chmod Octal vs Symbolic: Knowing When to Use Each

File permissions are set incorrectly or inconsistently because developers mix octal and symbolic chmod notation without understanding the difference in semantics.

Use octal for setting absolute permissions, use symbolic for relative (additive/subtractive) changes.

# Octal: set exact permissions (rwxr-xr-x)
chmod 755 /usr/local/bin/myscript

# Symbolic: add execute for owner only
chmod u+x script.sh

# Symbolic: remove write from group and other
chmod go-w sensitive.conf

# Recursive: only change directories (not files)
find /var/www -type d -exec chmod 755 {} +

# Recursive: only change files
find /var/www -type f -exec chmod 644 {} +

Octal replaces all permission bits in one shot. Symbolic modifies specific bits without touching others. Using octal recursively on a tree that mixes files and directories is a common mistake that makes all files executable.