not the owner or anyone in the group, can read the file or execute it if applicable.

In summary, the 755 permission setting is commonly used for executable files and directories, ensuring that the owner has full control, the group can read and execute, and others can also read and execute. This balance allows for the secure execution of programs while restricting unnecessary write permissions.

What Is Chmod 666 vs. 777?

In Linux, the chmod command is used to change file permissions. The numbers following chmod represent the permission modes assigned to the file. Comparing chmod 666 and chmod 777 illustrates different levels of permission.

• chmod 666: This sets read (4) and write (2) permissions for the owner, group, and others. No execute permission (1) is granted. Essentially, it allows anyone to read from and write to the file but doesn’t allow execution. For files that multiple users need to edit or modify, this is a common practice.
• chmod 777: This provides full permissions—read, write, and execute—to the owner, group, and others. It grants unrestricted access to the file, allowing anyone to read from, write to, and execute the file. While this setting can be useful for specific scenarios, it poses security risks by giving everyone complete control over the file, which may not be desirable in most situations.

In practice, it’s essential to be cautious when using chmod 777, as it can expose sensitive files to unintended modifications or executions. It’s advisable to use the minimum necessary permissions to maintain security.

What is chmod 777 and 644?

The chmod command in Linux is used to change file permissions, and chmod 777 and chmod 644 represent different levels of access for files.

• chmod 777: This setting grants read (4), write (2), and execute (1) permissions to the owner, group, and others. In essence, it provides full control to everyone, allowing any user to read from, write to, and execute the file. While it offers maximum flexibility, it can pose security risks if used indiscriminately, as it grants unrestricted access.
• chmod 644: This configuration is more restrictive. It gives read (4) and write (2) permissions to the owner, allowing the file’s owner to modify its content. The group is granted read access (4), enabling group members to view the file’s content without modification. Others, users not in the owner group, are given read-only access. This is a common setting for non-executable files, striking a balance between accessibility and security, ensuring that only the owner can modify the file.

In summary, chmod 777 is more permissive, while chmod 644 provides a balance between accessibility and security. The appropriate choice depends on the specific requirements and security considerations of the file in question.

What is 777 Permission in Linux?

In Linux, file permissions are expressed as a three-digit code, and “777” is a permission setting that provides full access to a file or directory for the owner, group, and others.

• The first digit (7) signifies the owner’s permissions: read (4) + write (2) + execute (1). This grants the owner complete control, allowing them to read, write, and execute the file or directory.
• The second digit (7) represents the group’s permissions, offering the same read (4) + execute(1) access. Group members have the same level of control as the owner.
• The third digit (7) is for others’ permissions, providing read, write, and execute access to anyone who is not the owner or part of the group.

Setting permissions to 777 is extremely permissive, as it allows any user to perform any action on the file or directory. While this can be useful in certain situations, such as temporary testing environments, it poses significant security risks. Using 777 should be done with caution, as it can lead to unauthorized access, modifications, or execution of files, potentially compromising system integrity and confidentiality. It’s generally recommended to use more restrictive permissions whenever possible to enhance security.

Bottom Line

Checking and changing the permissions of Linux files and directories are fundamental skills for each user. Our article on using the chgrp command to alter file group permissions may prove useful in this regard.

Whether you’re more comfortable with a graphical user interface or a command line, you should be able to apply the knowledge you gain here to better manage your files’ rights.

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Reference

• redhat.com
• geeksforgeeks.org
• linuxfoundation.org
• phoenixnap.com