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LPIC-1 GNU and Unix Commands Practice Question

Exhibit

-rwxr-xr-x 1 root root 12345 Jan 1 12:00 /usr/bin/myapp
-rwsr-xr-x 1 root root 23456 Jan 1 12:00 /usr/bin/su
-rw-rw-rw- 1 user1 user1 0 Jan 1 12:00 /tmp/shared

Refer to the exhibit. Which file has a special permission that allows a user to execute the file with the privileges of the file owner?

⚠ Common exam trap

A common mix-up: candidates confuse the SUID permission with the SGID or sticky bit, or assume that any executable file in /usr/bin has special permissions, when in fact only specific system binaries like su, sudo, and passwd are configured with SUID for security reasons.

Answer choices

Why each option matters

Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.

Correct answer & explanation

✓

/usr/bin/su

The /usr/bin/su command has the SUID (Set User ID) special permission set (typically mode 4755). This allows any user who executes the file to run it with the effective user ID of the file owner (root), enabling privilege escalation to perform administrative tasks. The SUID bit is represented by an 's' in the owner's execute position when viewed with ls -l.

Answer analysis

Option-by-option breakdown

For each option: why learners choose it and why it is or isn't the right answer here.

✗
/usr/bin/myapp
Why it's wrong here
No setuid bit; permissions are rwxr-xr-x.
✗
/tmp/shared
Why it's wrong here
No setuid bit; permissions are rw-rw-rw-.
✓
/usr/bin/su
Why this is correct
Has setuid bit (rws).
✗
None of the above
Why it's wrong here
/usr/bin/su has setuid.

Go deeper

LPIC-1 GNU and Unix Commands Practice Question

Exhibit

Why each option matters

Option-by-option breakdown

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