This tool helps users quickly convert between numeric and symbolic file permissions, enhancing their understanding of Linux file permissions. A Linux File Permissions Calculator helps users understand and calculate Linux file permissions, we build a tool that takes an input (either numeric mode like 755 or symbolic mode like rwxr-xr-x), and then shows the equivalent in both formats.

Symbolic Representation of Permissions

The symbolic permission string consists of 9 characters, grouped into 3 parts:

• The first 3 characters represent User (Owner) permissions.
• The next 3 characters represent Group permissions.
• The last 3 characters represent Others permissions.

Each part follows the pattern rwx (read, write, execute), where:

• r stands for Read permission.
• w stands for Write permission.
• x stands for Execute permission.
• A - means that permission is not granted.

Additionally, special permissions like s (setuid/setgid) or t (sticky bit) can appear in the last position of each part.

Breakdown of rwsr-xr-x

1. User (Owner): rws
   • r = Read: The user has permission to read the file.
   • w = Write: The user has permission to write (modify) the file.
   • s = Setuid (special permission): This means the setuid bit is set. When set on an executable file, it allows the file to be executed with the permissions of the file’s owner (not the user executing it). This is typically used for programs that need higher privileges to perform specific tasks (e.g., passwd command).
2. Group: r-x
   • r = Read: The group has permission to read the file.
   • - = No Write: The group does not have write permission.
   • x = Execute: The group has permission to execute the file.
3. Others: r-x
   • r = Read: Others have permission to read the file.
   • - = No Write: Others do not have write permission.
   • x = Execute: Others have permission to execute the file.

Summary:

• User (Owner): Has read, write, and execute permissions, and the setuid bit is set (s).
• Group: Has read and execute permissions, but no write permission.
• Others: Has read and execute permissions, but no write permission.

Numeric Representation:

• rws is treated as 7 for User (read = 4, write = 2, execute = 1, setuid = special bit).
• r-x is treated as 5 for Group (read = 4, execute = 1).
• r-x is treated as 5 for Others (read = 4, execute = 1).

So, the numeric representation of rwsr-xr-x would be 4755.