Adding SUID symbolically | LinuC Level 1 101 Exam original practice question

1.02.1Basic

Add set-user-ID to tool while preserving its existing ordinary permissions.

Which command is appropriate?

Hint 1: Focus on the requirement

Match the symbolic subject selector with the special bit rather than an ordinary execute permission.

Hint 2: Key terms

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

u+s: Symbolic chmod notation that adds the set-user-ID bit.
g+s: Symbolic chmod notation that adds the set-group-ID bit.
+t: Symbolic chmod notation that adds the sticky bit.
Special mode: A permission bit outside the ordinary owner, group, and other rwx bits.

Detailed explanation

Incorrectchmod g+s tool

Incorrect. g+s sets set-group-ID.

Incorrectchmod o+t tool

Incorrect. o+t sets the sticky bit.

Incorrectchmod u+x tool

Incorrect. u+x adds execute permission, not SUID.

Correctchmod u+s tool

Correct. chmod u+s tool adds the set-user-ID bit.

An example you can run in a temporary verification environment.

tmp=$(mktemp); chmod 755 "$tmp"; chmod u+s "$tmp"; stat -c '%A %a' "$tmp"; rm -f "$tmp"

-rwsr-xr-x 4755

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

Foundation review

The subject letter identifies the special bit family; u+s and g+s have different security effects.

Verify the resulting s or S display and ensure the file is an intended executable before enabling SUID.

Question IDKL-101-386

EnvironmentGNU coreutils 9.x / 空の一時ファイルを表示のみ

Last technical review2026-08-13

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