Setting a sensitive file to mode 640 | LinuC Level 1 101 Exam original practice question

1.02.1Basic

Set secret.txt to owner read/write, group read, and no permissions for others.

Which command is appropriate?

Hint 1: Focus on the requirement

Convert read, write, and execute to 4, 2, and 1 for owner, group, and other in that order.

Hint 2: Key terms

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

Octal mode: A numeric representation of permission bits in owner, group, and other order.
Read bit: The permission value represented by 4 in one octal triplet.
Write bit: The permission value represented by 2 in one octal triplet.
Zero mode: An octal digit that grants none of the ordinary rwx permissions.

Detailed explanation

Incorrectchmod 460 secret.txt

Incorrect. 460 assigns the digits to the wrong classes.

Incorrectchmod 604 secret.txt

Incorrect. 604 grants other users read permission and changes the intended classes.

Correctchmod 640 secret.txt

Correct. chmod 640 secret.txt sets rw-r-----.

Incorrectchmod 644 secret.txt

Incorrect. 644 grants other users read permission.

An example you can run in a temporary verification environment.

tmp=$(mktemp); chmod 640 "$tmp"; stat -c '%A %a' "$tmp"; rm -f "$tmp"

-rw-r----- 640

Environment: GNU coreutils 9.x / 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

640 means owner read/write, group read, and no ordinary permission for other users.

Keep the three octal digits aligned with owner, group, and other; do not swap group and other.

Question IDKL-101-376

EnvironmentGNU coreutils 9.x / 一時ファイル

Last technical review2026-08-13

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