Understanding rw-rw-r– File Permissions in Linux

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In Linux, file and directory permissions play a crucial role in system security and user access control. The ls -l command displays these permissions in a specific format. This guide will explain what the rw-rw-r-- permission string means, ensuring clear and practical understanding.

Breaking Down rw-rw-r--

The rw-rw-r-- string represents the permissions for a file or directory and is divided into three parts, each part specifying permissions for different categories of users:

  1. Owner (User): The first rw-
  2. Group: The second rw-
  3. Others: The third r--

Detailed Breakdown

Let’s break down each part of the rw-rw-r-- permission string:

  1. Owner (User) Permissions – rw-:
  • r (Read): The owner can read the file.
  • w (Write): The owner can write to (modify) the file.
  • – (No Execute): The owner cannot execute the file.
  1. Group Permissions – rw-:
  • r (Read): Group members can read the file.
  • w (Write): Group members can write to (modify) the file.
  • – (No Execute): Group members cannot execute the file.
  1. Others Permissions – r--:
  • r (Read): Others (everyone else) can read the file.
  • – (No Write): Others cannot write to (modify) the file.
  • – (No Execute): Others cannot execute the file.

Interpreting rw-rw-r--

The rw-rw-r-- permission string means that:

  • The owner of the file has read and write permissions but cannot execute the file.
  • The group associated with the file has read and write permissions but cannot execute the file.
  • Others (all other users) have read-only permission and cannot write to or execute the file.

Setting rw-rw-r-- Permissions Using chmod

To set rw-rw-r-- permissions for a file or directory, you use the chmod command followed by the numeric representation or symbolic notation of these permissions.

Numeric Representation

The rw-rw-r-- permissions can be represented numerically as 0664:

  • Owner (rw-): 4 (read) + 2 (write) = 6
  • Group (rw-): 4 (read) + 2 (write) = 6
  • Others (r–): 4 (read) = 4

Command:

chmod 664 /path/to/file

Explanation:

  • chmod: The command to change file and directory permissions.
  • 664: Sets read and write permissions for the owner and group, and read-only permissions for others.
  • /path/to/file: The path to the file or directory you want to modify.

Symbolic Notation

Alternatively, you can use symbolic notation to set these permissions.

Command:

chmod u=rw,g=rw,o=r /path/to/file

Explanation:

  • chmod: The command to change file and directory permissions.
  • u=rw: Sets read and write permissions for the owner.
  • g=rw: Sets read and write permissions for the group.
  • o=r: Sets read-only permission for others.
  • /path/to/file: The path to the file or directory you want to modify.

Verifying Permissions

After applying the chmod command, you can verify the permissions using the ls -l command.

Example:

ls -l /path/to/file

Output:

-rw-rw-r-- 1 user group 1234 Jan  1 12:00 filename

Explanation:

  • -rw-rw-r--: Indicates read and write permissions for the owner and group, and read-only permissions for others.
  • 1 user group: Shows the file’s owner and group.
  • 1234: Indicates the file size in bytes.
  • Jan 1 12:00: Displays the date and time the file was last modified.
  • filename: The name of the file.

Common Use Cases

  • Collaborative Files: Use rw-rw-r-- for files that need to be read and modified by the owner and a specific group, but only read by others.
  • Shared Directories: Use rw-rw-r-- for directories where the owner and group members need to manage files, but others should only have read access.

Conclusion

Understanding rw-rw-r-- permissions helps manage file and directory access in Linux, ensuring security and proper control. By setting these permissions, you allow the owner and group members to read and write, while restricting others to read-only access. This approach is useful for collaborative environments where certain users need more control over files than others. Using chmod to apply these settings is straightforward, and verifying them with ls -l ensures that the correct permissions are in place.