When setting file permissions through system calls like `chmod`, always use explicit octal notation (with the `0o` prefix) rather than decimal integers. Decimal integers in permission contexts can lead to unintended access rights, creating security vulnerabilities through incorrect file permissions. For example, instead of: ```python os.chmod("foo", 644) # Incorrect - decimal integer ``` Use: ```python os.chmod("foo", 0o644) # Correct - explicit octal notation ``` The decimal value `644` is not equivalent to the octal value `0o644`, and this mismatch can lead to improper permission settings that may expose sensitive files to unauthorized access. Always verify permission values in security-sensitive operations.