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How to Use This Chmod Calculator

1. Set Permissions: Click checkboxes in the permission matrix to toggle read (r), write (w), and execute (x) for owner, group, and other
2. Or Enter Octal: Type an octal value (e.g., 0755) directly in the input field for instant conversion
3. Special Bits: Enable setuid, setgid, or sticky bit using the special bits row
4. View Results: See the symbolic notation, ls -l output, and ready-to-use chmod commands
5. Use Presets: Click a common preset (755, 644, 600, etc.) to apply standard permission sets
6. Copy: Use the copy buttons to copy octal, symbolic, or the full chmod command
7. Umask Tab: Switch to the Umask Calculator to determine default permissions for new files/directories

Understanding Unix Permissions

• Owner (u): The user who owns the file
• Group (g): The group that owns the file
• Other (o): All other users on the system
• Read (r = 4): View file contents or list directory contents
• Write (w = 2): Modify file contents or create/delete files in a directory
• Execute (x = 1): Run the file as a program or access a directory (cd)

Special Bits Explained

• Setuid (4xxx): When set on an executable, the program runs with the file owner's privileges (e.g., passwd). Shown as s (with x) or S (without x) in owner's execute position
• Setgid (2xxx): On executables, runs with the file group's privileges. On directories, new files inherit the directory's group. Shown as s/S in group's execute position
• Sticky Bit (1xxx): On directories, only the file owner can delete or rename their files (e.g., /tmp). Shown as t (with x) or T (without x) in other's execute position

Octal Notation Quick Reference

• 7 = rwx (4+2+1) — read, write, execute
• 6 = rw- (4+2) — read, write
• 5 = r-x (4+1) — read, execute
• 4 = r-- (4) — read only
• 3 = -wx (2+1) — write, execute
• 2 = -w- (2) — write only
• 1 = --x (1) — execute only
• 0 = --- (0) — no permissions