Why Two Methods?

chmod accepts both symbolic mode (letters, easy to read) and numeric (octal) mode (compact, scriptable). This lesson covers symbolic; the next covers numeric.

Symbolic Mode Syntax

chmod [who][op][perm] file

Where:

• who — u user/owner, g group, o others, a all (default if omitted).
• op — + add, - remove, = set exactly.
• perm — r read, w write, x execute, X execute only if any execute is already set or it's a directory, s setuid/setgid (with u/g), t sticky.

Common Recipes

You can combine multiple specs separated by commas: chmod u+rwx,g-w,o=r.

Recursive Mode

chmod -R u+w project/ applies to every file inside project/. Beware: blindly adding x to all files turns data files into "executables". Use the capital X:

chmod -R a+rX docs/ — adds read everywhere, but execute only on directories and files that already had any execute bit. Safe for mixed trees.

Changing Owner & Group

• chown alice file — change owner.
• chown alice:dev file — owner and group.
• chgrp dev file — group only.
• Recursive: chown -R alice:dev project/.

Worked Example

You wrote backup.sh and need:

• Owner: read, write, execute.
• Group: read, execute.
• Others: nothing.

Steps:

1. ls -l backup.sh — shows current mode, e.g. -rw-r--r--.
2. chmod u+x,g+x,o-r backup.sh — adds owner/group execute and removes others' read.
3. ls -l backup.sh — now -rwxr-x---.

Equivalent one-liner using =: chmod u=rwx,g=rx,o= backup.sh.

Symbolic vs Numeric — When to Use Which?

• Symbolic is great for incremental tweaks (chmod a+x).
• Numeric is great when you want an absolute mode regardless of the current state (chmod 755).

Common Pitfalls

• Forgetting the x bit on directories — users complain they can't cd.
• Setting world-writable on a sensitive file (chmod 777) — security disaster.
• Recursively forcing x on all files instead of using X.

Summary

• Symbolic syntax is human-readable and incremental.
• Combine who, op, and perm to make precise changes.
• Use -R plus capital X for safe recursive permission updates.