Managing File Permissions with chmod and chown on macOS Tahoe

In macOS Tahoe, like other Unix-based systems, every file and directory has a set of permissions that determine who can read, write, or execute it. Managing these permissions via the Terminal is a critical skill for system administration and scripting.

Viewing Permissions

To see the permissions of files in your current directory, use the long-list format of the ls command:

ls -l

You will see output similar to this:

-rw-r--r--  1 user  staff  1024 Jan 1 12:00 document.txt
drwxr-xr-x  3 user  staff    96 Jan 1 12:05 MyFolder

Decoding the String

The first column (e.g., -rw-r--r--) represents the permissions.

Type: The first character indicates the file type.
- -: Regular file.
- d: Directory.
User (Owner): The next three characters (rw-).
Group: The middle three characters (r--).
Others: The last three characters (r--).

The letters stand for:

r: Read
w: Write
x: Execute (run a script or enter a directory)

Changing Permissions: chmod

The chmod (Change Mode) command modifies these access rights.

Symbolic Mode

This method uses letters to represent the changes.

u: User
g: Group
o: Others
a: All (everyone)

Examples:

Make a script executable for the user:
```
chmod u+x myscript.sh
```
Remove write permission for others:
```
chmod o-w shared_file.txt
```
Give everyone read access:
```
chmod a+r public_doc.md
```

Numeric Mode

This method uses numbers to represent the permissions (4=Read, 2=Write, 1=Execute).

7 (4+2+1): Read, Write, Execute.
6 (4+2): Read, Write.
5 (4+1): Read, Execute.
4: Read only.

Common Examples:

755 (User: rwx, Group: r-x, Others: r-x): Standard for scripts and programs.
```
chmod 755 myscript.sh
```
644 (User: rw-, Group: r--, Others: r--): Standard for text files.
```
chmod 644 document.txt
```
600 (User: rw-, Group: ---, Others: ---): Private file (like SSH keys).
```
chmod 600 private_key.pem
```

Changing Ownership: chown

The chown (Change Owner) command changes the user or group that owns a file. You usually need sudo to change ownership.

Syntax:

sudo chown [user]:[group] [file]