chmod

The chmod (change mode) command changes the access permissions of file system objects (files and directories). Permissions can be specified using symbolic mode (letters) or numeric/octal mode (numbers).

Basic Syntax

chmod [OPTION]... MODE[,MODE]... FILE...
chmod [OPTION]... OCTAL-MODE FILE...

Common Options

Option	Description
-R, --recursive	Change files and directories recursively.
-v, --verbose	Output a diagnostic for every file processed.
-c, --changes	Like verbose but report only when a change is made.

Permission Modes

Symbolic Mode:

• Classes: u (user/owner), g (group), o (others), a (all)
• Operators: + (add), - (remove), = (set exact)
• Permissions: r (read), w (write), x (execute)

Numeric Mode:

• 4 (read)
• 2 (write)
• 1 (execute)
• 0 (no permission) (Add these values for combinations: 7 = rwx, 6 = rw-, 5 = r-x)

Real-world Examples

1. Make a script executable for the owner:

   chmod u+x script.sh

2. Give read and write permissions to everyone:

   chmod a+rw file.txt

3. Set permissions to rwxr-xr-x using numeric mode:

   chmod 755 script.sh

4. Change permissions of a directory recursively:

   chmod -R 644 /var/www/html/