Choosing an octal mode with SUID | LinuC Level 1 101 Exam original practice question

1.02.1Basic

Set tool to ordinary mode 755 and add set-user-ID.

Which four-digit mode is appropriate?

Hint 1: Focus on the requirement

Interpret the leading octal digit as the special-mode field and the remaining digits as ordinary permissions.

Hint 2: Key terms

Review the short definitions before comparing the ownership and permission choices.

Detailed explanation

Correct4755

Correct. 4 for SUID followed by 755 gives 4755.

Incorrect2755

Incorrect. 2 selects SGID.

Incorrect1755

Incorrect. 1 selects the sticky bit.

Incorrect0755

Incorrect. 0 sets no special bit.

An example you can run in a temporary verification environment.

tmp=$(mktemp); chmod 4755 "$tmp"; stat -c '%a' "$tmp"; rm -f "$tmp"

Environment: GNU coreutils 9.x / 空の一時ファイル
Use a disposable file or directory when checking chmod calculations.
Exact permission display can vary slightly with filesystem and distribution defaults.

Foundation review

4755 combines SUID with ordinary mode 755; the special field is separate from the three permission triplets.

Read all four digits from left to right and confirm special-bit letters with ls or stat.

Question IDKL-101-387

EnvironmentGNU coreutils 9.x / 空の一時ファイル

Last technical review2026-08-13

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